The same is true for most anything supposably cold tolerant ( even kale and collards). They need to be accumulated to the 20's at least before being exposed to the teens ( or worse) all of a sudden.

Arctic cold has a bite to it that you probably don't experience very often down there in Texas.

And you can just kiss beans good bye by the time it even frosts.

Okie HU

Well, that's not true of collards. My mature collards stood up to the 15F just fine, though they were never exposed to cold before that. They wilted, but collards do that, because they move water out of vulnerable areas. But a few days later, when it warms up, they're good as new. I saw that many years ago as well.

I got some collards that are completely toasted now but it was 4 degrees up here for a day or two. And they were exposed to the 20's beforehand. There's a lot of variance in conditions.

This is my neighbor's turnips, my collards look the same or worse.

How long was your collards exposed to 15 degrees?

Okie HU

Well, actually the low temp was 15F in the morning, and the afternoon temps got up to 20F or so. That went on for two days. Wouldn't surprise me that 4F is challenging for collards. Speaking of cold tolerance, I'm blown away by garlic. Onions will start to fade at 10-15F, but garlic is happy at much lower temperatures. You'd think that all alliums would be the same, but that's not the case.

Yep. 4 degrees or lower is a challenge for anything . Even if under a low tunnel.

I got some brassicas , collards , kale , ...that took a hit from the Siberian polar air we got last week. I got some fall onions and garlic under cover too. I think collards are more cold hardy than kale , but might depend on what varieties you're growing.

Okie HU

What I learned several years ago about collards (I posted a worry here back then, and somebody reassured me) was that when collards see a very hard freeze, they wilt precipitously. You think they're goners. But what's happening is that the collards have moved water out of the cells so ice crystals won't form in the cells. That makes them look flaccid. No, all the water doesn't come out, but the concentration of sugar/organics increases in the cells, and that acts like antifreeze. When it warms up, the collards perk back up and look perfect.

It depends on how low the temps and for how long, there's a lot of difference in a very hard freeze and just plain arctic ( or the worst Siberian polar) single digit cold.

As an aside. It's getting about onion planting season for me up here.

I've had onions freeze out in the teens.

One time I put my onions in the ground in late Feb.. Then I had a late arctic plunge in early March of around 4 degrees. I had to cover with whatever I had on hand , old clothes , rugs , blankets , carpet ,then a layer of plastic over the top of it all. It made it. but what a pain in the butt.

Okie HU

I'm interested to read that you had weather warm enough for beets to have germinated this early in the year. Or had you set out plants raised inside?

I plant beets every December. As I said, down here we hardly get any serious freezes, and we might get a real freeze only every other year. Beets have no problem with that. Now, the last few years have been exceptions. Two years ago, we had a 4F freeze, and last year it got down into the teens. Wild. My understanding is that climate change is making the jet stream collapse, allowing polar air to invade. Of course, that heats up the arctic dramatically. With normal temps in the 40s and 50sF, beets take a while to germinate (maybe 2 weeks or so), but they come up. Around here, we like to plant early, in order to avoid the ferocious summer heat.

I've never tried beets during the winter months but my fall collards are pretty much shot now that they've been hit by mid-teen temps a few times. I could probably pick a few more leaves but it's slim now. My fall planted spinach on the other hand has shrugged off those teens and are now at their 2nd true leaf stage. Around mid Feb I'll thin them out, remove all weeds and a few frost bit leaves, mulch them with compost + side dress with fert. By mid March it'll be picking time.