Knowing at what temperature various frost tolerant vegetables will die, and watching weather forecasts will help us act in time to save our crops.
I’ve long been interested in just how cold-tolerant various vegetables are. Each spring I update my Winter-kill list of cold-hardy crops. You can find Winter Kill Temperatures of Cold-Hardy Vegetables 2019 at the link. Here I’ll describe some step-by-step observations as temperatures dropped one winter.
14 Degrees Fahrenheit (-10C) in mid-December
A few years ago (in the 2013-2014 winter), we had two nights at 14F (-10C) and several others in the teens in December. What survived that temperature? We had Tyee spinach under rowcover, and Vates kale in the open. The senposai was still alive, but some of the midribs had brown streaks. Sadly we didn’t have any leeks that winter, as we lacked enough workers to tend them in late summer. Still alive were a nice bed of Deadon cabbage intended for January harvest, and some small heads of Melissa savoy that missed the bulk fall harvest. The Gunma cabbage stumps had some leaves and tiny heads still alive, but the Tendersweet were definitely dead. We had cut off all the chard leaves in November, and it seemed to be dead. Some winters it hangs on later, if we leave some foliage to help it regenerate.
The oats cover crop we sowed in August and early September was pretty much dead. All the broccoli looked dead. That’s as expected for the temperatures. Often we don’t get nights this cold till January – the cold came early that winter.
The hardneck garlic tops looked to be in good shape. The Polish White softneck tops were considerably smaller, but they had suffered a bit. They will grow back if they have died. Some of our Chandler strawberry plants looked dead. Either that or they were extremely dormant! The deer were killing them off by eating the leaves. Too many deer!
The hoophouse was still bursting with great food. Plenty of salad greens: lettuce; various kinds of mizuna and frilly mustards like Ruby Streaks and Golden Frills, as well as Bulls Blood beet leaves. And for salads or cooking we had spinach, chard, tatsoi, radishes, scallions, baby Hakurei turnips and their tasty greens, Red and White Russion kales, and more senposai. In January we eat the heading Asian greens: pak choy, Chinese cabbage, Tokyo bekana and Yukina Savoy. The first sowing of tatsoi (9/7) was starting to bolt, so we cleared that. The first round of baby lettuce mix (10/24) was ready for its second cut. I love working in the hoophouse on sunny winter days.
4 Degrees Fahreheit (-15C) in Early January
Second: two nights at 4F (-15C) in early January. Along came the Polar Vortex, which in our part of central Virginia, meant two nights at 4F (-15C), January 6 and 7. How did it go?
During the prelude to the Big Chill, when we got 9F (-13C), I harvested the odds and ends of small cabbages left in our main patch. Quite worthwhile, I got two 5-gallon buckets. Between the 9F (-13C) and the 4F (-15C) nights, I harvested the bed of Deadon cabbage, which we planted with January harvests in mind. There was some freeze damage, so in future I’ll say that Deadon is good down to 10F (-12C) but not lower. I got two full net bags and two more buckets of small ones from a 90′ (27.5 m) bed with two rows. I left one smaller and one larger cabbage as sacrificial victims in the cause of better information for next year. When we got 4F (-15C), the smaller one died and the larger survived. One of the other gardeners harvested the last of the outdoor senposai. Another couple of buckets of tasty food.
I took another walk round the frozen garden after the Polar Vortex, to see what was still alive. The Tyee spinach under rowcover, and the Vates and Beedy’s Camden kale without rowcover were all still alive! There was some freeze damage in spots on the spinach leaves, but plenty of good meals still to come!
Our hardneck garlic tops suffered some damage but didn’t get killed back to the mulch level. The Polish White softneck tops are considerably smaller and they too were still alive.
We had the remains of a lettuce nursery bed, still holding surplus transplants from September sowings that we didn’t need for our greenhouse or hoophouse. A good chance to see which ones are hardiest! Here’s the scoop: Still alive in the centers – Winter Marvel, North Pole, Tango, Green Forest. No longer alive – Salad Bowl, Red Salad Bowl, Winter Wonder, Red Tinged Winter, Merlot, Red Sails, Outredgeous, Roman Emperor, Revolution.
At nearby Acorn Community, the home of Southern Exposure Seed Exchange, they had some young but mature heads of cabbage outdoors. The Late Flat Dutch, Early Flat Dutch and Chieftain Savoy all survived one night at 6F (-14C). (It’s usually two degrees warmer there than at Twin Oaks on winter nights).
The Blue Ridge kale grown by Clif Slade at Randolph Farm, VSU. survived. It got down to 9F (-13C) there. Not as cold as Louisa County! Blue Ridge is taller than the Vates we grow, and I’d like to try it here, if it can survive our winters. Otherwise not!
In the hoophouse, we covered all the beds with thick rowcover on the afternoon of January 6, and didn’t roll it up for four days, after the warmer weather returned. There was a tiny bit of freeze injury on some turnip greens that poked out the side of the rowcover, and some on some stems of Tokyo Bekana. I think the rowcover saved the crops! Also, a bad thing happened. It was very windy the first cold night and the west window blew open. Argh! Of all the nights to have an open window. Memo: fix the latch to make it stronger.
I didn’t enjoy the really cold weather. I was anxious about the crops and the plumbing! But I can see two silver linings: I now have more information about cold-hardiness of various crops, and hopefully some pests will have died. Now we’re getting ready for another two cold nights, tomorrow and Wednesday.
Below Zero Degree Fahrenheit (-18C)
And third: two nights below 0F (-18C)
It got even colder. We got 0F (-18C) on January 22/23, then a few nights at 5F (-15C), and then the big insult: -4F (-20C) on the night of January 29-30. What survived that?
The Tyee spinach under thick rowcover sustained big damage, showing as patches of beige dead cells. It did recover. Meanwhile we ate the more-protected spinach in the coldframes and the hoophouse.
The Vates kale without rowcover was still alive, but badly damaged. The big leaves were crunchy and brown round the edges, and some of the inner leaves were dead. Most of it grew back, but we had to wait for a while. The Beedy’s Camden kale looked worse – the big leaves had died and flopped over. It never really recovered.
Our hardneck garlic and Polish White softneck tops were killed back to about one inch (2.5 cm) up from the mulch. Equally hardy, it seems.
In the lettuce nursery bed, still holding surplus transplants from September sowings that we didn’t need for our greenhouse or hoophouse, only the Winter Marvel showed any signs of life. So Winter Marvel gets the prize for cold-tolerant lettuce here!
In the hoophouse, we covered all the beds with thick rowcover every night it looked like dropping below 10F (-12C) inside. Almost everything survived – we only got some minor stem freezing on some turnips and Asian greens. We ate plenty of Pak Choy, Tokyo Bekana, Yukina Savoy, various turnips and their greens (Hakurei, White Egg, Oasis, Red Round), also lots of lettuce leaves, radishes, scallions, and some spinach. We had small amounts of mizuna, Ruby Streaks, Bright Lights chard, Bulls Blood beets to add to salad mixes, and Red Russian and White Russian kale growing slowly.
We are not the only people tracking the effects of the unusually cold weather. The February 2014 Growing for Market magazine opened with an article by Ben Hartman “Testing the Limits of Cold Tolerance”. He farms in Goshen, Indiana, using two double-layer plastic greenhouses heated to 30F (yes. I said heated!) and two unheated ones.
Pam Dawling has worked at Twin Oaks Community in central Virginia for more than 27 years, growing vegetables for 100 people on 3.5 acres and training many members in sustainable vegetable production. She is the author of Sustainable Market Farming and The Year-Round Hoophouse. Pam often presents workshops at MOTHER EARTH NEWS FAIRs and at sustainable agriculture conferences. She is a contributing editor with Growing for Market magazine, and a weekly blogger on SustainableMarketFarming.com. Connect with Pam on Facebook, and read all of Pam’s MOTHER EARTH NEWS posts here.
Winter Harvest Cookbook
Tantalize your tastebuds with an incredible array of soups, salads, sides, sauces, entrees and desserts such as:
- Roasted Brussels sprouts with sweet potatoes and garlic
- Penne with arugula, kale and goat cheese
- Root vegetable and leek soup with Gouda cheese
- Pot roast with hazelnut barley.
With a greatly expanded array of vegetarian and vegan dishes, Winter Harvest Cookbook is a must-have for anyone who wants to enjoy fresh, local and delicious food — any time of the year!
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