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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Cooking Greens in October

 

Vates kale in the fall.
Photo Bridget Aleshire

Cooking Greens to Harvest in Central Virginia in October

Beet greens, broccoli, cauliflower, cabbage, chard, Chinese cabbage, collards, kale,  komatsuna, Maruba Santoh, pak choy, senposai, spinach, tatsoi, Tokyo Bekana turnip greens and Yukina savoy can be available here all month (and perhaps longer, depending on the temperature). OP Yukina Savoy seems more cold-hardy  and bolt-resistant than the hybrid Koji.

The new outdoor greens this month are tatsoi, kale, spinach, collards, and mizuna (if we have that outdoors).

Eat-All Greens harvests can start, if you sowed some last month. When we sowed some on September 16, we got two harvests in October and several in November.

From the hoophouse we start to harvest spinach, tatsoi, and leaves of Tokyo bekana.

Cooking Greens to Sow in Central Virginia in October

This month we finish sowing spinach and kale for overwintering outdoors (10/30 is our last chance). No more outdoor sowings until spring!

“Filler Greens”

Filler greens: short rows of Tokyo bekana, Yukina Savoy and senposai used to fill gaps in the winter hoophouse.
Photo Pam Dawling

On October 10, we sow Brassica fillers #1. These are short rows of senposai, Tokyo bekana, Yukina Savoy, Maruba Santoh,  to use to fill gaps later during the winter as soon as they occur. We simply dig them up, replant where needed and water well. Alternatively you could keep some plug flats of these plants handy. Bare-root transplanting is much easier than many fear.

During December we use the “Filler” greens plants to replace casualties and harvested heads of Tokyo bekana, Maruba Santoh, Chinese cabbage, Pak choy, Yukina Savoy and tatsoi daily. We stop filling gaps in these early harvest crops on December 25, as they will bolt in the hoophouse conditions in January at the latest.

We continue to fill gaps elsewhere with senposai until January 25. Asian greens don’t make good growth before bolting if transplanted after January 25. From January 25 to February 20 we fill all gaps everywhere with spinach transplants

Hoophouse Bed preparation and Planting

In the hoophouse we have a lot of bed preparation (all the beds except the Early Bed which we plant in September), as well as transplanting and sowing.

On October 14, we sow turnips #1: Red Round (1 row on North), Hakurei (2 rows South). Oasis, White Egg.

On October 20, we sow Filler Greens #2.

By October 23, we clear and prepare two more beds and sow spinach #2; tatsoi #2, turnips #2, chard #2 and perhaps Frills (Frilly Mustards) #1.5.

Brassica (Mustard) Salad Mix

Interesting mustard mixes are sold for salad mixes. We often mix our own Brassica Salad Mix from leftover random brassica seeds. For a single cut, almost all brassicas are suitable – just avoid turnips and radishes with prickly leaves! We sow between October 2 and November 14 for harvests during the winter, and from December 4 to February 12 for March and early April harvests.

We could, but so far we haven’t, sow Eat-All Greens in hoophouse in October.

Catch crops

Useful if a crop fails, or you have an empty space. Don’t delay, as rates of growth slow down as the temperatures and daylight decrease. Don’t expect much from sowings during the Persephone Days (less than 10 hours daylight).

Tokyo bekana is a quick-growing Asian green, for cooking or salads.
Photo Twin oaks Community

This year we grew an early catch crop of Tokyo bekana when we realized we had space that wouldn’t be needed till mid-October (for turnips). We direct sowed it August 28, weeded and thinned to 1” (2.5 cm) on September 5; weeded and thinned to 3” (7.5 cm) on September 16, using the small plants for salad. We need to clear this crop by the middle of October to sow the turnips, and the Tokyo bekana has got to a fine size.

  • Ready in 30–35 days in fall, longer in winter: brassica salad mixes, spinach, chard, salad greens (lettuce, endives, chicories), winter purslane., kale, arugula, radishes (the fast small ones and the larger winter ones), many Asian greens: Komatsuna, Maruba Santoh, mizuna, frilly mustards, Senposai, tatsoi, Tokyo Bekana and Yukina Savoy.
  • Ready in 35–45 days in fall: corn salad, land cress, sorrel, parsley and chervil.
  • Ready in 60 days in fall: beets, collards, kohlrabi, turnips

Cooking Greens to Transplant in Central Virginia in October

September sown White Russian kale (transplanted in October).
Photo Wren Vile

In our hoophouse in early October, we transplant Tokyo Bekana, Chinese cabbage, Pak choy, Yukina savoy #1,  using plants which we sowed outside under insect netting.

By October 13, we transplant chard #1, Frills #1, and Red and White Russian kales, from our outdoor nursery seedbed.

By October 21, we clear and prepare another bed and transplant 1/2 bed kale, plus Yukina Savoy, and frilly mustards. (This is our favorite crop selection to suppress nematodes),

By October 23, we clear and prepare two more beds and transplant senposai and Yukina Savoy #2 from the outdoor nursery bed.

Other Cooking Greens Tasks in Central Virginia in October

October is our month to weed and thin the fall crops in the outdoor raised beds, especially spinach and kale. We thin kale to 12” (30 cm); perhaps more space would be better, although Vates is a dwarf variety.

We put rowcover over any beds of pak choy, Chinese cabbage or Tokyo bekana we have that year. Later we weed (again!) and cover the spinach for faster growth, but leave the kale uncovered after a bad experience of Vates kale with rowcover fibers mixed in. The cooks didn’t love us!

Galinsoga dies with the frost.
Photo Wren Vile

We prefer to wait to cover spinach after frosts kill the galinsoga. As well as raised beds, we plant spinach in our cold frames, making good use of the space until the frames are needed in spring for hardening off transplants.

We roll, label and store drip tape from the fall broccoli and cabbage

Special Cooking Greens Topic for October: Get Soil Tests; Be Ready for Cold Nights.

October is a good month to do soil tests, when the soil is not too wet, and the soil temperatures are still warm (the soil life is active).

Weather Forecasting

We use Wunderground, but subtract 5F° from their forecast night lows for our nearest town, and mentally downgrade the chance of rain by 10%, as rain often passes us by as it scoots along the river valley north of us.

See Weatherspark.com for the typical ranges of weather in your area:

Savoy cabbage with frost.
Photo Lori Katz

Predicting Frost

Frost is more likely at Twin Oaks if:

  • The date is after 10/14 or before 4/30 (our average first and last frost dates).
  • The Wunderground forecast low for Louisa Northside is 37°F (3°C) or less.
  • The daytime high temperature was less than 70°F (21°C).
  • The temperature at sunset is less than 50°F (10°C).
  • The sky is clear.
  • The soil is dry and cool.
  • The moon is full or new (maybe to do with tides and gravity?).
  • If temperatures are falling fast, the wind is from NW and the sky is clear, then polar air may be moving in, and we’ll get a hard freeze.
  • The dew point forecast is low, close to freezing. Frost is unlikely if the dew point is 43°F or more.

Watch for cold night temperatures and decide which crops to harvest, which to cover, which to abandon:

In a double-layer hoophouse (8F/5C warmer than outside) plants can survive 14F/8C colder than outside, without extra rowcover; with thick rowcover (1.25 ozTypar/Xavan) plants can survive at least 21F/12C colder than outside.

The hoophouse winter crops are an important part of feeding ourselves year-round

Each winter I update my Winter-kill Temperatures of Cold-Hardy Vegetables.

Here are some early winter numbers for killing temperatures outdoors (without rowcover unless otherwise stated). Your results may vary!  Let me know!        

35°F (2°C): Basil.

32°F (0°C): Beans, cucumbers, eggplant, melons, okra, peppers, tomatoes.

27°F (–3°C): Many cabbage, Sugarloaf chicory.

25°F (–4°C): Some cabbage, chervil, chicory roots for chicons and hearts, Chinese Napa cabbage, dill, endive, some fava beans, annual fennel, some Asian greens (Maruba Santoh, mizuna, most pak choy, Tokyo Bekana), some onion scallions (many varieties are hardier), radicchio.

22°F (–6°C): Some arugula (some varieties are hardier), Bright Lights chard, large leaves of lettuce (protected hearts and small plants will survive colder temperatures), rhubarb stems.

20°F (–7°C): Some beets, broccoli heads (some may be OK to 15°F/-9°C), Brussels sprouts, some cabbages (the insides may still be good even if the outer leaves are damaged), celeriac, celtuce (stem lettuce), some head lettuce, some mustards/Asian greens, flat leaf parsley (curly parsley is hardier), radishes, most turnips.

15°F (–9.5°C): Some beets, beet greens, some broccoli, some cabbage, rowcovered celery, red chard (green chard is hardy to 12°F (-11°C)), cilantro, endive, some fava beans, Russian kales, kohlrabi, some lettuce, especially medium-sized plants with 4-10 leaves, curly parsley, rutabagas if not covered, broad leaf sorrel, turnip leaves, most covered turnips, winter cress.

Frosted daikon radish.
Photo Bridget Aleshire

Twin Oaks October Calendar (Slowing Down)

Morris Heading Collards – our favorite
Photo credit Kathryn Simmons

Here’s our list of tasks for October. If you garden in zone 6 or 7, your list might be similar. If you live in a very different climate zone, leave a comment about your list for October, and how many weeks different your area is from ours.

During the month

Weed and thin fall crops in raised beds, especially spinach and kale. Thin carrots to 3”, kale to 12”.

Lettuce Factory: Transplant sowing #37 to fill cold frames; #38, 39, 40, 41, 42 in Greenhouse beds (9″ spacing).

Frost Alert:

Watch the forecast and if frost is expected that night

When frost threatens, harvest all peppers exposed to the sky. Corona is one of our favorite orange peppers. Photo credit Kathryn Simmons

Harvest peppers facing the sky, tomatoes, cauliflowers, corn, cowpeas, limas, eggplant, melons, cukes, okra, winter squash, Blues cabbage (hardy to 25°F), if not already done.

Double hoop and cover: lettuce, celery (hardy to 16°F with row cover).

Spring hoop and cover: squash, cucumbers.

Cover celery to extend the harvest into mid-winter. We like Ventura.
Photo credit Kathryn Simmons

Rowcover (no hoops): beans, Chinese cabbage, pak choy, Tokyo bekana, seedlings for hoophouse, collards  (hardy to 10°F, but cover keeps quality).

Cold frames:  Row cover between 32-28°F.  Add lids between 28-15°F.  Add quilts below 15°F.

Foliar spray greens with seaweed a few days before frost, to toughen them up.

Use overhead irrigation on peppers & tomatoes at night and some raised beds with tender crops.

Early Oct: Finish sowing spinach, kale by 7th for overwintering (last chance).

Transplant lettuce #37 to fill cold frames; #38, 39 in Greenhouse (9″ spacing).

Roll up drip tape from winter squash and sweet potatoes.

It’s time to roll up the drip tape from the watermelon, winter squash and sweet potato patches, in preparation for disking and sowing winter cover crops.
Photo credit Kathryn Simmons

Move stored garlic from basement to fridge – store below 40°F or above 56°F, never 40-50°F.

Mid Oct: Till finished raised beds and sow wheat or rye before the end of the month.

Garlic Beds: Compost (5-6 tractor buckets), till and prepare beds.

Transplant lettuce #40, 41, 42, 43 in Greenhouse as needed, filling any gaps.

Get soil tests done, when soil is not too wet.

5th fall disking: By mid-month disk and sow cover crops where possible. Sow wheat or rye as covercrops – too late for oats or most clovers (Austrian Winter Peas Sept 15-Oct 24).  Could sow winter wheat mid-Sept to early Nov (good for small plots that are hard to reach with the tractor) and after sweet potatoes).

Harvest peanuts mid-late Oct after a light frost.  Wash, dry, cure 6 days in solar dryer facing east (don’t heat over 85°F), store.

A well-covered sweet potato patch.
Photo credit Kathryn Simmons

Harvest sweet potatoes before soil temps go much below 55°F, or night air goes below 50°F: on 3 mild days – generally in the week that first frost usually occurs (10/7-14). Even a few hours exposed to temps below 50°F will cause chilling injury. (Frost on the leaves does not of itself damage the roots). Clip vines, dig carefully, set tubers in plant-clusters to dry on the soil. Select seed tubers (med-size tubers from high-yielding plants).  Save 100 Georgia Jet, 100 Beauregard, 20 each White and Jubilee. Cure in boxes with wood spacers and cover with newspaper, in basement with furnace going full time, for 7-10 days (85-90°F, 80-90% humidity).  Use fans. Splash water on floor. Curing is complete when skin is undamaged after rubbing two together. Restack boxes in storage cage.

Harvest white potatoes before the first frost (average Oct 14) if possible. Cure in root cellar at 60-75°F for 2 weeks, with good ventilation, then cool the cellar to lower temperatures: 50°F by 10/31, then 40°F for the winter.

Late Oct: Transplant lettuce #44, 45, 46 as filler in Greenhouse. Double hoop and cover spinach.

Planning: List successes & failures from labels. Prepare Garden Planning Schedule, Crop Review Sheets. Clean labels after info is recorded. Pray for a killing frost. File crop record info. Audit labor budget and plan endgame. Plan main garden layout. Hold Crop Review meeting.

Clear winter squash, tomatoes and peppers in order to sow cover crops, by 10/24 if possible. Sow rye alone or with crimson clover or winter peas. Crimson clover by 10/14; AWP, wheat by 11/8

6th fall disking: After the killing frost, or end of Oct if no frost: pull up tomato stakes and roll up drip tape, disk nightshades, melons, winter squash, sweet potato and white potato patches.

Check through veg in storage, squash once a week, white potatoes two weeks after harvest.

Perennials:Last mowing of clover in grapes in early Oct, not too short, and not too late in the year. Weed & mulch strawberry beds, and remove extra runners. Renovate if not already done. Start weeding, fertilizing and mulching the blueberries, raspberries, rhubarb and grapes.

Time to say goodbye to the rhubarb until April.
Photo credit Kathryn Simmons

October Harvests: Asparagus beans, beans, beets and beet greens, broccoli, cabbage, cantaloupes, carrots, cauliflower, celeriac, celery, chard, Chinese cabbage, collards, corn, cow peas, cukes, edamame, eggplant, horseradish, hot peppers, kohlrabi, komatsuna, leeks, lettuce, limas, maruba santoh, okra, pak choy, peppers, radishes, Roma paste tomatoes, scallions, senposai, spinach, tatsoi, tokyo bekana, tomatoes, turnips and turnip greens, winter radishes, winter squash, yukina savoy, zucchini.  Could lightly harvest rhubarb before frost.