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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Farming Conference Tips, Hoophouse Cool Season Crops slideshow.

I’ve just been on an intensive conference hopping jaunt, three weekends in a row with not much time at home mid-week. One notion I heard discussed is the “Actionable Nugget”. It’s an idea you learn from someone else that inspires you as a possible solution to a problem or challenge you’ve noticed. I’m going to share some I picked up this month.

First I’m going to share my half-day presentation on Hoophouse Production of Cool Season Crops. To view it full screen, click on the diagonal arrows icon. Use the forward pointing triangle to move to the next slide. There are a lot! It was a full afternoon!

Here are some of the Actionable Nuggets:

Asparagus Beans (Asian Long Beans, Yard-Long Beans) as a summer hoophouse crop.

Purple-podded asparagus bean.
Photo Southern Exposure Seed Exchange

I got this idea from a Year-Round Organic Vegetable Production workshop at the Virginia Association of Biological Farmers Conference. It was presented by Rick Felker of Mattawoman Creek Farms on the Eastern Shore of Virginia. Rick said that Asian long beans are a star crop for them, and  produce extremely high yields compared to outdoors. Yes, they need trellising, and yes, they need frequent harvesting.  On the plus side they are a legume, so they are adding nitrogen to the soil the whole time they are growing. At Mattawoman Farm, they harvest these from June to October.  In recent years we have not been growing bean seed crops in the summer hoophouse as we used to do. Last summer we grew Iron and Clay cowpeas as a cover crop, but were disappointed to need to cut them back every 6 days, because we’d decided not to stake them in any way.

Trellised Liana asparagus bean.
Photo Southern Exposure Seed Exchange

Sulfur: The Forgotten Nutrient, Secret Ingredient for Healthy Soils and Crops.

At the Future Harvest Chesapeake Association for Sustainable Agriculture Conference, I much appreciated this workshop by Ray Weil. A whole workshop on one element! When deficient, the plant has symptoms resembling nitrogen shortage. It caused me to wonder how often I have made this mistake. Brassicas and legumes are the crops to pay closest attention to. I learned that the standard soil test for sulfur is fairly meaningless – I have been putting my faith in a poor source of information. The key piece of information from Ray Weil is that with a S shortage, the yellowing starts on the younger leaves, which is opposite to nitrogen shortages, when the yellowing begins on the older leaves.

S-deficient plants will be thin, spindly and slow-growing. The leaves will be high in nitrates, because the poor plant can’t use all the N it has absorbed from the soil. I already know from winter hoophouse growing that high levels of nitrate are not healthy. Legumes cannot do a good job of fixing nitrogen if S is too low. Sulfur shortages can affect the nutrient density of the crops, the protein level in beans. Now I know what to look for and what to do if I find the problem. Add 5-10 pounds per acre of S if plants seem deficient.

Cucurbit Blossom End Rot

Is this an unpollinated squash or one with Blossom End Rot?
Photo Pam Dawling

At the same FHCASA conference, I learned about cucurbit BER in a workshop by Emily Zobel. I had not known cucurbits could suffer from blossom end rot, which is a problem caused by limited calcium uptake, often in cold weather and when water supplies are too variable. I do see a little BER on our first hoophouse tomatoes to ripen, but the plants quickly grow out of it as the weather warms up.  The photos of young yellow squash Emily Zobel showed  looked just like what I have been thinking was lack of pollination!! Now I will need to see if encouraging the plants to take up more calcium can solve the problem. This “actionable nugget” arrives in good time for this growing season!

I also learned that duct tape can be used to remove squash bug eggs. (I’d given up trying)

Yellow Shoulders on Hoophouse Tomatoes

Hoophouse tomatoes with yellow shoulders. Glacier or Stupice.
Photo Pam Dawling

From a workshop on Organic Soil Management for High Tunnels at the Southern Sustainable Agriculture Working Group Conference, presented by Krista Jacobsen, I learned some valuable tips about dealing with salt build-up in hoophouse soils. – she referred to hoophouses as “irrigated deserts”!

I also learned  about yellow shoulders on tomatoes. Previously I had read that the green/yellow shoulders were (unfortunately) genetically linked to good flavor in some varieties. At this workshop I learned that yellow shoulders (as opposed to green), can be a sign of potassium deficiency. Temperatures above 90F can also be a factor. The determinant hybrids have less of a problem than other varieties. Excess magnesium can be a factor, as can the choice of variety, a virus infection, pH over 6.7. Our pH isn’t over 6.7. Ideally, the grower would increase the magnesium to calcium ratio to 1:6 or 1:4, and/or increase the potassium. Perhaps we are short of magnesium. I will need to study our soil tests more carefully.

Organic Weed Management

A carpet of weeds, but the crop is easily seen!
Photo Bridget Aleshire

In this SSAWG workshop by Daniel Parson, I learned a technique for training newbies on weed control: Make them get down on the knees and point to and touch the crop plants before hoeing or pulling weeds. He says : “If you can see the weeds without getting down on the ground, you’ve waited too long! ” Weeds should be dealt with while tiny. Bring your trainees back in a week to to see the results of their hoeing. I like this idea! Too often it is hard for new workers to learn from their experience because they don’t study and critique their work as they learn!

Lean Farm Ideas

Ellen Polishuk gave this workshop, and I went because I had both enjoyed and been challenged by Ben Hartman’s Lean Farm book. I wanted to hear someone else’s perspective and remind myself of the best bits. To my surprise, one idea that stuck out was to work in 90 minute chunks, with short breaks (or longer meal breaks). I’m not sure I fully embrace this idea, but I’m mulling it over.

March Events

I have two events in March, where I am making presentations. The first is an online conference (no travel costs!)

 

CSA Expert Exchange:
An Online Conference
Presented in partnership with Small Farm Central
March 6 – Want to Start a CSA?
Beginning Farmers Session
7:00pm-9:30pm EST
March 7 – CSA Expert Exchange Main Event
11:00am-3:30pm EST

Register for one or both days. Sessions will be recorded.
I am speaking on Crop Planning on Friday at 1.40pm.
Then on Sunday March 16, is the rescheduled day at Lynchburg College (postponed from February 15 because of all the snow). I am speaking on Feeding the Soil.
Ira, Cindy and Pam working on our presentations
Ira, Cindy and Pam working on our presentations. Photo Betsy Trice

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