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).