Overwintering cauliflower is right up there with giant kohlrabi as one of my favorite cool-season crops. I just want to share a quick before and after to show you how my overwintering cauli’s survived the recent Seattle cold snap.
Now, keep in mind I am a Zone 7 gardener – cold is relative. In my area, any temperatures below freezing (32 degrees F) are noteworthy, and temps in the teens for any length of time are unusual. So, I’m not suggesting this will work for gardeners in North Dakota or Saskatchewan.
But for you maritime and coastal gardeners, grow overwintering cauliflower! Seriously, check it out.
Here’s what my cauliflower looked like during the cold snap, when recorded lows were 18 degrees.
What’s going on with this? you might wonder. I mean, those plants look dead, right?
Well, to be simplistic, the cells of plants are filled with water. The biggest risk to the plant in cold weather is that, when that water freezes inside the cell it will expand. In expanding, ice crystals can rupture the cell’s wall. This is just like if you put a jar of water in the freezer and, as it froze, it expanded enough that it broke the jar. If enough cell walls rupture, the plant dies.
In severe weather, cold-adapted plants do two things to protect themselves from this risk of cell-wall rupture.
First, they throw as much sugar as possible into their cells because sugar acts as a kind of anti-freeze. This is why you will rightly hear that “frost-kissed” plants are sweeter. They really are.
Second, in more severe cold plants release as much moisture as possible from their cells. Temporarily, this is a good thing – less moisture means less threat of ruptured cells. But you also get this strange kinda “frozen wilt” look that you see like on my cauliflowers above.
Here’s my cauliflowers now, about a week after the cold snap. As you can see, they made a full recovery.
I didn’t do anything to help these guys out, either. They got no cloching, no Reemay, no row of Christmas lights under an old sheet. They were on their own and they held their own, just fine.
The Hardiest Vegetables For Winter Gardening
Winter Cauliflower is one of my favorites, but it’s not the only hardy vegetable for cold weather gardening. As you think ahead to what you might want to be harvesting next year at this time, keep in mind some cold weather stalwarts.
I debated where to bin Swiss Chard – somewhere between 20 and 25 degrees mine looks dead, but it consistently regrows from the root for early spring greens unless the root itself freezes solid, and that takes temps down into the teens. Also, these estimates are for winter adapted varieties – Deadon or January King cabbage, for example, as opposed to quick and tender summer coleslaw varieties.
Practically Unkillable (will survive down to 10 degrees F or colder) – Chives, Collards, Corn Salad/Mache, Garlic, Horseradish, Sunchokes, Kale, Leeks, Onions, Parsley, Parsnip, Rhubarb.
Very Hardy (will survive down to 20 degrees F or colder) – Sprouting Broccoli, Brussels Sprouts, Winter Cabbage, Winter Cauliflower, Celery, Daikon, Spinach, Rutabaga, Winter Kohlrabi, Arugula, Swiss Chard.
Hardy (will survive down to 25 degrees F or colder) Beets, Carrots, Fava Beans, Lettuces, Celeriac, Fennel, Mustard Greens.
Cold Snap Tips
Never pick veggies while frozen. Wait until the cold snap passes and they can thaw out naturally and on their own. Exception: if you have heading (not sprouting) broccoli or cauliflower in floret, you might as well pick the florets even if they are small- when the florets freeze they tip-brown and often start to rot after they thaw.
Don’t yank roots on greens like chard and frisee just because leaves die back – the plant will often resprout and provide you with the earliest spring greens in the neighborhood.
Some winter veg will look ugly at temperatures that will not kill them. Don’t be discouraged. Many root crops will lose their leaves when it gets much below 28, but the roots themselves are still fine and harvestable. Stuff like cabbage and Brussels Sprouts may need to have a layer or two of wrapper leaves removed but should be tasty underneath.
It might seem counter intuitive but snow in the Pac NW is an insulator – it actually keeps the ground warmer than it would otherwise be. Heavy cloud cover also helps trap whatever heat can build up in winter – I call it the sky cloche.
How did your garden come through this recent cold snap? Did you lose any crops?
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Excellent article. The information is very clear and concise. I am also in Zone 7 and do 4 seasons gardening regularly. I find the broccoli is especially tasty. We occasionally have minus temps and I throw a couple old bedsheets over my plants for some extra protection. I rarely plant my cole crops in the spring. Fall planting is so much easier, and the end products are so good. Plus you don’t have a many problems with insects.
Totally true – I don’t worry about cabbage moth at all on these guys. It’s so nice!
I’m up in the San Juan Island area and my garden did pretty good during the freeze. It lasted about 10 days here. I did lose my Swiss Chard (more shaded area) but the Kale, Bok Choy and all my herbs are still doing great. I did have something strange happen to a young Granny Smith apple tree just before the freeze, it started blooming. It does not receive any artificial light to throw it off so I’m not sure what was going on with it. The blooms did freeze and fall off.
Hi Sheri, I’m down in Renton, cozied up next to Lake Washington and I definitely noticed wierd “spring” blooming this fall. Didn’t notice with the apple or pear trees but saw it in a couple of our azaleas and some dogwoods. Another first for neighborhood (I checked with some of the old timers) was a cow elk that showed up on our property. Once the last of the pears where gone, she disappeared again, probably around late October. Its been a wierd fall that way for us.
Hi Barb, As weird as it is seeing oddities in the garden I’m glad I’m not alone. On the back of my mind is Fukushima. Praying it’s not a bi-product of radiation making plant imbalance and ill health.
I’m still struggling to find the right planting time for my winter cabbage in Seattle. Too early and it bolts; too late and it doesn’t size up before the winter. Where is the sweet spot?
I start mine in big 4″ pots between July 1 and 15th, depending on the year and when I get to it, then transplant out mid August into areas vacated by spring crops. I do long maturing Brussels Sprouts even earlier – June 15 is my target day for those because they seem to take forever.
This gives me hope. I hadn’t gotten around to harvesting the last 2 purple cabbage in my (zone 5) garden, before we got our cold snap and then snow. So it sounds like they might possibly be edible, if we actually get a warm spell. I do have to laugh at your definition of weather for Practically Unkillable at 10 degrees – we’ve already had single digit weather here in northern Illinois!
Single digit stuff is…..well….I honestly can’t remember ever seeing temps in the single digits in my garden. I’m near Puget Sound, so even more mild than inland Pac NW gardeners. My friends up in the foothills get down that cold.
Two weeks ago, everything was frozen and looking horrible. Now, all of our greens have rehydrated, the peas and cabbages are flowering again, and lettuce seedlings from seeds planted just before the freeze are coming up. Gotta love the PNW “cold” season!
Whoot whoot!
Do you get fewer problems with cabbage worms and other pests with winter cauliflower? Had a good crop this summer with spring starts from a nursery but I was battling pests most of the time… (this was my first year with a “real” garden)
Christmas tree lights in the garden-why have I never heard of that?!! Would the new LED lights (that put out hardly any heat) work or would they have to be the old-school variety?
I may need to run electric out to the garden now-Hubby keeps putting a nix on my Griswold-ish house decorating desires but he has no control out in the garden! *cackles gleefully*
I’d go old-school if you have them. Those lights put out a lot more warmth. Rope light works well too.
Oh sometimes I dream of moving to a warmer climate for gardening!
I’ve been doing lots of overwintering experiments the past couple of years. Mostly accidental at first, with lazy fall garden clean up, then I was ever so surprised to see kale re-sprout in the spring . I decided this winter would be the year I would really push some limits, of course mother nature is laughing at me now, it’s the coldest it’s been in YEARS -20C/-4F.. so.. yea.. I would be really amazed if something survived, especially with very little snow to act as a blanket. We’ve had success with kale, savoy cabbages, garlic, chives/other herbs, and spinach overwintering here and giving us food in the spring. This past fall I left many broccoli, cauliflower and some cabbages for experimental overwintering. We shall see!
Negative 20C/4F?! Holy crikey. You’re in BC, aren’t you? That’s super cold for that area.
Yes B.C , in the mountains, although more interior and not as cold as the rockies. Usually it doesnt get much colder than -10C/14F and often hovers around 0/32F, so overwintering has gone pretty good so long as we have deep snow. I tried leaving some baby spinach & swiss chard with heavy weight row cover this winter as an experiment too.
Headin to Alberta next week though, a week ago it was *gasp -40!!!*
Zone 5 Midwestern Tundra. We hit -8F (-22C) last week the same morning the furnace quit. Took some quick rethinking of our home heating plan but thanks to drapes, candles, a kettle of water on the gas stove, and a single electric space heater were able to bring the inside temps up so the water pipes weren’t in danger until the repair guy could stop by.
When we ‘overwinter’ the garden we cover it in ground leaves and compost and kiss it goodbye until spring. 91 more days … but who’s counting?
Great information.. will make next mid summer planting so much easier….no brain pain 🙂 I’m here in PNW, between Sea and Tac, and I though we were having a night or two near 32, then was in shock as the days rolled on, with nights in the 20’s!! I figured, too late to protect, with already-frozen ground. By the time it thawed, I remembered I had a mountain of (free) burlap sacks, thanks to Dillano’s in Sumner, that I could have tossed around. I’m going to pay more attention to freeze warnings in the future, and spread the jute around ahead of time. I’ll probably be responsible for no future warnings ever materializing 😉
So glad to know that the garlic (‘Music’ on your recommendation) I planted in ‘holding’ pots will likely be sprouting with the first warmish weather 😉
I could use the piles of leaves I ‘harvested’ this fall, but that requires also covering with fencing to prevent blowing away. BTW, I’m new to burlap, and looking forward to finding many uses for it… starting with the ‘Interbay compost method’.
I have a problem with wind blowing my leaves away up here in the San Juans so they have to go into a compost bin. I was the very lucky recipient of used sailboat sails. They make great greenhouse and row covers. Maybe leave a card posted at a local marina or canvas/sail shop and see if someone needs to clean some old ones out from under their crawl space?
I can’t bring myself to tear out the Lacinato kale “trees” that have been growing in my P-Patch here in Seattle for nearly a year, because they just won’t stop producing … Even after the weird fall season, which brings those gross feathery things (scientific term) on the leaves, they’ve been troopers, and I even picked a bunch during the recent freeze (they thawed within minutes and were fine). I’m also overwintering a bunch of onions and garlic, plus the three-year-old sorrel-that-will-not-die.
I feel the same way about my kale. They manage to still put on those young leaves at the top that I can snip & toss into the soup pot. I found out a couple years ago that Walla Walla Sweets winter over very nicely, missed a few at harvest time a couple years ago. Had a bumper crop of white onions this last year, beat the Walla Walla’s. The red onions I planted just didn’t grow much so I use them in stews and soups.
This is really, really helpful. My salad burnet is also surviving so far. And I have had an idea, which is to use up all my leftover seeds from last year for winter microgreens. Am proud of this idea. The main things to NOT do microgreens of, are the nightshades (and I guess rhubarb), but the brassicas are all very cool for this, and alliums, and some of the lettuce and cress.
What a cool idea! I wish I had tried this.
My greens/radishes made it through okay, but my artichokes look like they’re toast! I mulched around their bases with compost and straw and tied them up per the instructions I’d received. Then I go to check on them after the snow fell and I’m not sure I’ve ever seen more frozen, shriveled, miserable looking creatures in my life.
I really hope they pull through, this next season is the season where they’d finally become crazy productive. 🙁
Salem, Oregon here. My 3-inch fava beans, purple sprouting broccoli, arugula and escarole made it through the long freeze just fine. Just draped them with heavy plastic for the duration.
I was shocked this fall when everything in my garden died back at the hard frost except parsley and chives. I had no idea those things were so durable! NW MT here though, so after a week of sub-zeros, even those are well and truly dead now I’m pretty sure.
I probably missed it but please tell what variety you have grown in the two pics above. Thanks 🙂
ALERT for any PNW gardener who has trouble growing just about anything:
The first thing that I ask people is if they know whether or not they have symphylans in any of their beds. These creatures can make gardening a soul-killing experience. There are particular crops they love, and those are many. I didn’t find any symphylan references when I searched NW Edible, so I suggest a symphylan collaboration, to get the word out. One can become convinced one is are a terrible gardener when everything comes out bonsai, (or just everything except potatoes, in a particular bed) but it may not be your fault!
I only use DE (Diatomaceous Earth) to battle bad insects in my garden. Mostly sowbugs, earwigs, slugs & snails and I powder my fruit trees with a jelly bag filled with DE if I find aphids. What have you used to control “symphylans” ? Is it non-toxic to humans? I do have several different species in my garden, mostly visible when I check under pots for hiding slugs. I never thought they might be doing damage to my garden.
Thanks for this article, my kale looks super wilted and dead right now just like your cauliflower did (I’m in the greater Seattle area) and I was getting worried. Glad I could look this article up quickly by searching for “overwintering kale seattle”… I’m grateful for the education. Thanks again.
This is a very informative article. I did not know in zone 7 we could plant cole crops for the Spring. Was looking to see if it was too late to plant some turnips and a few beets. Not a problem when it come to the greens, but wondered how they would do after a hard frost in our area. I may decided to link your article to my blog someday when I have time to blog … it is seasonal for me at times.