It gets worse (better). you can pick them frozen and if thawed slowly, they will be as good as picked fresh. They are my sole January-February fresh food from the garden (tunnels), I have done it a number of times. My best guess is that the combination of high leaf sugars and thick leaves protects them better than most other crucifera. They truly are an unique veggie. super-nutritious, too.

Concur: It takes single digit temps to hurt collards. Plus they have much better flavor after a hard freeze. They sort of use sugars as antifreeze.

But my question was that if collards can endure single digit temps, why did they look unhappy after 23F? My beets were completely unperturbed.

Thank you. That's very fascinating. Never knew that!

Lazy is correct. Next time they will look crisp. But they tend to sacrifice the older, outer leaves after a freeze. Not really an issue, given the abundance you have and given that those are the worst eating ones.

I also got the drooping Collard leaves at 26F recently. I find Collards to be hardier than Kale as the former generally makes it through our relatively mild winters and makes a nice Spring bonanza while the Kale more than likely is miserable. Although the Kale can also make a decent harvest of excellent flower sprouts in Spring. Anyway, we rarely get single digit temperatures around here, but when we have, my Collards are history.

You would think that when people talk about the cold tolerance of collards, this would be explained. As in, "they won't get killed, but they'll have you worried for a few days!" What other "cold tolerant" plants show this behavior? Yes, I've heard that collards are doomed in single-digits.

My mustard greens survived temperatures as low as 9F. The bigger leaves are wilted, but the smaller plants look unharmed. The ground was frozen pretty hard. Just to throw that in the knowledge bank.

"What other "cold tolerant" plants show this behavior? Yes, I've heard that collards are doomed in single-digits."

Spinach, Kale, lettuce, even the wild mustard greens ... they all flatten and look droopy after a hard frost, but fluff back up in a day or so.

My leafy greens are doing fine under the frost cloth, although they looked a bit wilty at 25F. The frost cloth is keeping it moist under there, and that's critical with a 20mph dry icy wind.

I have some skepticism about frost cloths preserving humidity underneath them. If the surface of the frost cloth is below the freezing point, it'll dry out the air underneath quite effectively. All that moisture inside will end up frozen on the inside of the cloth. That's exactly how cryogenic drying technology works. Yes, the temperature in the air under the cloth can be slightly higher than freezing, but the cloth itself is pretty much the temperature of the outside air.

I predict that if you measure the humidity under a frost cloth when protecting from a hard freeze, it'll be very low.

The frost cloth does stop, or at least slow down the flow of dry air over the leaves. I think it is the air movement even more than the moisture content of the air that is important. The barrier keeps covered plants from losing as much water as plants out in the open. I think, but have no hard a data, that it is a significant difference. I know that it makes a big difference in what my plants look like. I think of it as a bit like hanging out wet laundry on a breezy day as opposed to a day with no air movement. Humidity in the air may be the same but the drying effect is not.

That may be the right way to look at it. It's not the "frost cover" that prevents drying, but the "wind cover" which is functionally the same thing. That is, a frost cover happens to block the wind also. Certainly if you have a strong wind flow, evaporation will be greater, as will cooling. If you just put a wind shield around the plants, if might be enough.

Collards under hoop houses in part shade survive -20F. I don't even have to rake off the mulching leaves to improve the thermal ballast of the system.

Just out of curiosity, what's the temperature under a hoop house when the outside temp is -20F? I assume the collards don't touch the cover.

We had temps down to 5F for several nights, with frozen ground, and my mustard greens are still alive, as well as spinach, and lettuce (!). Though, none of it looks appetizing. I am hoping the spinach at least will make it to the spring. The forecast does not look like it should at all, temps staying above freezing next week.

16F again this morning. My Collards and Kale are complete goners, and have been for some time. I'm crossing my fingers that when the snow melts my winter carrot crop (planted in Summer) will still be alive, but I think their tops will be frozen and killed. I'm not sure if a plastic sheet would have saved them or not.