How big were they when they froze? Once they reach a certain size, they are likely to bolt if they froze, but if they were really small, they ought to regrow. However, Brussels sprouts have a hard time producing the sprouts before the heat sets in. I sometimes can get a crop from them if I put 5-week old plants in the ground around mid- to late-January. Otherwise, I just save them for fall planting because the heat tends to arrive right when they are about to bloom----and then they immediately bolt in spring.

Thanks. I noticed this am that several collards are flowering. I don't know what variety the sprouts were or the broccoli, so don't want to save seeds from them. They were plants.

It just figures that they'd flower so early.

It is hard to prevent overwintered brassica crops from flowering early as they are biennials so that is their nature. Sometimes, if the very cold weather arrived in fall just after you planted them and they don't grow much, they can remain tiny and stunted all winter and start growing normally again as early as late December or early January. Sometimes when that happens, they might have time to make a crop before the daylength triggers bolting.

I have had all sorts of mixed results with overwintered cool-season crops bolting. Sometimes overwintered Swiss chard will bolt, but other times it never bolts and lives for a couple of years. Sometimes overwintered kale bolts early but other times it bolts much later. I cannot necessarily find a reason, but think it likely is related to temperature and stress. My lettuce that sprouted voluntarily (from self-sown seeds from last year's spring crop) looks really nice right now, but from experience I know it will bolt at some point this spring. By then, though, I hope the new seeds I just planted recently will have produced plants large enough to harvest from instead.

I at least have a marker that says Georgia collards, so I think I can save seeds. The ones flowering were in pots all winter, never got real big, but they sure survived some bad weather, so I will plant some in the fall. I have some lettuce that lived all winter that I wish would bolt, I want seeds from it!

The lettuce will bolt. Just be patient and give it time. I let the lettuce plants bolt on purpose and don't collect the seeds. I leave the seeds for the goldfinches. They love them, but they never get them all, so I get volunteer lettuce seedlings every year. Often, those seedlings grow faster and better than lettuce plants that I raised indoors from seed even though they sprouted later.