endive – Sustainable Market Farming

Winter-Kill Temperatures of Cold-Hardy Vegetables 2020

Overwintered Vates kale in central Virginia in March.
Photo Nina Gentle

At the Organic Association of Kentucky Conference, I gave a a presentation on Winter High Tunnel and Outdoor Vegetable Production. You can see it here. Click on the diagonal arrow icon to see it full screen, then click on the right pointing triangular arrow

Winter vegetable production outdoors and in a hoophouse Pam Dawling from Pam Dawling

Winter-Kill Temperatures of Cold-Hardy Vegetables 2020

I keep records of how well our crops do in the colder season, both outdoors and in our double-layer hoophouse. I note each increasingly cold minimum temperature and when the various crops die of cold, to fine-tune our planning for next year. We are in zone 7a, with an average annual minimum temperature of 0-5°F (-18°C to -15°C).

The winter 2019-2020 has been mild, with our lowest temperature being a single night at 12°F (-11°C). The Koji became completely unmarketable but did not completely die. Yukina Savoy is indeed hardier, 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).

This 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.

In early January 2018, we had some extremely cold temperatures of -8°F and -9°F (-22°C and -23°C). The winter of 2018-2019 was not as brutal. Our lowest temperatures were 6°F (-14°C) in late January, 8°F (-13°C) in December 2018 and a couple of 11°F (-12°C). I found that senposai is more cold-tolerant than I had thought. Averaging our winter low over those three winters gives 3.2°F (-16°C), completely within the zone 7a range.

My other results from other years still hold up.

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.

Radicchio seeds from Seeds from Italy

Notes on Chicories and Endives

We gave up growing chicories and endives because we really didn’t like the bitterness. I decided to do some more online research to make sure I wasn’t spreading untruths. Chicories and endives fall into two groups, but they are confusing because the common names sometimes suggest the opposite group than they are botanically. Here’s the best info I have. If you know differently, please leave a comment.

Cichorium intybus, commonly called chicories, are mostly heading crops. The group includes radicchio, both Treviso and Chioggia (hardy to about 20°F (-7°C). Belgian Witloof endive (the kind for forcing chicons) is also a chicory. It dies at 25°F (-4°C). Sugarloaf chicory is the least hardy chicory, and dies at 27°F (-3°C).

Cichorium endivia, commonly called endives, are mostly loose-leaf crops, less cold-hardy than intybus types (chicories). This group includes Frisée types and escaroles, which are also known as Batavian endives. They generally survive down to 22°F (-6°C), although Perfect and President endives can survive down to 10°F (-12°C) – can anyone confirm or deny this?

Using the List

Unless otherwise stated, these are killing temperatures of crops outdoors without any rowcover. All greens do a lot better with protection against cold drying winds. Note that repeated cold temperatures can kill 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. Your own experience with your soils, microclimates and rain levels may lead you to use different temperatures in your crop planning.

Hoophouse beds in November.
Photo Ethan Hirsh

Hoophouse Notes

Our double-plastic hoophouse keeps night time temperatures about 8F (4.5C) degrees warmer than outdoors, sometimes 10F (5.5C) degrees warmer. Plus, plants tolerate lower temperatures inside a hoophouse. The soil stays warmer; the plants recover in the warmer daytime conditions (it seems to be the night+day average temperature that counts);

In the hoophouse (8F (4.5C) degrees warmer than outside) plants without extra rowcover can survive 14F (7.7C) degrees colder than they could survive outside; with thick rowcover (1.25oz Typar/Xavan) at least 21F (11.6C) degrees colder than outside.

For example, salad greens in our hoophouse can survive nights with outdoor lows of 14°F (-10°C). Russian kales, lettuce, mizuna, senposai, spinach, tatsoi, turnips, 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.

Young Bright Lights chard.
Photo Pam Dawling

Lettuce varieties for a solar-heated winter greenhouse or hoophouse in zone 7a: (hardiest are in bold) Buckley, Ezrilla, Green Forest, Green Star, Hampton, Hyper Red Rumpled Wave, Marvel of Four Seasons, Merlot, New Red Fire, North Pole bibb, Oscarde, Outredgeous, Pirat, Red Cross bibb, Red Sails, Red Salad Bowl, Red Tinged Winter, Revolution, Rouge d’Hiver, Salad Bowl, Sylvesta bibb, Tango, Winter Marvel, Winter Wonderland.

Outdoor killing temperatures of crops (unprotected unless stated)

35°F (2°C): Basil.

32°F (0°C): Bush beans, some cauliflower curds, corn, cowpeas, cucumbers, eggplant, limas, melons, okra, some pak choy, peanuts, peppers, potato vines, squash vines, sweet potato vines, tomatoes.

27°F (-3°C): Many cabbage varieties, Sugarloaf chicory (takes only light frosts).

25°F (-4°C): Some cabbage, chervil, Belgian Witloof chicory roots for chicons, and hearts, Chinese Napa cabbage (Blues), dill (Fernleaf), some fava beans (Windsor), annual fennel, some mustards (Red Giant, Southern Curled) and Asian greens (Maruba Santoh, mizuna, most pak choy, Tokyo Bekana), onion scallions (some are much more hardy), radicchio, rhubarb stems and leaves.

Tokyo bekana in our hoophouse.
Photo Twin Oaks Community

22°F (-6°C): Some arugula (some varieties are hardier), Bright Lights chard, endive (Escarole may be a little more frost-hardy than Frisée), large leaves of lettuce (protected hearts and small plants will survive colder temperatures).

20°F (-7°C): Some beets (Bulls Blood, Chioggia,), broccoli heads (maybe OK to 15°F (-9.5°C)), Brussels sprouts, some cabbages (the insides may still be good even if the outer leaves are damaged), some cauliflower varieties, celeriac, celtuce (stem lettuce), some head lettuce, some mustards/Asian greens (Tendergreen, Tyfon Holland greens), flat leaf parsley, radicchio, both Treviso and Chioggia, radishes (Cherry Belle), most turnips (Noir d’Hiver is the most cold-tolerant variety).

Large oat plants will get serious cold damage. Oats seedlings die at 17°F (-8°C)

Canadian (spring) field peas are hardy to 10-20°F (-12 to -7°C).

15°F (-9.5°C): Some beets (Albina Verduna, Lutz Winterkeeper), beet leaves, some broccoli, some cabbage (Kaitlin, Tribute), covered celery (Ventura), red chard, cilantro, fava beans (Aquadulce Claudia), Red Russian and White Russian kales, kohlrabi, some lettuce, especially medium-sized plants with 4-10 leaves (Marvel of Four Seasons, Olga, Rouge d’hiver, Tango, Winter Density), curly leaf parsley, rutabagas (American Purple Top Yellow, Laurentian), broad leaf sorrel, most covered turnips, winter cress.

12°F (-11°C): Some beets (Cylindra,), some broccoli perhaps, Brussels sprouts, some cabbage (January King, Savoy types), carrots (Danvers, Oxheart), most collards, some fava beans (mostly cover crop varieties), garlic tops if fairly large, Koji greens, most fall or summer varieties of leeks (Lincoln, King Richard), large tops of potato onions, covered rutabagas, some turnips (Purple Top).

10°F (-12°C): Covered beets, Purple Sprouting broccoli for spring harvest, a few cabbages (Deadon), chard (green chard is hardier than multi-colored types), some collards (Morris Heading can survive at least one night at 10F), Belle Isle upland cress, some endive (Perfect, President), young Bronze fennel, Blue Ridge kale, probably Komatsuna, some leeks (American Flag, Jaune du Poiteau), some covered lettuce (Pirat, Red Salad Bowl, Salad Bowl, Sylvesta, Winter Marvel), covered winter radish (Daikon, China Rose, Shunkyo Semi-Long survive 10°F/-12°C), Senposai leaves (the core of the plant may survive 8°F/-13°C), large leaves of savoyed spinach (more hardy than smooth-leafed varieties), Tatsoi, Yukina Savoy.

Oats cover crop of a medium size die around 10°F (-12°C). Large oat plants will die completely at 6°F (-17°C) or even milder than that.

5°F (-15°C): Garlic tops even if small, some kale (Winterbor, Westland Winter), some leeks (Bulgarian Giant, Laura), some bulb onions, potato onions and other multiplier onions, smaller leaves of savoy spinach and broad leaf sorrel. Many of the Even’ Star Ice Bred greens varieties are hardy down to 6°F (-14°C), a few unprotected lettuces if small (Winter Marvel, Tango, North Pole, Green Forest).

Garlic shoots in January.
Photo Pam Dawling

0°F (-18°C): Chives, some collards (Blue Max, Winner), corn salad (mâche), garlic, horseradish, Jerusalem artichokes, Even’ Star Ice-Bred Smooth Leaf kale, a few leeks (Alaska, Durabel, Tadorna); some bulb onions, yellow potato onions, some onion scallions, (Evergreen Winter Hardy White, White Lisbon), parsnips (probably even colder), salad burnet, salsify (?), some spinach (Bloomsdale Savoy, Olympia). Walla Walla onions sown in late summer are said to be hardy down to -10°F (-23°C), but I don’t trust below 0°F (-18°C)

Crimson clover is hardy down to 0°F (-18°C) or slightly colder

-5°F (-19°C): Leaves of overwintering varieties of cauliflower, Vates kale survives although some leaves may be too damaged to use.

-10°F (-23°C) Austrian Winter Field Peas and Crimson clover (used as cover crops).

-15°F (-26°C) Hairy vetch cover crop – some say down to -30°F (-34°C)

-20°F (-29°C) Dutch White clover cover crops – or even -30°F (-34°C)

-30°F to -40°F (-34°C to -40°C): Narrow leaf sorrel, Claytonia and some cabbage are said to be hardy in zone 3. I have no personal experience of this.

-40°F (-40°C) Winter wheat and winter rye (cover crops).

Ordering seeds! Seed Viability and Varieties New to us

I’ve been busy putting our seed orders together. As we grow so many different crops, it’s quite a time-consuming process. And I hate to buy too little and be out in the field on planting day, looking at an almost empty packet. Equally, I hate to buy too much, which either wastes money (if we throw the extra away), or else causes us to risk sowing seed that really is too old, and won’t do well. I keep a chart of how long different types of seed last:

Seed Viability

(From Sustainable Market Farming, (c) Pam Dawling, New Society Publishers, 2013)

“Opinions vary a bit about how many years seeds of different vegetables are good for. The fuller story is that storage conditions make a big difference. You can make your own decisions, weighing up the information supplied, your knowledge of how carefully you stored the seeds, the information on each packet about percentage germination when you bought it, and the economic importance to you of that particular crop. If you always transplant lettuce, as I do, you can risk one of your four varieties in that sowing coming up poorly, and just plant out more of the other three if it fails. Many seed catalogs include information about seed longevity, and so does Nancy Bubel in The Seed Starters Handbook.

www.chelseagreen Frank Tozer in The Organic Gardeners Handbook has a table including minimum, average, and maximum.

A simplified version is as follows:

Year of purchase only: Parsnips, Parsley, Salsify, and the even rarer Sea Kale, Scorzonera
2 years: Corn, Peas and Beans of all kinds, Onions, Chives, Okra, Dandelion, Martynia,
3 years: Carrots, Leeks, Asparagus, Turnips, Rutabagas
4 years: Spinach, Peppers, Chard, Pumpkins, Squash, Watermelons, Basil, Artichokes and Cardoons
5 years: most Brassicas, Beets, Tomatoes, Eggplant, Cucumbers, Muskmelons, Celery, Celeriac, Lettuce, Endive, Chicory.”

Rather than deteriorating with age, some very fresh seed has a dormancy that needs to be overcome by chilling (lettuce). Other seed contains compounds that inhibit germination. These can be flushed out by soaking in water for about an hour (beets).

Another of the challenges with seed ordering is converting between grams, ounces and seed counts. Here’s a helpful table of 1000 Seed Weight for 13 crops.

Our main seed suppliers are Fedco, Johnny’s and Southern Exposure. Fedco has great prices, especially on bulk sizes, great social and political commentary in the catalog, and no glossy pages. Johnnys has some good varieties that Fedco doesn’t, and a ton of useful information tucked away on their website. Southern Exposure is best on southern crops and heat tolerant varieties which we can’t expect seed companies in Maine to specialize in. Plus, SESE are my friends and neighbors.

This year we are trying some new varieties. Generally we like to have some reliable workhorses that we know well, and trial a few new things, especially if we hear our favorite varieties are no longer available. Last year our Nadia eggplant couldn’t cope with the heat. For a while in early summer they didn’t grow at all – no new flowers, never mind new fruit. So next year, alongside Nadia I’m trying 3 that should deal better with heat. Florida Highbush is open-pollinated, from the Seed Savers Exchange. Epic and Traviata are hybrids from Osborne Seeds.

Florida High Bush eggplant from Seed Savers Exchange

Sugar Flash Snap Peas from Osborne Seeds

I also bought some Sugar Flash snap peas from Osborne. We have been big fans of Sugar Ann, but I’ve heard Sugar Flash is even better on flavor, yield and harvest period. We’re going to find out!

For a couple of years we really liked Frontier bulb onions as a storage variety for this climate and latitude (38N). Frontier disappeared from the catalogs of our usual suppliers and we tried Gunnison and Patterson. This year – no Gunnison! And we didn’t get a good test of Patterson last year, as we failed to weed our onions enough, after an initial enthusiastic good go at it. We were looking again at Copra, one we grew some years ago (before we found Frontier). I lucked out when I decided to see if Osborne had Gunnison, while I was shopping there. they didn’t, but they had Frontier! And then when I was shopping at Johnny’s, I found they did have some Gunnison for online sales only. So I ordered those too!

We’re also trying Sparkler bicolor sweet corn from Fedco and a drying bean I won’t name, as the seed is in short supply. And this year we’re hoping Red Express cabbage will prove to be a reliable little worker. We used to like Super Red 80, but had several years of poor results. Since then, none of the other red cabbages we tried have satisfied us in terms of size, earliness, productivity and flavor.

West Indian Gherkin Seeds (Cucumis anguiria) from Monticello

After a few years of poor pickling cucumbers, we’re going outside the box and trying West Indian Gherkins from Monticello, where they were grown by Thomas Jefferson (and some of the enslaved people, no doubt). These are not closely related to actual cucumbers, but are used similarly. I saw them growing in the Monticello garden when I was there for the Heritage Harvest Festival in September, and they are certainly robust and productive in hot humid weather. We’ll see how the pickles turn out!

My only other “impulse buy” was the Salanova Lettuce new at Johnny’s. They are 6 varieties of head lettuce designed to be used for salad mix at a single cutting. Quicker than snipping rows of baby lettuce with scissors. More fun than plain lettuce heads. They are loose heads of small leaves in various shades of green and red, and two “hairstyles”: frizzy and wavy.

Salanova Lettuce from Johnny's Seeds — Salanova Lettuce from Johnny’s Seeds

Winter Hardiness

It can be hard to find out just how cold a temperature various vegetable plants can survive. Reading books written in different parts of the country can be confusing: “survives all winter” is one thing in the Pacific Northwest and another in Montana. So for some years I have been collecting data and exchanging information with my friend and neighbor Ken Bezilla at Southern Exposure Seed Exchange. Each winter I try to record what dies at what temperature. Below is my current list, which should be treated as a work in progress.

Your own experience with your soils, microclimates and rain levels may lead you to use different temperatures. If you have data from your garden, please leave a comment. Likewise if you have found particular varieties to be especially cold-tolerant, I’d love to learn more. Central Virginia isn’t the coldest spot in the US, but if I can grow something without rowcover, I’m happy to hear it!

Here’s our temperature list at which various crops die:

35°F (2°C): Basil.

32°F (0°C): Bush beans, cauliflower curds, corn, cowpeas, cucumbers, eggplant, limas, melons, okra, some Pak Choy, peanuts, peppers, potato vines, squash vines, sweet potato vines, tomatoes.

27°F (-3°C): Most cabbage, Sugarloaf chicory (takes only light frosts), radicchio.

25°F (-4°C): Broccoli heads, chervil, chicory roots for chicons, and hearts, probably Chinese Napa cabbage (Blues), dill, endive (hardier than lettuce, Escarole more frost-hardy than Frisée), annual fennel, large leaves of lettuce (protected hearts and small plants will survive even colder temperatures), some mustards and oriental greens (Maruba Santoh, mizuna, most pak choy, Tokyo Bekana), onion scallions, radicchio. Also white mustard cover crop.

22°F (-6°C): Arugula, Tatsoi. (both may survive colder than this.) Possibly Chinese Napa cabbage (Blues), Maruba Santoh, Mizuna, Pak Choy, Tokyo Bekana with rowcover.

20°F (-7°C): Some beets, cabbage heads (the insides may still be good even if the outer leaves are damaged), celeriac, celtuce (stem lettuce), some corn salad, perhaps fennel, some unprotected lettuce – some OK to 16°F (-16 °C), some mustards/oriental greens (Tendergreen, Tyfon Holland greens), radishes, turnips with mulch to protect them, (Noir d’Hiver is the most cold-tolerant variety).

17°F (-8°C): Barley (cover crop)

15°F (-9.5°C): Some beets (Albina Verduna, Lutz Winterkeeper), beet leaves, broccoli leaves, young cabbage, celery (Ventura) with rowcover (some inner leaves may survive at lower than this), cilantro, endive, fava beans (Aquadulce Claudia), garlic tops may be damaged but not killed, Russian kales, kohlrabi, perhaps Komatsuna, some covered lettuce, especially small and medium-sized plants (Marvel of Four Seasons, Rouge d’Hiver, Winter Density), curly leaf parsley, flat leaf parsley, oriental winter radish with mulch for protection (including daikon), large leaves of broad leaf sorrel, turnip leaves, winter cress.

12°F (-11°C): Some cabbage (January King, Savoy types), carrots (Danvers, Oxheart), multi-colored chard, most collards, some fava beans (not the best flavored ones), garlic tops if fairly large, most fall or summer varieties of leeks (Lincoln, King Richard), most covered lettuce (Freckles, Hyper Red Rumpled Wave, Parris Island, Tango) , large tops of potato onions, Senposai, some turnips (Purple Top).

10°F (-12°C): Beets with rowcover, Purple Sprouting broccoli for spring harvest, Brussels sprouts, chard (green chard is hardier than multi-colored types), mature cabbage, some collards (Morris Heading), Belle Isle upland cress, some endive (Perfect, President), young stalks of Bronze fennel, perhaps Komatsuna, some leeks (American Flag), Oriental winter radish, (including daikon), rutabagas, (if mulched), tops of shallots, large leaves of savoyed spinach (more hardy than flat leafed varieties), tatsoi, Yukina Savoy. Also oats cover crop.

5°F (-15°C): Garlic tops if still small, some kale (Winterbor, Westland Winter), some leeks (Bulgarian Giant, Laura, Tadorna), some bulb onions (Walla Walla), potato onions and other multiplier onions, smaller leaves of savoyed spinach and broad leaf sorrel.

0°F (-18°C): Chives, some collards (Blue Max, Winner), corn salad, garlic, horseradish, Jerusalem artichokes, Vates kale (although some leaves may be too damaged to use), Even’ Star Ice-Bred Smooth Leaf kale, a few leeks (Alaska, Durabel); some onion scallions (Evergreen Winter Hardy White, White Lisbon), parsnips, salad burnet, salsify, some spinach (Bloomsdale Savoy, Olympia, Tyee). Also small-seeded cover crop fava beans.

Even Colder: Overwintering varieties of cauliflower are hardy down to -5°F (-19°C).

Many of the Even Star Ice Bred varieties are hardy down to -6°F (-20°C).

Walla Walla onions sown in late summer are hardy down to -10°F (-23°C).

Winter Field Peas and Crimson clover (used as cover crop) are hardy down to -10°F (-23°C).

Hairy vetch and white Dutch clover cover crops are hardy to -30°F (-34°C)

Sorrel and some cabbage (January King) are said to be hardy in zone 3, -30 to-40°F (-34 to -40°C)

Winter wheat and winter rye (cover crops) are hardy to -40°F (-40°C).