Winter hoophouse growing

 

Hoophouse Yukina savoy at the end of November.
Photo Ethan Hirsh

Last week I wrote about Winter Preparations for Vegetable Gardens. For those with a hoophouse, here are some notes on all the work we can do to grow winter crops there! For those without a hoophouse as yet, scroll to the end for Twenty Benefits of Having a Hoophouse

First, a roundup of previous blogposts on winter hoophouse topics.

Planning winter hoophouse crops includes a description of how we do our hoophouse crop planning so we can maintain a crop rotation and still pack the beds fully with hardy crops.

Fall hoophouse bed prep and shadecloth removal includes spreading compost, broadforking, and a step-by-step guide to hoophouse fall bed prep.

Hoophouse fall bed prep Plans A-D and spider-webs includes some lovely spider photos and a short video of ballooning, as well as info about our first-planted winter crops.

Hoophouse bed broadforked to loosen up slumped soil. I’m happy to say our soil structure has improved in the 18 years since this photo was taken!
Photo Pam Dawling

Young greens in the hoophouse

After the set-backs with our winter hoophouse greens transplants that I wrote about in Hoophouse fall bed prep Plans A-D and spider-webs, we worked really hard and got the whole house planted up. Most of the transplants have recovered from their transplant shock (wilting each day), during the cloudy weather we had.

The new seedlings are coming up fast and calling on us to thin them. We ended up not needing so many of the Plan D plug flat plants, but we’ve kept them for now “in case” .

Plan D: Winstrip seed flats in our hoophouse on Oct 16, a late attempt to catch up!
Photo Pam Dawling

Ultimately if we don’t need them, they’ll go in a salad mix. I wrote about Making baby salad mix last year. The past two days I have been able to harvest a mix in the hoophouse. The ingredient we are shortest of is lettuce. My first mix was spinach, Bulls Blood beet leaves, a few leaves of Tokyo Bekana, Bright Lights chard, Scarlet Frills, Ruby Streaks and Golden Frills, and a handful of lettuce leaves Red Tinged Winter is growing fastest, of all the varieties we planted this year.

Sowing hoophouse winter crops includes some discussion of the tools we like; pre-sprouting spinach seed and growing multi-leaf lettuce.

What’s growing in the hoophouse; reading; planning for winter is an October view of crops.

Frilly Mustards in our Winter Hoophouse is exactly what it sounds like. Four sowings, six varieties. All delicious.

Making baby salad mix includes a discussion of ingredients and methods, balancing nutrition, color, shape and loft.

Young green Panisse and red Revolution lettuce in our hoophouse in November.
Photo Pam Dawling

Cold-tolerant lettuce and the rest, our January 2018 assessment of the varieties we grew that winter and which survived the unusually cold spell we had. Includes sad photos of the casualties!

Also see my Mother Earth News blogpost from August 2018 Grow Great Lettuce in Winter

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Hoophouse seedlings growing outdoors under insect netting. Starting transplants outdoors helps the rotation by reducing the time the crop is growing in the hoophouse
Photo Pam Dawling

Do you value crop rotation in your hoophouse?

In the winter 2019-2020, a reader in the Pacific Northwest wrote: “This winter I have been re-thinking my crop rotation plan after having some issues (with flea beetle larvae in the soil outsmarting my diligent insect netting of my brassica salad crops). These days I see intensive market gardeners seeming to not worry so much about rotation (i.e. Neversink farm, etc), and yet I’ve always been taught that it is such an important principle to follow. I reviewed your slideshows on crop rotation and also cool crop planning in the greenhouse (which briefly addresses salad brassica rotation with other crops). With how much space I have and the high demand I have for brassicas, for salad mix (mustards) and also the more mainstay cole crops, I had settled on a 2.5 yr between brassica crop rotation (but planting two successions of mustards in the same bed within one year, in the year the bed was in mustards, with a lettuce or other crop breaking up the successions, with the idea that they were very short day and also light feeder crops). Wondering if you think this just doesn’t sound cautious enough, or if this sounds like a reasonable compromise with not having more space to work with (and wanting to satisfy the market demand for brassicas).”

I replied: “Yes, I do think crop rotation is important. I do know some farms seem to have given it up. I think what you are seeing shows one reason why rotation is important. In our hoophouse, we do as you do, allocating brassicas to a space for that winter season and perhaps doing more than one round of brassica crops. Then moving away from brassicas for the next two winters. If doing that doesn’t get rid of the flea beetle problem, and you are being thorough about netting with small-enough mesh netting (sounds like you are, but maybe check the mesh size), then my next step would be spinosad when the flea beetles appear. You can spray the inside of the netting too, and close it quickly. It’s that or a longer rotation, which it sounds like is not financially viable. You could also try farmscaping and/or importing predatory insects (not sure if there are any), Are there beneficial nematodes that attack flea beetle larvae? These are things I don’t know about, but might be worth looking into.”


Doing a spot of research today, I find that Heterorhabditis bacteriaphora, (Hb nematodes) a beneficial nematode fromArbico Organics will attack flea beetles. also known as NemaSeek, and sold separately. This is the wrong time of year for introducing nematodes in most of the US. They need warm weather to thrive.

Another suggestion from Arbico is BotaniGard Maxx & other B. bassiana sprays, which infect and kill adult flea beetles. Repeat applications as needed throughout the growing season.

Kaolin clay (Surround) is another possibility.

Also see Harvest to Table on the topic of dealing with flea beetles

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View through the hoophouse doors in December.
Photo Kathleen Slattery

Add a hoophouse to your food production

For those of you wistfully thinking about a hoophouse, let me help you a step closer to having one next year! Sales of my Year-Round Hoophouse book are doing well, which suggests to me that quite a few gardeners and growers are thinking in this direction.

Twenty Benefits of Having a Hoophouse

  1. An extended growing season because plants are protected from cold weather.
  2. Faster growth and higher total yields.
  3. Beautiful unblemished crops not battered by the elements.
  4. Fewer foliar diseases because the leaves can stay dry.
  5. Crop survival at lower temperatures in the hoophouse than is possible outdoors.
  6. Better crop recovery in winter due to warm sunny days following the cold nights.
  7. Some protection from deer and other pests large and small.
  8. Soil temperature stays above 50F (10C) in zone 6b. Warm soil = faster cold weather growth.
  9. Higher proportion of usable crops – more food, higher sales dollars.
  10. Diverse crop portfolio – grow crops that wouldn’t succeed outdoors in your climate.
  11. Harvest whenever you need the crops, even during pouring rain!
  12. Wonderful working conditions – no need for gloves and hats; take off your coat.
  13. A food garden on a manageable scale.
  14. A place to enjoy practicing intensive food production.
  15. The chance to have an area completely free of weeds – new weed seed doesn’t blow in.
  16. No need to work with heavy machinery.
  17. Much better value for producing crops (per dollar invested) than a heated greenhouse.
  18. Can be constructed by generally-handy people. Specialists are not needed.
  19. NRCS grants are available for some hoophouses. Natural Resources Conservation Service, Environmental Quality Incentives Program, High Tunnel System Initiative.
  20. Ecological energy use. The embodied energy of the plastic is less than the energy that would be used to ship similar produce from somewhere warmer (Eliot Coleman, Four Season Harvest). Another study found this was not true for smaller (9 x 12 m) hoophouses – although the economic incentive for growers is still true, there is no energy efficiency advantage to the planet. Smaller carbon footprint: shipping 1 kg lettuce has 4.3 times the CO2 footprint of locally grown hoophouse lettuce. Plawecki, R., Pirog, R., Montri, A., & Hamm, M. (2014). Comparative carbon footprint assessment of winter lettuce production in two climatic zones for Midwestern market. Renewable Agriculture and Food Systems, 29(4), 310-318. doi:10.1017/S1742170513000161.
September sown White Russian kale (transplanted in October).
Photo Wren Vile

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Know your climate

WeatherSpark climate summary for Louisa, Virginia. Go to the website to click for more information

The WeatherSpark website provides “The Typical Weather Anywhere on Earth”. Enter your nearest town or airport and you get clearly explained info with fascinating graphics of how the weather goes over the year in your locality. Note this is not a forecast site, it’s about average weather for each place. Useful to people who’ve recently moved and want to know what to expect this winter, or to new gardeners who haven’t paid so much attention previously. Or to those who want to check their assumptions (I really thought the wind was out of the west more of the time than records say). There are charts of high and low temperature, temperature by the hour each month, cloud cover, daily chance of precipitation (both rainfall and snowfall), hours of daylight, humidity, wind speed and direction and solar energy. A big help in making wise decisions. I know that climate change is going to cause havoc with averages, and we’ll need to learn to become better weather forecasters individually, and to use soil temperature and other metrics to decide when to plant. This website explains things well.

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Winter gives a time for most of us to ponder success, failure, and possibilities for doing things differently.

 

Winter Preparations for Vegetable Gardens

 

Frosty daikon radish
Photo by Bridget Aleshire

Winter-Kill Temperatures

My annual blogpost of Winter-Kill Temperatures for Cold-Hardy Vegetables is always very popular. In fact, it’s my most popular title! Usually searches for this info increase in October and peak in early November, so here are quick links for those of you who have been meaning to look something up.

Winter-Kill Temperatures of Cold-Hardy Vegetables 2020

Winter Kill Temperatures of Cold-Hardy Vegetables 2019

Winter-Kill Temperatures of Cold-Hardy Vegetables 2018

Winter Kill Temperatures of Winter-Hardy Vegetables 2016

Trimming roots from a leek in December.
Photo Pam Dawling

For several years, starting in 2012, my friend and neighboring grower Ken Bezilla of Southern Exposure Seed Exchange and I have been keeping records of how well our crops do in the colder season. Ken provided much of the original information, and has suggested the morbidly named Death Bed idea: set aside a small bed and plant a few of each plant in it to audition for winter hardiness. Note each increasingly cold minimum temperature and when the various crops die of cold, to fine-tune your planting for next year (and leave me a comment!) Each year I update the list, based on new things I learned during the recent winter.

We are in zone 7a, with an average annual minimum temperature of 0-5°F (-18°C to -15°C).

The winter 2019-2020 was mild, with our lowest temperature being a single night at 12°F (-11°C). The Koji greens became completely unmarketable but did not completely die. Yukina Savoy is indeed hardier (as I expected), being OK down to 10°F (-12°C). We had one night at 13°F (-10°C) and two each at 17°F (-8°C), 18°F (-8°C also) and 19°F (-7°C). That winter I noted the death of rhubarb stems and leaves at 25°F (-4°C), rather than 22°F (-6°C), as I noted a year or two ago. I also added some cover crop hardiness temperatures.

Rhubarb in spring.
Photo Kathryn Simmons

I also learned that there is more damage when the weather switches suddenly from warm to cold. And that the weatherman in Raleigh, NC says it needs 3 hours at the critical temperature to do damage. Also note that repeated cold temperatures can kill off crops that can survive a single dip to a low temperature, and that cold winds, or cold wet weather can destroy plants quicker than simple cold. All greens do a lot better with row cover to protect them against cold drying winds.

Winter hoophouse lettuce
Photo Kathryn Simmons

It’s worth noting that in a double-layer hoophouse (8F/5C warmer at night than outside) plants can survive 14F/8C colder than they can outside, without extra rowcover; at least 21F/12C colder than outside with thick rowcover

Salad greens in a hoophouse in zone 7 can survive nights with outdoor lows of 14°F (-10°C). A test year: Lettuce, Mizuna, Turnips, Russian kales, Senposai, Tyee spinach, Tatsoi, Yukina Savoy survived a hoophouse temperature of 10.4°F (-12°C) without rowcover, -2.2°F (-19°C) with. Bright Lights chard got frozen leaf stems.

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Seeking Reader Participation

Your experience with your soils, microclimates and rain levels may lead you to use different temperatures. I’d love to hear from readers if they’ve found my numbers work for them, or if they have a different experience. You can leave a comment here, and it will appear on the website, for others to consider. Or you can fill out a Comment Page and only I will see it, although I’ll pass on the information without your name, if I think others would like to know too.

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Preparing for winter

Rowcover rolling with crank handle.
Photo Rodaew Institute

I’ve also written posts about winter preparations

Getting ready for frost. This post includes info on DIY weather-forecasting, our Frost Prediction checklist, and our Frost Alert Card. Also a link to a 126 page book which includes explanations of freezes and frosts to help us make sense of advice we’ve not understood. FrostProtectionFundamentalsPracticeandEconomicsFAO.pdf

Preparing for Frost and Cold Weather. This post includes our Frost Alert Card, a Frost Predictions checklist of what to do when the first fall frost is expected; how to use sprinklers overnight to stop tomatoes from freezing; four ranges of cold-hardiness (some crops can wait in the garden till it gets colder); and different levels of crop protection, including rowcover, low tunnels, Quick Hoops, caterpillar tunnels and hoophouses (aka high tunnels).

Season Extension and Frost Preparations. This post includes my Season Extension slideshow; the Frost Alert Card and Frost Predictions checklist again; a diagram of our winter double hoop system to hold rowcover in place during the worst weather;

Double hoop system for winter rowcover.
Pam Dawling

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Changing Winter Temperatures

Here’s an article from the Virginia Mercury by Sarah Vogelsong, giving info about changing winter temperatures, particularly later fall frosts in Virginia:

The frozen Potomac River. (Sarah Vogelsong/Virginia Mercury)

Autumn’s first frost is falling later. For farmers, the consequences are wide-ranging

by Sarah Vogelsong, November 3, 2020

Halloween has come and gone. The clocks have been set back. Every evening darkness falls just a little bit earlier.

But for much of Virginia, the first frost still remains elusive.

Over the past century, the average date of the first frost has been moving progressively backward throughout the commonwealth, today landing a week or more later than it did at the turn of the 20th century.

“This is one of the clearest signs of not only the changing climate but … its impact on our systems,” said Jeremy Hoffman, who as chief scientist at the Science Museum of Virginia conducts extensive research on climate change in Virginia. “It’s not just here, it’s everywhere.”

As global temperatures have warmed, largely due to the release of greenhouse gases into the atmosphere, frost seasons have shrunk. The Fourth National Climate Assessment released by the Trump administration in 2018 reported that “the length of the frost-free season, from the last freeze in spring to the first freeze of autumn, has increased for all regions since the early 1900s.”

How the shifts have played out in different states with different geographic, ecological and topographic features varies. Data from the U.S. Environmental Protection Agency show that between 1895 and 2016, the average date of the first fall frost moved back by 7.1 days in Virginia.

On the local level, the changes may be even starker. Estimates of how much the average date has changed vary depending on the time range used and how scientists fit a line to their data points, but in most Virginia cities, they show unmistakable upward trends. Looking at first frost dates between 1970 and 2016, Climate Central, a nonprofit staffed by scientists and journalists, calculated that on average, the first frost today is 5.9 days later in Lynchburg, 8.9 days later in Harrisonburg, 12.8 days later in Roanoke, 15 days later in Charlottesville and 18.5 days later in Richmond. While their data show Norfolk’s first frost occurring about six days earlier on average, Hoffman said that longer-range data going back to 1940 show the first frost moving back by about five days. Still, he cautioned, variation does occur: “Localized things like weather” can “work against that dominant signal in datasets like these.”

First freeze dates for Richmond, 1930-2019. (Jeremy Hoffman, Science Museum of Virginia)

The implications of the shifts in the freezing season go beyond a few more days to enjoy warm weather, say scientists and policymakers. Perhaps most affected are farmers, whose livelihood is intimately tied to fluctuations in both short-term weather and long-term climate.

“Some things you can sort of manage around and some things you can’t,” said Wade Thomason, a professor of crop and soil environmental science at Virginia Tech and the state’s grain crops extension specialist.

For most farmers, the last frost of the year in the spring is the riskier of the season’s two endpoints, falling as it does when most plants are young and more vulnerable to temperature extremes. But ongoing changes in the first frost in the fall also have ripple effects.

“It can be a beneficial thing for some instances. We might get more grazing days for livestock operations in a year,” said Thomason. For some crops, like double-cropped soybeans that are planted following the harvest of another crop — typically a grain like wheat — “it can extend the season.”

Other effects are less immediately apparent. Many wheat farmers who typically plant in mid-October have begun to push back their planting dates to ensure plants don’t grow too quickly during the freezing months, making them susceptible to disease or falling over in the field. Specific types of forage rely on long periods of cool weather to thrive: in Northern Virginia and the Shenandoah Valley, farmers have noticed that orchard-grass stands are only living for four to five years instead of the once-standard 10.

“For years now, we’ve heard from farmers that the stands don’t persist like they used to,” said Thomason. Research has shown that one factor contributing to less persistence is warmer nighttime temperatures, he added, but because most operations rely on cultivars developed decades ago, “we haven’t adapted orchard grass that thrives in a warmer climate.”

Other crops affected by longer warm seasons? Tree fruits and wine grapes

“Virginia’s one of those places that we expect to get hotter and we also expect to get wetter,” said Benjamin Cook, a climate scientist with the National Aeronautics and Space Administration’s Goddard Institute for Space Studies whose research includes the effects of climate change on vineyards. Neither of those conditions are necessarily good for high-quality wine prospects, he said. Furthermore, farmers working in these areas face special risks because of the long time to maturity of their crops.

“Those are parts of the agricultural world that adaptation eventually becomes a lot more challenging, because you can’t switch crops from year to year,” he said. “You have to make a bet on something and wait four years to see if it pays off.”

Regardless of their specialty, all farmers face another consequence of shorter freeze seasons: more weeds and more pests.

“With longer growing seasons, with these warmer winters, the populations of insects are increasing, the mortality is lower, they can produce more generations a year, and that potentially presents a problem for agriculture and plants in general,” said Cook.

Those effects can be seen on the ground, said Thomason: “Maybe 30 years ago, we could stop worrying about them in early October, and now it may be a week or 10 days later.”

https://www.virginiamercury.com/ Virginia Mercury is part of States Newsroom, a network of news outlets supported by grants and a coalition of donors as a 501c(3) public charity. Virginia Mercury maintains editorial independence. Contact Editor Robert Zullo for questions: [email protected] Follow Virginia Mercury on https://facebook.com/thevirginiamercury and https://twitter.com/MercuryVirginia

Our stories may be republished online or in print under Creative Commons license CC BY-NC-ND 4.0. We ask that you edit only for style or to shorten, provide proper attribution and link to our web site.

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Root Crops in November

Root Crops to Plant in Central Virginia in November

We have reached the slow-growing time of year. We have passed our last chance to sow root crops outdoors. Nothing changes fast. Reread Root Crops in October for more ideas, if you are in a warmer climate zone than us. We are in Winter-hardiness zone 7, which has overall minimum average of temperatures of 0° to 10°F (-18°C to -12°C). We are in subzone Zone 7a, with a minimum average temperature of 0° to 5° F (-18°C to -15°C).

In late November, we sow our fourth radishes in our hoophouse. See Root Crops in September for more about our succession of hoophouse radish sowing dates. We sow Easter Egg, and White Icicle. It is too late for us to sow Cherry Belle or Sparkler types – they get too fibrous. This sowing will feed us for the month of February. Unlike the late October sowing which lasts for 8 weeks, this sowing will only be good for 4 weeks.

See Root Crops in September for information on figuring sowing dates for winter hoophouse succession crops (radishes are the example)

Late September in our hoophouse: radishes, scallions and new transplants in the beds on either side. Photo Wren Vile

In early November (around 11/9), we often sow our second of three plantings of hoophouse turnips. We sow Hakurei, Early White Egg, Oasis, and Red Round. These will be harvested 2/25-3/10 (with thinnings for greens from 1/11).

Sometimes we make our second sowing in late October, if we have space available then and want bigger turnips. We may make a third turnip sowing in very early December if space opens up then. The third sowing is only worthwhile if thinned promptly and eaten small, as the plants will start bolting in early March.

See Root Crops in October, for details of thinning and harvesting.

Root Crops to Harvest in Central Virginia in November

Large Smooth Prague celeriac.
Photo Southern Exposure Seed Exchange
Florence bulb fennel. Photo
Southern Exposure Seed Exchange

 

 

 

 

 

 

If you are unsure how soon temperatures will drop in your area, see Weatherspark

Enter your city, airport or zipcode and you’ll get access to helpful graphics on seasonal temperatures, cloud coverage, rainfall, snow, sunshine, humidity, wind, water temperature at nearby large bodies of water. Also tourism, which I had not previously thought of as a type of weather! After that comes an assessment of growing conditions (considered only as days without frost) and growing degree-days, solar energy, and more.

In Louisa County, where we are, the average daily low temperature in November makes a precipitous but erratic slide from 45°F (7°C) to 36°F (2°C), with a small chance of going as low as 24°F (-4°C) by the end of November. Most of our root crops other than sweet potatoes and potatoes can wait to be harvested until late November, but we would rather proceed with harvesting and storing, as the daylight gets shorter and the chance of cold, wet working conditions get higher.

Green kohlrabi.
Photo Small Farm Central

 

We continue clearing root crops outdoors and storing them (in this order): 

  • ·         25°F/-4°C, bulb fennel
  • ·         20°F/-7°C, turnips, winter radish, celeriac
  • ·         15°F/-9°C, kohlrabi, beets (15-20°F/-9 to -7°C, depending on variety)
  • ·         12°F/-11°C, carrots, Cylindra beets
  • ·         10°F/-12°C, parsnips, probably OK to 0°F (-18°C)
  • ·         Horseradish is not killable by cold temperatures, as far as I can tell. But if the ground is frozen, you can’t dig it up.

Wash and store roots in perforated plastic bags under refrigeration, or in a root cellar or other cold storage place.

Our 9/6 sowing of hoophouse radishes will have finished and our second sowing will mature and brighten our meals from 11/6 to 12/25 approximately. Our first sowing of hoophouse turnips (10/15) will produce edible little roots as thinnings later in the month.

See Washing, sorting and storing root crops in Root Crops in September.

See my list of Winter-Kill Temperatures of Cold-Hardy  Vegetables 2020 for a more complete picture of “Harvesting in Time”

Other Root Crop Tasks in Central Virginia in November: Long term storage of sweet potatoes and white potatoes

Sweet Potatoes in storage.
Photo Pam Dawling
Sweet potatoes

After curing, store boxes of sweet potatoes at 55-60°F (13-15.5°C), 50-60% humidity. Curing is complete when the skin is undamaged after rubbing two together. If the heating in your curing space is variable, be sure to check several boxes of sweet potatoes closer to and further from the heater. We once had a sad thing happen after a new heater had been installed. We were checking the most accessible boxes only, not the ones at the back near the heater. We got wrinkly sweet potatoes. If your crop is not curing as fast as you hoped, check the temperature, and do what you can with fans to move the air around without blasting directly on any particular box. Also check the humidity and adapt as needed. We found that splashing water directly on the concrete floor of our basement was the most successful method.

 

Restack the boxes (in a rodent-proof storage cage, if you are using an outbuilding).

Peruvian (“white”) potatoes

 

Potatoes stored in crates in our root cellar.
Photo Nina Gentle

Sort white potatoes in storage 2 weeks after harvest. See Root Crops in August

Root Cellar: Cool to 50°F (10°C) after one month, then 40°F (4.5°C), airing once a week or less if cooling not needed. See Special Topic for July

Special Root Crop Topic for November in Central Virginia Vegetable storage without electricity.

  • ·         Meeting the storage requirements of various crops helps maximize their season of availability
  • ·         Some vegetables need to cure before storage and the curing conditions are different from those needed for storage. Curing allows skins to harden and some of the starches to convert to sugars.
  • ·         Many crops may be stored without electricity, perhaps in buildings that serve other uses at the height of the growing season.

  • ·         Washington State University Extension’s Storing Vegetables and Fruits at Home, is a good introduction to alternatives to refrigerated storage, using pits, clamps and root cellars. Drawings below are from WSU Storing Vegetables and Fruits at Home
  • ·         Also old versions of the USDA Agriculture Handbook 66.
Home vegetable storage options, from WSU
Four Sets of Storage Conditions

 By providing storage spaces with 4 types of conditions, 25 crops can be stored.

  • ·         In my chart in Sustainable Market Farming, the Summary column indicates the general conditions needed for each crop, and allocates each crop to one of 4 groups:
  • ·         A= Cold and Moist: 32°F–40°F (0°C–5°C), 80%–95% humidity — refrigerator or winter root cellar conditions. Most roots, greens, leeks
  • ·         B= Cool and Fairly Moist: 40°F–50°F (5°C–10°C), 85%–90% humidity — root cellar. Potatoes
  • ·         C= Cool and Dry: 32°F–50°F (0°C–10°C), 60%–70% humidity — cooler  basements and barns. Garlic and onions
  • ·         D= Warm and Dry to Fairly Moist: 50°F–60°F (10°C–15°C), 60%–70% humidity — basements. Sweet potatoes and winter squash.
Our winter squash storage cage. Photo Twin Oaks Community
Winter squash and pumpkins – storage

We built a rodent-proof cage with wood shelves. You could use shallow crates to avoid handling each individual squash.

In-ground protected vegetable storage. WSU
In-ground storage

Depending on the severity of your winter, some cold-hardy root crops (turnips, rutabagas, beets, carrots, parsnips, Jerusalem artichokes and horseradish) and also leeks can be left in place in the ground, with about 12” (30 cm) of insulation (straw, dry leaves, chopped corn stalks, or wood shavings) added after the soil cools to “refrigerator temperatures.”

 Hooped rowcovers or polyethylene low tunnels can keep the worst of the weather off. There could be some losses to rodents, so experiment on a small scale the first winter to see what works for you. We have too many voles to do this with carrots or turnips.

Besides being used as a method for storage of hardy crops deep into winter, this can be a useful method of season extension into early winter for less hardy crops such as beets, celery and cabbage, which would not survive all winter this way. Access to crops stored in the ground is limited in colder regions — plan to remove them all before the soil becomes frozen, or else wait for a thaw.

Vegetable storage clamp WSU
Storage clamps (mounds)
  • Cabbage, kohlrabi, turnips, rutabagas, carrots, parsnips, horseradish, Jerusalem artichokes, salsify and winter radishes (and any root vegetables that can survive cold temperatures) can be stored with no electricity, by making temporary insulated outdoor storage mounds (clamps).

Mark a circular or oval pad of soil, lay down straw, pile the roots up, cover them with straw and then with soil, digging a drainage ditch round the pile. For ventilation, leave a tuft of straw poking out. Slap the damp soil in place to protect the straw and shed rainwater.

For the backyarder, various roots can be mixed, or sections of the clamp can be for different crops. Those growing on a large scale would probably want a separate clamp for each crop. It is possible to open one end of a clamp or pit, remove some vegetables, then reseal it.

 There is a balance to be found between the thermal buffering of one large clamp and the reduced risk of rot that numerous smaller clamps provide.

WSU vegetable storage in a buried bin.
Pits and trenches

Dig a deep, wide pit (3+ feet deep) in a dry area where water will not stand, lining it with heavy plastic and straw. Alternate layers of vegetables with layers of straw, finishing with straw. Put a loose sheet of plastic on top, (not sealed down). Cover with more soil.

To deter rodents, bury large bins such as (clean) metal trashcans, layer the vegetables inside with straw, and cover the lid with a mound of more insulation and soil.

Or bury insulated boxes in the ground inside a dirt-floored shed or breezeway. A new life for discarded chest freezers! Insulated boxes stored in unheated areas need 6-8” (15–20 cm) of insulation on the bottom, sides and top.

Root Cellars for crops needing cool, damp conditions

  • ·         Potatoes do best in a dark cellar, at 40° – 50°F (5° -10°C). With a good in-ground root cellar, potatoes store for 5-8 months. Ventilate as needed, to maintain the cellar in the ideal range.
  • ·         Below 40°F (5°C) the starches convert to sugars, giving potatoes an unpleasant flavor and causing them to blacken if fried.
  • ·         Root cellars can be used for apples, cabbage, or root vegetables, but be careful what you mix.
  • ·         Some people pack the unwashed roots in boxes of sand, wood ash, sawdust or wood chips. Perforated plastic bags or crates are easier.
  • ·         Pepper plants can be hung upside down in a cellar to ripen, or store. Cabbage can also be hung upside down.
  • ·         Cabbage, celery, leeks can be replanted side by side in boxes or tubs of soil.
Our root cellar for potatoes. Photo McCune Porter
Ethylene

Ethylene is generally associated with ripening, sprouting and rotting. Some crops produce ethylene gas while in storage — apples, cantaloupes and ripening tomatoes all produce higher than average amounts. Environmental stresses such as chilling, wounding and pathogen attack can all induce ethylene formation in damaged crops. Some crops, including most cut greens, are not very sensitive to ethylene and so can be stored in the same space as ethylene-producing crops. Other vegetables, however, are very sensitive to the gas and will deteriorate in a high-ethylene environment. Potatoes will sprout, ripe fruits will go over the top, carrots lose their sweetness and become bitter.

 

Vegetable harvests, articles on seed saving and garlic planting, workshop on cover crops.

 

Close up of Cow Horn okra pods.
Photo Kathryn Simmons

There are several aspects of vegetable harvesting. In this post I will look first at maturity indicators, then at four ranges of cold-hardy crops for harvest at various stages of winter, followed by a reminder of the order for harvesting storable crops, according to the coldest temperature they can take. After that I have links to a couple of other websites with great information on these topics, a mention of two articles on seed saving  and one on garlic planting I have in Growing for Market magazine. And a link to a Mother Earth News Fair Online workshop on establishing winter cover crops.

Harvest and Maturity Indicators

Don’t harvest too soon or too late. How do you know when it’s ready to harvest? Different factors are important for different crops. Use all your senses.

  • Size: Cow Horn okra at 5”/13 cm (others shorter), green beans a bit thinner than a pencil, carrots at whatever size you like, 7”/18 cm asparagus, 6”/15 cm zucchini
  • Color: Garden Peach tomatoes with a pink flush. The “ground spot” of a watermelon turns from greenish white to buttery yellow at maturity, and the curly tendrils where the stem meets the melon to turn brown and dry. For market you may harvest “fruit” crops a bit under-ripe
  • Shape: cucumbers that are rounded out, not triangular in cross-section, but not blimps. Sugar Ann snap peas get completely round before they reach peak sweetness.
  • Softness or texture: eggplants that “bounce back” when lightly squeezed, snap beans that are crisp with pliable tips. Harvest most muskmelons when the stem separates easily from the fruit (“Full slip”).
  • Skin toughness: storage potatoes when the skins don’t rub off, usually two weeks after the tops die, whether naturally or because of mowing.
  • Sound: watermelons sound like your chest not your head or your belly when thumped. Try the “Scrunch Test” – press down firmly on the melon and listen and feel for the separation of the ripe flesh inside the melon.

Cabbages are fully mature when the head is firm and the outer leaf on the head is curling back. Ignore the separate “wrapper leaves” when making this judgment. If you need to keep mature cabbage in the ground a few days longer, twist the heads to break off some of the feeder roots and limit water uptake, and they will be less likely to split.

Mature cabbage showing curled leaf on the head.
This educational photo of a split cabbage is provided by Firesign Farm

Broccoli
Select blue-green broccoli heads and harvest them before the flower buds open, but after they’ve enlarged. We press down with finger-tips and spread our fingers to see if the head is starting to loosen.

Young immature broccoli head after rain
Photo Wren Vile

Sweet Corn

Sweet corn will be ready to harvest about three weeks after the first silks appear. Corn is ready when the ears fill to the end with kernels and the silks become brown and dry. An opaque, milky juice will seep out of punctured kernels. You can use your thumbnails to cur through the husk on the side and view the kernels. Don’t make your cut on top of the ear, or the dew and rain will get in and rot the corn.

Sweet corn ears are mature when the silks die and turn brown. Photo Kathryn Simmons
Mature Sweet corn ear.

Garlic

Garlic is ready to harvest when the sixth leaf down is starting to brown on 50% of the crop. See Ron Engeland’s Growing Great Garlic. Harvesting too early means smaller bulbs (harvesting way too early means an undifferentiated bulb and lots of wrappers that then shrivel up). Harvesting too late means the bulbs may “shatter” or have an exploded look, and not store well.

Cut across hardneck garlic – airspaces around the stem show maturity

Music garlic cut open showing gaps around stem – a sign of maturity.
Photo Southern Exposure Seed Exchange
Garlic bulb cut horizontally to check maturity (good now or soon).
Photo Wren Vile

Onions

Wait until the tops fall over to harvest, then gently dig up the whole plant and dry. Leave the dry, papery outer skin on the onion for protection.

Onions curing and drying in strings. Photo by Southern Exposure Seed Exchange

Four Ranges of Cold-Hardy Crops for Harvest at Various Stages of Winter

  1. Crops to keep alive into winter to 22°-15°F (-6°C to -9°C), then harvest. Harvest and use soon: Asian greens, broccoli, cabbage, chard, lettuce, radishes. Harvest and store: beets, cabbage, carrots, celeriac, kohlrabi, winter radish (including daikon), rutabagas, turnips. Many greens and roots can survive some freezing, so it is worth experimenting to find how late you can keep crops outdoors.
  2. Hardy winter-harvest crops: cabbage (Deadon), carrots, collards, kale, leeks, parsnips, scallions, spinach. We grow our winter-harvest crops in our raised bed area, which is more accessible in winter and more suited to small quantities.
  3. Overwinter crops for spring harvests before the main season. Some crops, if kept alive through the winter, will start to grow again with the least hint of spring weather and be harvestable earlier than spring plantings. Depending on your climate, the list can include carrots, chard, chicories such as radicchio and sugarloaf, chives, collards, garlic, garlic scallions, kale, lettuce, multiplier onions (potato onions), scallions, spinach. In mild areas, peas can be fall sown for a spring crop. Sow 1″ (2.5 cm) apart to allow for extra losses.
  4. Winter hoophouse crops: The rate of growth of cold-weather crops is much faster inside a hoophouse than outdoors. The crop quality, especially with leafy greens, is superb. Plants can tolerate lower temperatures than outdoors; they have warmer soil around their roots, and the pleasant daytime conditions in which to recover. Salad greens in a hoophouse can survive nights with outdoor lows of 14°F (–10°C) without inner rowcover.

In my post Root Crops in October, I gave this list of storable crops in the order for harvesting, related to how cold they can survive.

Clear and store (in this order):

  • Sweet potatoes 50°F (10°C)
  • “White” Peruvian potatoes 32°F (0°C) approximately
  • Celeriac 20°F (°C)
  • Turnips 20°F (°C)
  • Winter radish 20°F (°C)
  • Beets 15-20°F (°C)
  • Kohlrabi, 15°F (°C)
  • Carrots 12° F (°C)
  • Parsnips 0°F (°C)

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Here are some links to a couple of good sources for more harvest information:

  1. Piedmont Master Gardeners Garden Shed Newsletter

Guidelines for Harvesting Vegetables by Pat Chadwick

A list of seven basic principles of harvesting, followed by a crop-by-crop list of almost 50 individual crops and a resource list of 18 publications (focused on the mid-Atlantic and Southeast)

  1. October Tips from Harvest to Table, by Steve Albert covers all climate zones and comes complete with a USDA Hardiness Zone Map

Prepare your garden for colder weather, plant winter crops where there is still time, harvest crops that will suffer from cold, construct low tunnels with rowcover or clear plastic to keep crops somewhat protected from wind and cold temperatures

Links to other posts by Steve Albert

How to Prepare a Winter Vegetable Garden

Predicting Frost in the Garden

Garden Tips for October


Growing for Market articles

Harvesting seeds this fall?

I have written articles for Growing for Market magazine about growing and saving seeds (August and September issues), and planting garlic (October issue).

Given the shortages of some varieties this spring, it wouldn’t surprise us if more people tried producing seeds of vegetable or flower varieties this year. Here are links to articles from the August and September magazines, covering wet and dry seed processing.

Roma tomatoes cut in half for seed extraction.
Photo Pam Dawling

Wet seed processing and saving

Wet seeds are embedded in fruit. Wet processing has four steps: scooping out the seeds or mashing the fruit, fermenting the seed pulp for several days, washing the seeds and removing the pulp and then drying the washed seeds.

Read the article “Wet seed processing and saving”

Dry seed processing and saving

Dry seeds develop in pods, husks or ears, and dry on the plant rather than inside a fruit. While you obviously want to get seeds into the hands of growers before they need to plant, and into seed catalogs before they get printed, often there is no urgency to extract the dry-seeded crops from their pods. You can wait for a slower time, or use seed cleaning as a rainy-day job.

Read the article “Dry seed processing and saving”

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Mother Earth News Fair

I have a workshop on Winter Cover Crops for Gardeners as part of the Mother Earth News Fair Online Winter Gardening Course. The Winter Gardening Course features 7 videos, each 21-44 minutes long. Mine’s 32 minutes on cover crops.

You can enroll for the 8-course Winter Gardening Course for $20.

Or choose the 2020 all-access course bundle of 21 courses (over 100 videos) for $150.

 

 

 

 

 

 

 

 

 

 

Sweet potato harvests over the years

Crew harvesting sweet potatoes. Photo Wren Vile

 In my 10/30/20 post Growing High Yielding Sweet Potatoes, I wrote

When to harvest sweet potatoes

Unlike white potatoes, which have the annual plant sequence of vegetative growth, flowering and dying back, sweet potato plants would go on growing forever if the weather remained warm enough. Choose when to dig them up, ahead of cold weather. The longer you wait, the bigger the potatoes, but you are gambling with the weather. Usually sweet potatoes are harvested in the week that the first frost typically occurs in your region. I have written plenty already in previous years about harvesting, so I won’t go into it here. See one of the links to those posts, or my slideshow, if you want to know what comes next, or your climate is considerably colder than mine in central Virginia.

Today I looked to see the “plenty” I had written in previous years, and was surprised not to find much! Every mid-October from 2012 to 2016, I mentioned sweet potato harvest, but many times it has been in passing, and mostly yield statistics (bragging or groaning). 2012 has the most detail on doing the harvest – read it below.

In 2019 we got a very nice yield and carried on eating sweet potatoes into September. Previously people seemed to lose interest in sweet potatoes in late May, and we would distribute our surplus to other people. This year we just kept eating and enjoying them. I can report that they did get wrinkly and grow big sprouts, but were still very tasty down to the last one in late September.

We now use electric fencing to keep the deer out, and grow on biodegradable plastic mulch to keep the weeds down, and use drip irrigation to grow the sweet potatoes up. These developments in our method became necessary over the years.

Yesterday we ate sweet potato leaves as a seasonal green. You can eat these throughout the growing season, but we usually don’t, as we hesitate to take away anything that is helping the tubers grow. But at harvest time, the leaves are about to return to the soil, so we clipped the vine tips and cooked them up. OK, interesting, never going to be a favorite for me, but perfectly acceptable, and less distracting than going off to harvest somehting else to eat in the middle of the big sweet potato harvest!

Sweet potatoes ready to crate up.
Photo Nina Gentle

Sweet Potato Harvest October 2016

10/11/16: Yesterday we started harvesting our sweet potatoes. Yields look OK but not fantastic. We had a lot of problems with deer eating our sweet potatoes this year. We did have a temporary electric fence, but we often didn’t pay it good attention and it grounded out. Next year the rotation brings the sweet potatoes to a more traveled location. I can’t believe I’m already doing that “Gardener Survival Strategy” of thinking “Next Year Everything Will Be Perfect”!!

 10/18/16: Our average first frost date is October 14. Actually from our own records it has averaged 10/22 over the last 11 years. . . .  It’s good to be prepared.

This post includes tips on DIY weather-forecasting, and preparations for fall frosts

Sweet potatoes sorted into boxes.
Photo McCune Porter

 Sweet Potato Harvest 2015

 10/20/15: We got our sweet potatoes all dug and safely indoors before Saturday night’s 27F and Sunday night’s 26F. Whew! Another Garden Year Milestone passed. We got about 223 boxes this year. The boxes contain about 23lbs each, so that’s 5129 lbs, plenty to feed 100 hungry people for six or seven months. . . .  Our average harvest for this size patch (about 700 plants) is 4035lbs. This year we got a yield of a little over 7lbs of sweet potatoes per plant. Last year’s record crop was 11lbs per plant.

 10/13/15: We are on the point of harvesting our sweet potatoes. After all the rain we had recently, we were waiting for the soil to dry enough to walk on. . . . I was worried for a couple of days that the weather would stay cold and the sweet potatoes might rot in the cold wet soil. One year when I was fairly new to Virginia I caused us to leave the sweet potatoes in the ground till early November (hoping they would grow a bit more) and then it rained hard and we ended up with a load of sweet potatoes that either rotted directly or else went through a transition to a hard uncookable state. I learned the hard way to harvest sweet potatoes before soil drops to 55F. This week I studied the soil thermometer and the max and min thermometer and was reassured by the warm sunny days. The soil has been drying out nicely. Tomorrow we start digging. It usually takes us three afternoons. Everything looks auspicious. No rain or horribly cold weather, enough people. . .

Crates of sweet potatoes selected for growing next year’s slips.
Photo Nina Gentle

Sweet Potato Harvest 2014

10/14/14: Our sweet potato harvest is huge this year! We mostly managed to keep the deer out of the plot, by luck and a scarecrow and things that fluttered in the breeze. We’ve filled all our usual boxes and then scrambled twice to find more! . . . . I counted the equivalent of 273 normal-sized boxes in the basement this morning. At 23 pounds for our standard box, that’s about 6280 pounds. We might be up to 6500 pounds by the time we’re done. This will be our record! I think our local food pantry will be getting some sweet potatoes this winter and next spring!

I compared sweet potato yields for different years. We usually have about 600 plants in 800 row feet (16″ spacing). Yield is about 11 pounds/sweet potato plant this year. But as they say “your results may vary.”  Ours certainly have. Working back from 2012, we harvested 4070 lbs, 2208 lbs, 1860 lbs, “lots” (poor record-keeping!), 5590 lbs, 3820 lbs and 4050 lbs in 2007.

Hauling sweet potatoes uphill the hard way. Sometimes we use the truck!
Photo Nina Gentle

Sweet Potato Harvest 2013

10/13/13, Sweet potatoes, statistics and inspiration: After a week of drizzle, it finally eased up and we started harvesting our sweet potatoes. . . .  As usual, we set the dug roots in clusters, so we could see which plants yielded most and chose medium-sized roots from those to grow our slips next year. . . . This year, the Georgia Jet seem more productive than the Beauregard – I think that’s usual. We dug about a third of the crop the first day and got 86 boxes. The second day we had a lot of other harvesting (beans and broccoli being the most time-consuming), so we only dug another 36 boxes. . . .

Well  . . .  the yield dropped off a lot where the deer had been browsing (memo: fence out the deer in future!) We got a total of 177 boxes of various sizes, perhaps about 3939 pounds, almost two tons. . . .

Our yearly harvest of sweet potatoes has varied a lot, from 31 boxes (a sad year) to 243 in 2009. An average over ten years of 112 boxes, each weighing perhaps 23 pounds. . . .  We always hope to have enough to last till the beginning of May, when people start to lose interest in sweet potatoes, and start hoping for tomatoes.

Sweet potato harvest.
Photo Nina Gentle

How we do our Sweet Potato Harvest 2012

10/12/12: Usually sweet potatoes are harvested the week the first frost typically occurs. . . . Contrary to myth, there is no toxin that moves from frozen leaves down into the roots. On the other hand, cold injury can ruin the crop, and roots without leaf cover are exposed to cold air temperatures, and have lost their method of pulling water up out of the soil. Cold wet soil can quickly rot sweet potatoes (I know, it’s happened here).

To harvest, we first remove the vines from the area to be harvested that day. There is usually 3 afternoons’ digging for ours, and we want to leave live vines to protect the rest of the crop overnight. We use pruners to snip the vines where they emerge from the soil, leaving stumps to show where to dig. We roll the vines into the spaces between the rows.

Using digging forks, we carefully dig up the roots, which grow in the ground in a bunch-of-bananas shape. We want to select good potatoes for seed, and we grow several different kinds (Georgia Jet, Beauregard, and a couple of heritage varieties whose names we don’t know), so we make sure not to mix potatoes from different rows. As we dig, we set the potatoes out beside the spot where they’ve grown, one clump per plant, so it’s easy to identify the most productive plants.

It’s important not to bruise the roots, or to leave them exposed to temperatures higher than 90°F (32°C) for more than half an hour, or they will get sun-scald. Below 55°F (13°C), they’ll get chilling injury. We also avoid any abrasion of the skin, which is very fragile at this stage. We leave the sweet potatoes to dry on the ground for 1-2 hours, unless the weather is unsuitable. This year we had ideal weather, not too hot, not too cold, breezy enough to dry the skins, sunny.

We want to grow our own slips (baby plants) next year, so we save at least 1 root per 5 slips wanted.  (1 good slip every 16″.) So to plant 800 row feet, (600 slips), we save 100 each of our two main varieties and 20 each of the two heirlooms. That should be plenty. Some will shrivel or rot, so we allow a margin. We don’t save for seed any roots that look diseased. We choose plants with a high yield and no string (rat-tail) roots. From these plants, we choose small-medium sized potatoes with typical shape and color.

When grading and crating the roots in the field, we first choose the seed potatoes, and then sort storable from “Use First” roots. Large open broken surfaces will cure and can be stored, but any roots with soft wet damaged areas or deep holes (whether from voles, bugs or fork tines) will not store, and should be graded out, for composting or immediate use. We sort into 4″ deep wood flats or 5″ plastic crates for curing, and buckets for the “Use First” category.

Boxes of sweet potatoes curing.
Photo Nina Gentle

Immediately after harvest, we take the boxes of sweet potatoes into a warm damp basement below the dining hall, to cure. This allows the skin to thicken, cuts to heal over and some of the starches to convert to sugars. Uncured “green” sweet potatoes are not very sweet at all, and are better used in dishes where they combine with other foods. A baked uncured sweet potato is a sad disappointment.

We stack our boxes of roots on pallets, and put wooden spacer sticks between boxes in each stack, to ensure airflow. We get quite good temperatures, but keeping humidity up is difficult for us. We cover the flats with newspaper to hold in some moisture. The best result seems to come from splashing water on the concrete floor several times each day. We use box fans to improve the airflow, and the basement already has some natural ventilation.

Ideal conditions for curing are 85-90°F (29-32°C), and 80-95% humidity for 4-7 days, with some airflow and ventilation. Curing takes longer if conditions are less than perfect. The length of the curing period also varies with the dryness of the soil just prior to harvest. We usually reckon on 10-14 days. . . . .

So – how did we do this year? Middle of the road, I’d say. Decent yields, but not a bumper crop – we still had empty boxes left over. The deer were regularly eating our vines until quite recently. Last year we had a dog to chase the deer off, but he met with a road accident. His replacement was old, and she just wanted to be a pet, so we had deer again. We used drip irrigation and biodegradable plastic mulch this year, and did a good job of weeding, so I put the lower yields down to deer damage.

Sweet potatoes on a plate.
Photo Brittany Lewis

Root Crops in October

Radish Quick Pickles
Photo by Bridget Aleshire

Root Crops to Plant in Central Virginia in October

We have now passed our last chances to sow root crops outdoors. But the exciting season in the hoophouse has just begun. In early October, we sow radishes in our hoophouse. See Root Crops in September for more about our succession of hoophouse radish sowing dates. We like Easter Egg (a multi-colored mix of red, plum, pink, purple and white varieties, that matures over several weeks), Cherry Belle, the fast, uniform red globes, and White Icicle, like baby daikon about 3” (7 cm) long. These three varieties all stay crunchy and tender. We have a dread of fibrous radishes! Most years we make a sowing at the beginning of October and another at the end, and these will feed us from early November until early February. The late October sowing lasts for 8 weeks, so it’s good to make sure we plant enough. Radishes do a lot to brighten up meals in December and January!

White Egg Turnips.
Photo Southern Exposure Seed Exchange

In mid-October (10/10-10/25), we sow our first of three plantings of hoophouse turnips. We like the very fast-growing and tender Hakurei hybrid. It has short hairless tops which also make good eating. We sow this variety on the south side of the bed, leaving the other 3 rows for the taller varieties. We also like Early White Egg and Oasis, which are not quite as uniform as Hakurei, but are OPs and the seed is much cheaper. They produce more greens, which we value too. In the north row we often grow Red Round, a beautiful red-skinned turnip with tall attractive leaves. We also like Scarlet Ohno Revival, which has the advantage of hairless leaves. This is an Open Source Seed Initiative variety. The OSSI pledge: “You have the freedom to use these OSSI-Pledged seeds in any way you choose. In return, you pledge not to restrict others’ use of these seeds or their derivatives by patents or other means, and to include this pledge with any transfer of these seeds or their derivatives.”.

We thin the turnips as needed. If we sowed thickly, the first thinnings become baby greens for salad. Once the turnips are the size of marbles, we like to thin the plants to 3” (7 cm) apart and cook them whole, roots and greens together. The next thinning is to 6” (15 cm) and from that point on, we harvest the greens and roots separately. We get a ratio of one bucket of roots to two buckets of greens, which fits our needs perfectly. We like to mix the roots, as the one quarter of red roots adds a pop to the appearance.

Root Crops to Harvest in Central Virginia in October

Misato Rose Winter Radish.
Photo Southern Exposure Seed Exchange

We can continue harvesting beets (and beet greens), carrots, horseradish, kohlrabi, radishes, turnips (and turnip greens), and winter radishes outdoors. Once we have had a decisive frost we can harvest parsnips – the frost really improves the flavor. Our 9/6 sowing of hoophouse radishes will start to mature.

See Washing, sorting and storing root crops in Root Crops in September

We tackle our process of clearing root crops and storing them, starting with celeriac (if we grew it this year). We start with the least cold tolerant roots and work our way to the most cold tolerant. This list is root crops only. See my list of Winter-Kill Temperatures of Cold-Hardy Winter Vegetables 2020 for a more complete picture of “Harvesting in Time”

Clear and store (in this order):

  • Sweet potatoes 50°F (10°C)
  • “White” Peruvian potatoes 32°F (0°C) approximately
  • Celeriac 20°F (°C)
  • Turnips 20°F (°C)
  • Winter radish 20°F (°C)
  • Beets 15-20°F (°C)
  • Kohlrabi, 15°F (°C)
  • Carrots 12° F (°C)
  • Parsnips 0°F (°C)
Bucket lid with holes for sorting root vegetables for storage.
Photo Wren Vile
  • Wash, and store roots in perforated plastic bags in refrigerator or root cellar. We use a special measuring bucket lid to help new workers determine if roots are big enough to store.
  • Harvest sweet potatoes before soil temperatures go much below 55°F (13°C), or night air goes below 50°F (10°C). See the Special Topic below.
  • Harvest white potatoes when the skins have thickened. (When the skin is undamaged after rubbing two together. About 2 weeks after the  tops die). See Harvesting Potatoes and Root Crops in June. Two or three days before harvesting, we spend the day removing the hay mulch from our 1600 row feet (488 m) potato patch to the compost area. Our potato digging machine can’t deal with mulch or heavy weeds. To fit with using machinery, we clear complete rows. We have a Perfect Potato Harvest Checklist. For fall harvesting we do the tractor work in the morning and pick up the potatoes in the afternoon, avoiding leaving any out overnight if it will be frosty. (When harvesting the March-planted potatoes in July, we do the tractor work early in the morning and start picking up the potatoes as soon as possible. We aim not to be outdoors after lunch when it’s hot, but if we need to, we will, as we don’t want ready-baked potatoes sitting on the soil!) Tractor time is 4 hrs x 2 people. Picking time is 30 people-hours.
  • For beets, we allow 6 people-hours per bed (360 row feet (110 m), and expect 2-3 50-pound (23 k) bags per bed. Cut the stems about ¼” (6 mm) above the root, to reduce “bleeding” when you cook the beets. I was reminded recently that not everyone knows that the easiest way to cook beets is to scrub them, boil them in the skins, drain and immerse in cold water, then simply slide the skins off. Hardly any wasted food and no wasted time.
  • Bucket of freshly harvested Detroit Dark Red beets for storage.
    Photo Pam Dawling
  • For carrots, we allow 4.5-6.5 people-hours per (large) garden cart for washing, trimming and sorting. Plan to keep the last 15 minutes for clean-up. Divide the rest of the time available by 3. Use 1/3 of the time for digging, 2/3 of the time for washing and sorting. Add time to take to storage. Record yields. We take the carrot tops back and spread them across the beds. (fall harvest only ). In the spring and summer we take carrot tops to the compost pile, as the smell can attract carrot rust root flies. In late fall it is too late to sow cover crops to protect the soil, and the flies have gone to overwinter wherever they do that, so we spread the tops over the beds to provide some protection for the soil.)
Carrot rust fly damage (or possibly carrot weevil) Photo Jessie Doyle
Carrot pest larvae: carrot rust fly I think. Maybe carrot weevil.
Photo Jessie Doyle

Special Root Crop Topic for October in Central Virginia:

Harvest sweet potatoes

Here’s our method:

First roll up the drip tape. Harvest on 3 mild days – generally in the week that your first frost usually occurs (10/7-14). We expect our whole harvest of 800 row feet (244 m) to take 80 people hours. Allow 1/3 of the time for snipping, 1/3 for digging, 1/3 for crating and schlepping. Digging takes a bit less time than either of the other jobs. Even a few hours exposed to temperatures below 50°F (10°C) will cause chilling injury. (Frost on the leaves does not of itself damage the roots). Don’t leave clipped plants uncovered overnight. Don’t leave sweet potatoes outdoors. Clip the vines, dig carefully, set the tubers in plant-clusters to dry on the soil. Select seed tubers (healthy med-size tubers from high-yielding plants, no rat-tails).  We save a generous 100 Georgia Jet, 100 Beauregard, 20 each of Bill Shane’s White and Jubilee. (These last two are unofficial names for varieties we were given and are maintaining for genetic diversity.)

Sweet potato harvest.
Photo Nina Gentle

Other Root Crop Tasks in Central Virginia in October:

Curing sweet potatoes and white potatoes

Cure sweet potatoes in collapsible, stackable holey crates (or in wooden flats with spacers for ventilation) and cover with newspaper on top, in a basement with the heater on, for 10-14 days (85-90°F, 27-32°C, 80-90% humidity) or longer if it’s cooler and drier.  Use fans. Splash water on floor. Curing is complete when the skin is undamaged after rubbing two together. Restack the boxes (in a rodent-proof storage cage, if you are using an outbuilding).

Cure freshly harvested white potatoes in a root cellar at 60-75°F (15.5-24°C) for 2 weeks, with good ventilation, then cool cellar to lower temperature. See Special Topic for July. For weeks 2-4, the temperature goal is 50°F (10°C), and fresh air is needed about once a week. Our method of providing an air change in our cellar or adjusting the temperature is to leave the door open when the temperature will be closer to our goal than the current reality. It works well enough.

Planning to grow potatoes again

Planning to grow potatoes again 

Potato plant emerging in spring.
Photo Kathryn Simmons

This is the last part of a monthly series on growing potatoes, a dietary staple.

I have a whole chapter about potatoes in Sustainable Market Farming, where the basics of potato growing can be found. Below are more details about growing potatoes that you may not have wanted or needed this year. Use your own records and this information to plan for bigger harvests, at times of year suited to your farm.

Varieties

Some varieties store better than others, so advance planning will help achieve good results. Scrutinize the small print in the seed catalogs before your next seed order.

Covering a row of seed potato pieces aligned under a rope.
Photo Ira Wallace
Photo Ira Wallace

Potato types: determinate and indeterminate

We have mostly grown Red Pontiac, Yukon Gold and Kennebec. They all seem to be determinate varieties — they grow as a bush, then flower and die. I only learned this year that there are determinate (varieties with naturally self-limiting growth, generally “early” varieties) and indeterminate varieties (such as “Russet Nugget,” “Nicola,” “German Butterball” and “Elba”). The distinction is explained in Potato Bag Gardening. Growers using towers, grow bags, and cage systems want indeterminate potatoes, which continue to produce more layers of tubers on the stems as they are progressively covered with more soil. Growers wanting a fast reliable crop in the field mostly choose determinate types, which grow as a bush, then flower and die. The Internet does seem to have some contradictory statements about which varieties are determinate and which indeterminate, and some dedicated container growers make assertions not supported by experienced commercial growers. So Reader Beware! I trust Extension and here’s a link to their Ask an Expert page on potato types.

Crop rotation, including cover crops

This is very important for potatoes, which are nightshades like potatoes, peppers and eggplant. Colorado potato beetles emerge from the soil in spring and walk (they don’t fly at this stage) towards the nearest nightshades they can detect. Give them a long hike! A distance of 750′ (230 m) or more from last year’s nightshade plots should keep them away. A three- or four-year rotation out of nightshades in each plot is ideal.

Suitable cover crops before potatoes include brassicas (which can help reduce root knot nematodes and Verticillium), Japanese millet (which can reduce Rhizoctonia) and cereals in general. Beware beets, buckwheat and legumes such as red and crimson clovers, and some peas and beans, as these can host Rhizoctonia and scab.

Late corn undersown with oats, mowed high in October to deal with weeds, and the ex-sweet potato patch sown in winter wheat and crimson clover. Credit Ezra Freeman

In our ten year crop rotation, our March-planted potatoes follow a winter of oats and soy (which winter-kill in our zone 7a climate). This cover crop is undersown in our late sweet corn about 30 days after sowing. Our June-planted potatoes follow a winter cover crop mix of winter wheat or winter rye and crimson clover. This mix is sown in early-mid October after our middle planting of sweet corn. (Yes, we risk the clover.) We had read that potatoes are said to do well after corn, so when we set up our crop rotation, that’s what we did. I have no scientific proof that the assertion is true, but we often have good potatoes, so at least it does no obvious harm!

Fall broccoli transplanted after July potato harvest, and undersown with a mixed clover cover crop.
Photo Nina Gentle.

After harvesting our March-planted potatoes in mid-July, we regularly did a fast-turnaround and transplanted our fall broccoli and cabbage in late July. We undersowed that with a clover mix 4 weeks after planting the brassicas. We kept the clover mix for an all-year Green Fallow, right round until the February a year and a half later. This fast-turnaround was a bit nerve-wracking, so we no longer do that, simply following the potatoes with the clover mix, while transplanting the brassicas in another plot.

After harvesting our June-planted potatoes in October, we sow winter wheat or winter rye with crimson clover or Austrian Winter Peas, depending when we are ready to sow. (Wheat and clover if by 10/15, rye and peas if later)

Preparing the Soil

A bed ready for tilling after mowing the cover crop and spreading compost.
Photo Pam Dawling

Potatoes benefit from generous amounts of compost or other organic matter (they use 10 tons/ac, 22,400 kg/ha) and will grow in soils with a pH of 5.0–6.5. They use high amounts of phosphorus (P) and potassium (K), and need adequate soil levels of iron and manganese. They are less affected by low levels of copper and boron. Hay mulch can be a good source of K. As Carol Deppe points out, potatoes will still produce an OK crop in poor soil, where you might not be able to grow much else. See the ATTRA publication Potatoes: Organic Production and Marketing.

Dormancy

See Part 5, Storing Potatoes, for an introduction to this topic. When potatoes sprout and whether they grow one or more sprouts, can be controlled by manipulating the storage conditions.

For extra-early spring planting, aim to sprout relatively few eyes per potato, so that relatively few shoots will grow and the seed pieces will be big enough, with enough nutrients for the plants. Do this by priming the seed potatoes at 65°F (18°C) until the eyes at the rose end just start to sprout. Store at 45°F (7°C) until two weeks before planting time, then finish the sprouting in warmth and light. The early sprouting of the rose-end eyes suppresses the sprouting of the other eyes. If needed, break off extra sprouts before planting.

To avoid sprouting, keep the potatoes below 50F (10C) once they are more than a month from harvest, avoid excess moisture, and avoid “physiological aging” of the potatoes, caused by stressing them with fluctuating temperatures, among other things. If eating potatoes do start to develop sprouts, it’s a good idea to rub off the sprouts as soon as possible, because the sprouting will produce ethylene, which will encourage more sprouting.

Physiological age of seed potatoes

Seed potatoes can act differently depending on their “physiological age.” The warmer the conditions are after dormancy ends, the quicker the sprouts grow and the faster the tubers “age.” When we buy seed potatoes the storage conditions they have already received are beyond our control. As a guide, the length of the longest sprout, and the number of sprouts are measures of physiological age (if the sprouting has taken place in the light). Varieties do not all show these effects to the same degree.

Don’t let your potatoes sprout in storage
Photo Jesse Strassburg

Deliberately adjusting storage temperatures is a way of manipulating the physiological age, in order to get higher yields or earlier maturity. To age seed potatoes, buy the seed in late fall or early winter before they break dormancy and store them rose (eye) end up in daylight at 50°F (10°C) until just before the planting date. In spring, reduce the temperature just before planting, to minimize the thermal shock from the cold soil.

Physiologically “young” tubers will have just one or two sprouts, due to apical dominance (when the leading bud inhibits the other eyes from developing shoots). The plants will have fewer stems, leading to fewer, but larger, potatoes. They will need longer to grow, and so give a later harvest. If you hurry and dig them early, you will only get low yields.

“Middle-aged” tubers give the best yields (27% higher than young or old tubers). “Middle-aged” seed potatoes have multiple short sprouts, without the hairy look of “old” ones. The pre-sprouting instructions given in Part One: Planting potatoes aim to produce “middle-aged” seed.

Physiologically “old” seed potatoes will have many “hairy-looking” branched sprouts, coming from eyes all over the potato. These potato plants emerge faster and start tuber formation sooner. The final plant size will be smaller (because the shoots are weak) and the plants will be more susceptible to drought and die sooner. Because the tubers do mature quickly, they may be good if you seek an early harvest, or are planting a fall crop a bit too close to the frost date. The total yield will be lower (but earlier) than from “younger” seed.

See the University of Maine Extension Service Bulletin #2412, Potato Facts: Selecting, Cutting and Handling Potato Seed  Their drawings are reproduced here. Also see Know and Grow Vegetables by Salter, Bleasdale, et al. for more on this complex topic.

More POTATO resources

The University of Maryland Extension Home and Garden Info Center Potatoes

University of Maryland IPM series on potatoes, which is a troubleshooter sheet on causes and solutions for problems

Cornell 2016 Organic Production and IPM Guide for Potatoes (104 pages)

The Potato Association of America, Commercial Potato Production in North America 2010. (90 pages)

The Government of Canada Biofungicides provide Post-harvest Disease Protection in Potatoes

Other related Blog Posts

Potato Research on Harvest and Storage

What Makes Potatoes Sprout, Nov 2017

How to Deal with Green Potatoes (one of my most-read blog posts!)

Green Potato Myths and 10 Steps to Safe Potato Eating in Mother Earth News

Root Crops in September

 

Root Crops in September

Cherry Belle radishes in the fall.
Photo Pam Dawling

Root Crops to Plant in Central Virginia in September

In September the days get shorter and we get our last chance to plant crops to feed us during the winter. Much more of our garden time will be spent harvesting this month!

In early September we can direct sow several root crops.

  • Daikon and other winter radish (in very early September);
  • Turnips (by 9/15);
  • Kohlrabi only takes 60 days from sowing to harvest. They can be direct sown or transplanted from flats or an outdoor nursery seedbed at the beginning of September. Kohlrabi is hardy to about 15°F (-9.4°C). Our night temperatures will be higher than that until the beginning of November;
  • Small radishes by mid-September. We usually squeeze these in on the south shoulder of a bed of kale, because they grow quickly and we don’t need a whole bedful. By the time the kale needs the space, the radishes will be gone.
  • In the hoophouse, we start our winter crops by sowing radishes and leafy greens on 9/6 or 9/7.
A bed of young growing turnips.
Photo Pam Dawling

See Root Crops in August for more details on these.

It’s too late for any slow-growing crops like carrots. We can just squeeze in some beets at the beginning of September, if we take good care of them. Hoeing, weeding and thinning at the first opportunity will help them grow a bit faster and make up for lost time. We could cover them with rowcover to warm their airspace and soil, once we have got them established and tidied up. I hate to cover weedy crops with rowcover – you just know it encourages weeds to grow faster! Beets won’t die of cold until 12F for my favorite, Cylindra, so they have quite a while yet. See Root Crops in August for more about fall beets.

Radish succession crops

In our winter hoophouse, we sow radishes six or seven times. It is a science and an art to time the sowings to provide a succession of delectable little radishes with no gaps in supply and no overlap of plantings and gnarly big roots. I have made a graph of radish sowing and harvesting dates to help us even out our supply.

Here’s a chart. 1/25 is our last worthwhile sowing date for hoophouse radishes.

Radish #1 sown 9/6 Harvest 10/5 – 11/15
            #2 sown 10/1 Harvest 11/6 – 12/25
            #3 sown 10/30 Harvest 12/16 – 2/7
            #4 sown 11/29 Harvest 1/16 – 2/25
            #5 sown 12/23 Harvest 2/19 – 3/16
White Icicle radishes in our hoophouse in winter. Photo Pam Dawling

Root Crops to Harvest in Central Virginia in September

During September, the root crops we can harvest include beets (and beet greens), carrots, radishes, turnips and horseradish (which I have more to say about below). We hold off on parsnips, if we have grown those, as the flavor improves a lot after a frost.

We could harvest potatoes, which I have written about in Potato Harvesting and Root Crops in June. We hold off on sweet potatoes until October, and I’ll write about them in a post of their own in a few weeks. If you need to harvest earlier, read the chapter in Sustainable Market Farming.

Special Root Crop Topic for September in Central Virginia: Horseradish

Horseradish plant.
Photo Harvest to Table

Horseradish, Armoracia rusticana, a perennial, is very easily propagated from pieces of root. It can be hard to get rid of if you change your mind! It’s wise to plant your perennial food crops in a special place that isn’t part of your annual crop rotation space. Remove all perennial weeds before planting horseradish or any other perennial vegetable. Ours is beside our grape vines, near our rhubarb. Full sun or partial shade will work. Horseradish looks like a big bad dock growing, but is in fact a brassica. Horseradish can provide value-added products for out-of-season sales, as well as a pungent treat in cold weather.

Horseradish root.
Photo GrowVeg

Buy or beg crowns or root pieces, and plant them 4-6 weeks before your average last frost date. Horseradish grows best in cool, damp regions with temperatures between 45°F (7°C) and 75°F (24°C). But in central Virginia, temperatures go from 0°F (-18°C) and 100°F (38°C) and we have more than enough horseradish, so don’t worry too much about that temperature range.

Plant crowns just at soil level. Plant root pieces with the top just below the surface and the bottom end covered with 2-3’ (5-8 cm) of soil. Space horseradish plants 24-36” (60-90 cm) apart. If you are worried about it spreading into important nearby plants, create a metal, wood or stone barrier 24” (60 cm) deep around the bed.

Keep the soil damp, add some compost once a year. You are unlikely to have any pest or disease problems with this crop. Young plants should not be harvested until the leaves are at least 12” (30 cm) long.

Horseradish plant.
Photo Nourse Farms

Horseradish is traditionally harvested September-April (the months with R in them!). The roots go as much as 2 ft (60 cm) deep and are very strong (but not as sturdy as gobo, Chinese burdock). Use a strong shovel, spade or digging fork, and start loosening the roots from 6” (15 cm) away. If you hear or feel a root snap, be glad! The goal is to extract some of the roots and firm up whatever remains, to continue growing. Water the plants after harvest if the weather is dry.

Collect the harvested root parts in a bucket, and wash them right away. You can store them dirty, but it is harder to get them clean later. Harvested roots can be refrigerated for several months until used – they seem fairly impervious to rot.

When you process horseradish do it outdoors, with googles on. I kid you not! This can be a good porch activity in sunny chilly weather. After thoroughly washing and scrubbing the roots, peel them carefully. Throw the peelings in the trash, not the compost pile, as they easily regrow from tiny pieces!

The peeled roots can be ground up in a food processor, to make relish or sauce. Or if you prefer, use a fine grater.

Harvested horseradish roots.
Photo Wikipedia Kren_Verkauf

If you want to buy plants, try Nourse Farms

If you’d like to read more about horseradish, including container plants grown as an annual, there’s info on Harvest to Table

If you’d like to read how to make the condiment, see Barbara Pleasant’s article on GrowVeg

Other Root Crop Tasks in Central Virginia in September: Washing, sorting and storing root crops

Harvesting

How you harvest roots depends on the scale of your farm and the equipment you have. For example, with carrots, you can mow or tear off the tops, then undercut with machinery, then lift. Or you can use the tops to help get the carrots out of ground, as we do, loosening them with a digging fork, then trim.

Ensure gentle treatment and no bruising of roots while harvesting. As we all know, it is important to avoid bacterial contamination. Wounds and abrasions can lead the crop to pick up new bacteria from the environment. Crops can be punctured by sharp edges of containers as well as the more obvious knives and fingernails.

The wash-pack house at Finca Marta, Artemisa, Cuba
Photo Pam Dawling

Trimming

Our method is to bring the harvested roots to a shady spot to trim, wash, sort and bag. We have a printed sheet, optimistically called “Perfect Vegetable Storage” to help us remember from year to year the tips we have learned. Usually we need scissors or knives for a clean cut, and usually we aim to leave about ¼” (0.5 cm) of leaf-stems attached to roots. It might be quicker to tear the leaves off, but this doesn’t give such good results and can cause the crop to need extra storage space. When we harvest carrots for immediate use, we snap the tops off right at the junction of the foliage and the root. When we harvest for storage, we trim with scissors to leave a small length of greens.

Washing and rinsing

After washing, and perhaps before, comes cooling. Make full use of all possibilities, such as damp burlap, or high percentage shade cloth, or the shade of trees, buildings, or a truck. At the washing station, crops may be sprayed down on a mesh table, or dunked in troughs or buckets of clean water. Washing can also act to cool the crop.

Draining away the water is important. Drain on a mesh table or in a holey bucket, a suspended mesh bag or laundry basket. Barrel root washers have the draining stage built in. We don’t have a rotary barrel root washer, much as we’d like one. Here’s our manual method.

  1. As you cut, gently drop the roots into buckets of water. This lets the dirt wash itself off to some extent, as you continue to cut more. Use whatever size and type of container seems most efficient.
  2. When the wash container is full, switch from trimming to washing: rub each root with your hands and drop it gently into a container of clean rinse water. Depending on the cleanliness of the roots after washing, it may be possible to reuse the rinse water. Or else make it be wash water for the next round. Once the water is quite dirty it needs to go. Gently pour it round a tree, or on the ground somewhere else. Avoid causing a washout by flinging a bucketful all in one place. Rinsing needs pretty clean water.
  3. When the rinse container is full, get two clean holey buckets. Take the roots one at a time out of the rinse water (don’t rub then any more, just lift them out). Sort as you go.
Harvested Purple Top Milan and White Egg turnips.
Photo Pam Dawling

Sorting storable roots from non-storable

  1. Decide if the root is Storable or is Use First (cull, or home use). Storable are sound, reasonably large. Use First may be small (less than ¾” diameter, less than 3” long, maybe) or damaged (deep holes, soft spots, fresh complex cracks). Open dry cracks or snapped-in-half roots may heal over and store just fine.
    Bucket lid with holes for sorting root vegetables for storage.
    Photo Wren Vile

    We made different sized holes in a special bucket lid, to help new people get an idea of size.

  2. Put the storable ones in one holey bucket and the non-storable (Use First) in the other. It helps to have 2 different colored buckets. It’s better to err on the side of calling doubtful ones Use First, but it’s even better to learn good sorting, as too many Use First roots can’t all be used quickly.
  3. When a Use First bucket is full, set it aside, or put on the cart or truck. Once a Storable bucket is full, set it aside to drain thoroughly before bagging. Do not confuse categories. Do more trimming, washing, rinsing, sorting.
  4. When the Storable roots have drained, get a well-perforated plastic sack. Ensure there are enough holes and big enough ones. Buy perforated bags or perforate your own. If you need more holes, the safest method is to lay the bag on the grass, stand on diagonally opposite corners, then stab the bag with a largish knife. Make about 3 cuts across the width of the bag and about 6? 7? 8? down the length. Or fold the bag and use a 3-ring paper hole punch in several places. Refold and repeat.
  5. Gently pour the Storable roots into the well-perforated bag. We usually use 50 pound bags. Tie the neck with a short length of rope and make a masking tape “flag” label with the date and the type of vegetable.
Sweet Potatoes in storage.
Photo Pam Dawling

Storing

When all the bags of storers have been gathered up, record the number going to the cooler on an Inventory clipboard. If there is no official tally sheet, make one on a full size sheet of paper.

We store bulk roots in a walk-in cooler, up on a high loft/shelf. Use pallets in the loft for better airflow under the bags. Start a new pallet for each different type of vegetable and for a substantially different date, eg fall carrots separate from spring carrots. Keep inventory: once a month, someone takes stock of what we have and updates the list.

See Root Crops in August for details on sorting newly stored potatoes

Storing potatoes

Potato crates in our root cellar.
Photo Nina Gentle

Storing potatoes

This is part of a monthly series on growing potatoes, a dietary staple.

PART ONE: Planting potatoes (April)

PART TWO: Growing potatoes (May)

PART THREE: Potato pests and diseases (June)

PART FOUR: Harvesting potatoes (July)

PART FIVE: Storing potatoes (August)

PART SIX: Planning to grow potatoes again (September)

I have a whole chapter about potatoes in my book, Sustainable Market Farming, and another on root cellars (including construction), where much of this information can be found.

This year’s new Victory Gardeners now need to learn how to store your harvest, so it can supply your household for as long a s possible. As more commercial growers aim to produce local food sustainably year-round, the storage of vegetables for sale over the winter becomes important. Understanding the needs of different crops can help reduce your electricity bill and carbon footprint, and maximize the amount of produce you can store for later sale. Only critical crops need refrigeration. Potatoes should not be refrigerated. Many others may be stored without electricity, perhaps in buildings that serve other uses at the height of the growing season.

Our in-ground root cellar. Photo McCune Porter

A 1978 publication from Washington State University Extension, Storing Vegetables and Fruits at Home, is a good introduction to alternatives to refrigerated storage, using pits, clamps and root cellars. There is also good information in USDA Agriculture Handbook 66. 2016 revision. Many growers are still using the 1986 version, but it’s worth checking newer recommendations and additional advice. UMass Extension has a good site on post-harvest and storage resources. Nancy and Mike Bubel’s book Root Cellaring has a wealth of information, including how to build a root cellar.

Don’t expect a one-shed-fits-all solution to crop storage. I identify five different sets of storage requirements, for different storage crops. This one is specific to potatoes, which don’t want colder conditions: Cool and moist: 40°F–50°F (5°C–10°C), 85%–90% humidity. With a good in-ground root cellar, potatoes can be stored for 5-8 months, but other options can also work. A max-min thermometer will help you keep the storage space in the right range.

We removed all the soil to renovate our root cellar roof. Photo McCune Porter

Reasonable expectations

Only store sound potatoes. Garbage in, garbage out. Damaged and poor quality vegetables will not store well. Always handle all crops for long-term storage gently, to avoid bruising. For long-term storage, make sure crops are fully mature but not over-mature when you harvest. Potatoes need firm skins that don’t rub off when you rub with a thumb. This is different from some crops, such as beets and sweet potatoes, that don’t have a “ripe” stage, but are ready when they reach the size you like. Very small vegetables don’t store well. Expect that a small percentage of your crops will go bad in storage — it’s not a sign of failure, just a reminder that life has limitations.

Cure, then store

Potatoes are one of those vegetables that need to cure before storage in conditions that are different from those needed for storage. Curing allows skins to harden and some of the starches to convert to sugars. See the post on Harvesting Potatoes in July. Potatoes need curing in moist air (90% humidity) for one to two weeks at 60°F–75°F (15°C–24°C). You may be surprised at how warm this is. Wounds in the skin will not heal below 50°F (10°C).

We sort our potatoes after two weeks of curing and find this usually reduces the chance of rot so that we don’t need to sort again. With potatoes, the rate of deterioration drops right down after a few weeks. Remember to keep white potatoes in the dark while curing as well as during storage.

When filling stackable crates, leave space for the crates to lock into each other.
Photo Nina Gentle

Preparation for storage

Plan your storage sites, buy a thermometer for each site, and gather suitable containers. Clean and prepare your storage space before going out to do a big harvest. Wood crates are good for nostalgia and agritourism, but plastic is kinder on aging backs and less likely to harbor diseases. Containers should rest on shelves, pallets or blocks of some kind, and not be set on bare concrete floors. This helps improve ventilation and reduce condensation.

For traditional storage without refrigeration, potatoes (and most other root crops) store best unwashed (less wrinkling), though this can make them harder to clean later. If you might not be able to keep temperatures low enough, choose stackable crates rather than closed bags. When you have choice in the matter, try to harvest potatoes from relatively dry soil, so they are less likely to grow mold. The packing of your containers should allow for airflow, but you don’t want the produce to shrivel up, so be observant. Sometimes night ventilation offers cooler, drier air than you can get in the daytime. Keeping root cellar temperatures within a narrow range takes human intervention, or sophisticated thermostats and vents. If needed, electric fans can be used to force air through a building.

Ethylene

Ethylene is an odorless, colorless gas, generally associated with ripening, sprouting and rotting. Chilling, wounding and pathogen attack can all induce ethylene formation in damaged crops.

Some crops, including most cut greens, are not very sensitive to ethylene and so can be stored in the same space as ethylene-producing crops. Potatoes are very sensitive to ethylene and will sprout in a high-ethylene environment.

Some crops, such as ripening fruits, produce ethylene gas while in storage. Don’t be tempted to set that bargain box of very ripe bananas you bought on the way home near anything you don’t want to sprout or ripen further. Propane heaters and combustion engines produce ethylene. Be careful if using your garage to store potatoes.

Our 10’ x 11.5’ (3 x 3.5 m) cellar will hold 10,800 pounds (4900 kg), or around 5 tons (tonnes)of potatoes. Photo Pam Dawling

Basement storage rooms and root cellars

Traditional root cellars are made by excavating a large hole near the house, lining it with block or stone-work walls, casting a well-supported and well-insulated concrete roof, then covering the top with a big mound of soil. The doorway may have bulkhead doors or an entry way with additional doors. The more modern version is to construct an insulated cellar in the basement of a building such as a CSA distribution barn or your house. See the Bubels’ book, or the Washington State publication for drawings and instructions on making these. Provide wide doorways with ground-level access if possible (roll that garden cart right in!). Good lighting and drainage are important, so you can see if everything is storing well, or hose the shelves and floor down if it isn’t. Mouse-proofing is worth considering upfront. Our 10’ x 11.5’ (3 x 3.5 m) cellar will hold 360 crates with an ample central path. That’s 10,800 pounds (4900 kg), or around 5 tons (tonnes).

Black snakes control mice in the root cellar. Photo by Nina Gentle

 Root Cellar Ecosystem

Store potatoes in a moist, completely dark cellar, ideally at 40°F (5°C), up to 50°F (10°C). Ventilate as needed during times of cool temperatures, to maintain the cellar in the ideal range. We need to actively manage conditions in our root cellar to cure the potatoes and help them store well. We have no automated ventilation, or even ventilation ducts. We simply leave the door open at night when we want to cool it down, or in the daytime in winter. We just choose a time when the forecast temperature is in the range we’re aiming for. Yes, mice do come in the open door! We encourage black snakes to live in our cellar, to keep the mice under control. (How do we encourage snakes? I mean we don’t drive them out, and if we need to, we move one or two in there.) This can be a bit unnerving, as the cellar is dark. (We chose not to have a light, as leaving it on by accident could cause a lot of potato greening before we noticed our mistake.) We have developed a special door-opening technique so we can co-exist with the snakes, who like to hang out on the top of the doorframe. We unlatch the door, open it a crack, then bang it closed, before opening it fully. Any resting snakes have by then dropped to the floor where we can see them and avoid them. (No snakes have been hurt in this process!) People who don’t like snakes will be really motivated to fit a rodent-proof vent system!

I wrote a blog post about Root cellar potato storage, on 8/07/2018. It includes a fuller version of our Root Cellar Warden instructions below. Here is the shorter, post-harvest version of our “Root Cellar Warden” instructions:

  • After the potato harvest, the potatoes need to be at 60-75F (15-24C) with good ventilation for two weeks. Leave the door open on mild nights (or days) every 2 or 3 days, and close it later. The newly harvested potato is still respiring and needs fresh air. Lack of sufficient oxygen during curing results in Black Heart, a condition where the tubers develop nasty black lumps of dead tissue in the centers, so be sure to provide good ventilation during curing.
  • After 14 days, the potatoes need sorting to remove Use First and Compost ones. Usually this is done by bringing the crates outdoors. You will need buckets, rags, gloves. It’s important to do this in the 3rd week after harvest, and not leave it longer, to minimize the spread of rot. Keep the crates away from walls, which sometimes collect condensation. The potatoes benefit from the airflow if they are not touching the walls.
  • After 14 days, cool the cellar whenever a mild night or chilly day is forecast, down to 40-45F (4.5-7C).
Sorting potatoes two weeks after harvest.
Photo Wren Vile

Dormancy Requirements of Potatoes

We researched the dormancy requirements of potatoes in an effort to store ours so they don’t sprout when we don’t want them to.

What I know so far about dormancy is that potatoes need a dormancy period of 4-8 weeks after harvest before they will sprout. So if you plan to dig up an early crop and immediately replant some of the potatoes for a later crop, take this into account. Get around this problem by refrigerating them for 16 days, then chitting them in the light for 2 weeks. The company of apples, bananas or onions will help them sprout by emitting ethylene.

To avoid sprouting, keep the potatoes below 50F (10C) once they are more than a month from harvest, avoid excess moisture, and avoid “physiological aging” of the potatoes, caused by stressing them with fluctuating temperatures, among other things. If eating potatoes do start to develop sprouts, it’s a good idea to rub off the sprouts as soon as possible, because the sprouting process affects the flavor, making them sweet in the same way that low temperatures do.

I have also written blog posts about

Potato Research on Harvest and Storage,

What Makes Potatoes Sprout,

How to Deal with Green Potatoes (one of my most-read blog posts!)

and if you still want to read more about potatoes,

Book Review “Potato: a history of the propitious esculent” John Reader, Yale University Press 2008

Read a whole book about the potato. Abe Books, John Reader

Organic and Alternative Methods for Potato Sprout Control in Storage

Mary Jo Frazier and colleagues at the University of Idaho Extension, in 2004, researched the use of essential oils of mint and cloves to inhibit sprouting in storage. These plant oils can add 20-30 days storage, and then need to be reapplied. There is the issue of flavors carrying over into the tubers.

Other biocontrols to reduce storage losses

There has been some USDA ARS (Agricultural Research Service) research into biological disease control for stored fruit and vegetables. It takes three directions:

  • Using biologicals such as Aspire yeast, Bio-Save Bacteria (Pseudomonas syringae) or chitins to form a semi-permeable film over the surface of the roots and fruits;
  • UV light to induce rot resistance. Primarily used for fruit;
  • Natural fungicides derived from jasmine and peaches, which induce disease resistance in the crop itself.

Currently these methods are only used by large operations, but in the future, they may be useful to small growers.

Potato harvest.
Photo Nina Gentle

Root Crops in August

Root Crops in August

Misato Rose Winter Radish.
Photo Southern Exposure Seed Exchange
China Rose Winter Radish.   Monticello Shop

Root Crops to Plant in Central Virginia in August

Like July, August is not a good month for sowing many root crops in Virginia – it’s very hot. However, the daylight is getting shorter and so the hot part of the day is also getting shorter.  And the calendar is boxing us in. The month of August is when we establish crops that will feed us in the fall and winter.

Carrots:

On August 4, we sow our fall carrots, enough to store and feed us all winter. Twin Oaks can eat 30+ bags (50 lbs, 23 kg each) of carrots during the winter, so we try hard to grow a big crop of fall carrots. See Root Crops in May for more about sowing and growing carrots, including pre-emergence flame weeding.

Good irrigation is important for successful carrot growing in hot weather.
Photo Bridget Aleshire

Carrots do very poorly with competition, so try to grow them in a bed that had only light weeds. You can use the Stale Seedbed Technique, where the bed is prepared ahead of time, and one or more flushes of weeds are germinated and flamed or hoed off. Carrots do well on raised beds, because the soil stays loose and the roots can easily grow deep.

Some people bake old carrot seed to dilute the good new seed, to reduce the thinning work and the wasted seeds. Some people sow in single rows 8-10” (20-25cm) apart. Others sow in bands 2″ (5 cm) wide, at 8” (20cm) apart, with one length of drip-tape serving two bands in one 16-24″ (40-60 cm) bed.

Hard rain in the first 3 or 4 days after planting can dry to a crust that could prevent emergence. If you get heavy rain, irrigate for half an hour each day afterwards until the carrots emerge. Some people use shade cloth to help keep the soil surface moist.

We flame summer carrots on day 4 after sowing, because we have found that carrots can emerge on day 5 in summer temperatures, despite longer times given in the charts. The idea is to flame the beds the day before the carrots are due to emerge.

Table of days to germination of beets and carrots at various temperatures

Days to Germinate 50°F (10°C) 59°F (15°C) 68°F (20°C) 77°F (25°C) 86°F (30°C) 95°F (35°C)
Carrots 17.3 10.1 6.9 6.2 6.0 8.6
Beets 16.7 9.7 6.2 5.0 4.5 4.6

If we are unable to get our fall carrot sowing finished in early August, we sow them in late August. We try to avoid sowing in the middle of August when the hordes of baby grasshoppers emerge. If we have to sow in the middle of August, we use hoops and fine mesh ProtekNet, battened down well around the edges to keep the pests out. The hoops hold the netting up above the foliage, keeping it inaccessible to insects.

Beets

Beets can be tricky to germinate in hot weather, but to get a good storable-sized root, we need to get them established by 8/20 at the latest. (Our first frost date is 10/15 to give you an idea of when things cool down.) We get ready to sow on 8/1, but sometimes we wait for a cooler spell. I like the Cylindra beet. The shape is long (good for slicing), the skins come off easily, and the flavor is very sweet and the texture tender.

Young Cylindra beets.
Photo Wren Vile

We direct sow either dry beet seed, or some we have presoaked for 1-2 hours. Beet seed drowns easily: don’t use too much water or soak for too long.  Either way, sow 1/2″-1″ (1-2.5 cm) deep, tamp the soil firmly so that the seed is in good contact with the soil and its life-saving water supply. Keep the row damp, by watering daily as needed for the 4-6 days they take to emerge. Beets prefer 50°F–85°F (10°C–29°C). Some people lay boards over the seeded rows but then you have to be sure to check frequently and remove the boards when the seedlings emerge. Other options include covering the beds with shadecloth on hoops, or making some other temporary screen to the south side.

Turnips:

I mentioned turnips in July as a crop to harvest. That was the spring-sown turnips. We sow our fall turnips 8/15 or up until 9/15 (our absolute latest). Turnips can be up the next day, even at 95°F (35°C). Most will be Purple Top White Globe for winter storage. Because of the high populations of harlequin bugs, and sometimes aphids or flea beetles, and cabbage caterpillars, we hoop and net all our fall brassicas. We like ProtekNet (for smaller amounts than a whole roll, try Johnnys)

Brassica transplants under ProtekNet. (I couldn’t find a photo with turnips) Photo Bridget Aleshire

Winter radish:

In central Virginia, we sow winter radish on August 4. They have no trouble germinating at high temperatures. We like to grow Misato Rose, Miyashige Daikon and Shunkyo Semi-Long.

China Rose winter radish.
Photo Southern Exposure Seed Exchange

Kohlrabi:

Early Purple Vienna and Early White Vienna can still be sown here in August. They take only 60 days from sowing to harvest. They can be direct sown or transplanted from flats or an outdoor nursery seedbed. Kohlrabi is hardy to maybe 15°F (-9.4°C). It doesn’t get that cold here before the beginning of November, so counting back 31 days in October, plus 30 in September, plus 31 in August – that’s 92 days already, more than enough. We can sow kohlrabi in early August and get a crop at the end of October.

Purple kohlrabi
Photo Small Farm Central

For fall brassica crops, we use an outdoor nursery seedbed and bare root transplants, because this fits best with our facilities and our style. Having the seedlings directly in the soil “drought-proofs” them to some extent; they can form deep roots and don’t dry out so fast. Other people might prefer to sow in flats.

We cover the beds with ProtekNet insect mesh on wire hoops until the plants are big enough to stand up for themselves against “pest bullying”. Overly thick rowcover or rowcover resting directly on the plants can make the seedlings more likely to die of fungal diseases in hot weather – good airflow is vital.

We aim to transplant most brassicas at four true leaves (3-4 weeks after sowing). In hot weather, use younger transplants than you would in spring, because larger plants can wilt from high transpiration losses. If we find ourselves transplanting older plants, we remove a couple of the older leaves to reduce these losses.

Fall radishes:

Easter Egg radish seedlings in early September.
Photo Pam Dawling

We direct sow small radishes from mid-August (best) to mid-September (latest). Our favorite is Easter Egg, a mix with a range of colors that don’t all mature on the same day, but feed us over a couple of weeks. They are less likely to get fibrous than Cherry Belle or Sparkler types.

Root Crops to Harvest in Central Virginia in August

Carrots:

I usually reckon on three months from sowing to harvest for carrots, but they can be faster in warm weather. See Root Crops in June for more on carrots. If you sowed carrots in May, they should be ready to harvest in August. Don’t delay or they will become woody in texture and soapy in flavor. I suppose they are still nutritious, so if this has happened to you, blend into soups or make flavorful stews.

Turnip thinnings:

A few weeks after sowing, you will need to thin your turnips. You can use the tiny thinnings as microgreens for salad, and the bigger ones (with marble-sized turnips attached) can be gently steamed or braised.

Potatoes being harvested.
Credit Kathryn Simmons

Potatoes:

Depending when you planted your potatoes, they could be ready from mid-June onwards. They take about 4 months to reach maturity, so during August, potatoes planted in April will become ready.

See Potato Harvesting and Root Crops in June for more on harvesting. For best storability, wait until two weeks after tops have died to harvest. During that time, the skins will toughen up and you’ll have fewer harvest injuries. Potatoes can bruise! They may look tough and inert, but they are living plant matter and should not be thrown or banged about. To test if potatoes are ready to store, dig up two potatoes and rub them together, or rub them firmly with your thumb. If the skins rub off, wait a couple of days before trying again. If the skins are strong, go ahead and harvest. see next weekk’s post for more on storing potatoes.

Other Root Crop Tasks in Central Virginia in August: sorting potatoes, thinning carrots and turnips

Sort potatoes

Sort potatoes two weeks after storing. Transfer the potatoes individually into clean crates, checking them for any dampness or softness. We triage (sort into three categories); those good to continue in storage, those fit only for the compost bin and anything we’re not sure about, but hope is not a total loss. We take these optimistically to our kitchen and plan to use them soon, if necessary cutting away bad portions. We find that this single sorting two weeks after putting the potatoes into storage can make all the difference. Most potatoes have “declared themselves” as fit or not by this point. Removing the rotting ones prevents the rot spreading. Often this is the only sorting we do. If you have time (or no bags of pasta in the pantry), you could aim to sort once a month until deep in the winter.

Sorting potatoes two weeks after harvest, to remove problems.
Photo Wren Vile

Ventilate the root cellar every few nights when it is coolest. Gradually get temperature down to 65°F (18°C). Try not to have temperature reversals. You don’t want to chill the potatoes yet – they are still breathing and need time to settle into dormancy.

Next week’s post will be devoted to storing potatoes successfully. It will be Part 5 of my Potatoes series. If you’re reading this in the southern hemisphere, you can use the Search box to find information of planting potatoes. Just add or subtract six months from my accounts.

Carrot thinning:

It is much easier to see the carrots, and they grow better if the first flush of weeds has been flamed off. Get to the initial thinning of carrots as soon as you can, spacing to about 1” (2.5 cm) apart, weeding at the same time. We usually have someone with good eyesight and hand-eye co-ordination hoe between the rows the day before the hand-weeding. If you are in an area with Carrot Rust Fly (Carrot Root Fly), remove all thinnings and broken foliage from the field, so you don’t lure the low-flying pest with the wonderful smell of the broken leaves. We do a second thinning, to 3” (8cm) at the stage when the baby carrots can be used for salads. If we get more weeds, we might do another round of weeding before harvesting the full size carrots. If carrots are spaced too widely, they will be more likely to split, and the overall yield will be reduced.

Carrot row thinned to one inch.
Photo Kathryn Simmons

Mowing:

Keep edges mowed, and any buckwheat cover crop not seeding, so that you don’t encourage grasshoppers.

Special Root Crop Topic for August in Central Virginia: Sowing and transplanting when soils are hot.

There are definitely some challenges to getting seeds germinated in hot weather. And a different set of challenges to transplanting (not so applicable to root crops, as most are direct-seeded.)

 Here are some tips to try:

  • Choose suitable varieties. Read the catalog descriptions carefully. Look for flavor, productivity, disease resistance and cold-hardiness as well as heat-resistance. The crops you sow now need to emerge in hot weather and keep growing into cold weather.
  • Consider direct-seeding crops rather than transplanting them. They can be more cold-tolerant, probably because there’s no damage to the taproot. And transplants can struggle to recover from transplanting when it’s very hot.
  • Good soil preparation is important. Avoid over-cultivating before planting, as this makes crusting more likely.
  • Water a day ahead of sowing or transplanting, to reduce the need to water copiously afterwards. Pre-water furrows for large-seeded crops (I can’t think of any root crops with large seeds, off the top of my head).
  • Plant seeds deeper than you would in spring, as the soil is already warm and you want to guard against the seeds drying out. In cold weather we are guarding against seed rotting in cold wet soil.
  • You could sprinkle sand, grass clippings, straw or sawdust lightly along the rows.
  • After sowing, watering should be shallow and frequent, using fresh-drawn cold water, not something from a hose in the sunshine. For close-planted small seeded crops, use overhead sprinklers. Chilled water, night watering, and even ice on top of the rows can help reduce soil temperatures as well as supplying vital moisture.
If using a nursery seed bed, you can put ice cubes on top of rows of seeds in hot weather to help cool the soil.
Photo Bell Oaks

Sowing when soils are hot

Check the germination requirements for your crop (see Sustainable Market Farming), and the expected number of days to emergence under your field conditions, and use a soil thermometer.

If the soil temperature is too high for good germination, cool a small part of the outdoors. You could use the shade from other plants, shadecloth, boards, or damp burlap bags. For crops you normally direct seed, consider cooling a small nursery bed for your seedlings and transplanting later.

If outdoors is too challengingly hot, start your seeds indoors. Put a sown flat in a plastic bag in your refrigerator or in a cool room. Try the basement floor, perhaps. Cover flats with wet newspapers until the seedlings emerge. You could use plug flats or soil blocks rather than open flats, to reduce transplant shock.

Soaking seeds – a help when temperatures are high and soils are dry.

The length of time to soak a seed depends on its size: bigger seeds can benefit from a longer soak. Soak large seeds like beans and peas overnight before planting. It helps them get all the water they need to absorb for the initial sprouting. After that the smaller amounts needed to emerge are more easily found. Don’t soak legumes so long that the seed coat splits, or they lose nutrients and may get attacked by fungi.

Smaller seeds may only need to soak for 1-2 hours. I suspect that when I’ve had failures with soaked beet seeds, I soaked them for too long and they suffocated from a shortage of oxygen. Small seeds that have been soaked tend to clump together, so after draining off as much water as possible, mix them with a dry material like uncooked corn grits, oatmeal or bran, or use coffee grounds or sand to make them easier to sow thinly.

If you are using a seeder, spread your soaked or sprouted seeds out in a tray for a while to dry the surfaces. Experiment on a small scale ahead of a big planting, to make sure your seeder doesn’t just grind the seeds up, or snap off any little sprouts.

Pre-sprouting seeds to plant

To pre-sprout seeds, first soak them in a jar, then drain off the remaining water and put them in a cool place. Rinse twice a day, draining off the water. Sprout the seed just until you see it has germinated. For most crops 0.2″ (5 mm) is enough. Seeds with long sprouts are hard to plant without snapping off the shoot. If your pre-sprouting has got ahead of the weather or the soil conditions, slow down growth by putting the seed in the refrigerator. If you have leftover soaked or pre-sprouted seeds, you can store them in the fridge while the others come up, and then use them to fill gaps.