I would do both. I would start some outside to see if they could survive, and some inside as well because if the outside ones don't survive, you'll still get some cabbage. If they do end up surviving the cold, you'll have double the cabbage.

Either way, you'll know how tolerant they are so you won't have this question next year.

Surviving days in single digits is pretty darn cold hardy as far as I'm concerned

That was well established plants in soil that had been warm all summer, not freezing cold for weeks.

There are 2 different issues to consider - air temps vs. soil temps. While the adult plants themselves may be cold tolerant once they are established, very young, just germinated seedlings and the seeds are not.

So when it comes to direct seeding it is soil temps, not air temps that count for germination. The soil must be warm enough for the seeds to germinate without rotting or freezing first. And then air temps have to be warm enough until the seedlings get established.

That high incidence of extremes in early spring is why most cole crops are transplants, not direct seeded.

But as Homer said, try it for yourself to see which works in your garden. That is the best way to learn. ;) Meanwhile some research into soil temperatures and their relationship to seed germination can be a wealth of information for the future.

Dave

Thank you both for your responses! Looks like I'll have a fun experiment for this Spring :)

All cabbages can be in the garden even when you have freezing temperatures. But if you plant seeds when soil temperature is low, they will not germinate anytime soon.
So, if you want to get a head start, start your seeds indoor and plant them when they have some true leaves.

I have different cabbages in my garden right now. I direct sowed them in the fall. In January, so far, we have had many nights with temperatures dipping into mid teens-F. And they have not budged but have not beeing growing much either.

We raised cabbage in good soil to start and transplanted them in a new location. Transplanting seems to work well with them.

Cabbage is on my seed starting list. Being in zone 5 and with maturity ranging from 63 to 105 days, a headstart gives me earlier harvest. Most develope a sweeter taste during cooler fall nights. Frost will burn some leaves.

Your average frost date guides starting period. Trnasplants can go out three weeks before last frost if hardened off. Starting seeds allows you to select the best transplants. Most cabbage germinate in 5 to 8 days at the optimum temperature range of 70-75F. If started 4-6 weeks before setout you should be fine with one week for hardening off.

One tip for starting is repotting after true leaves. Repot with stem below the soil line and add 1/4" of sand atop potting mix to provide drainage from under the leaves.

Direct seed will give you a later second harvest; if maturity permits in a zone growing period.

One problem I haven't seen addressed yet in the discussion is the fact that every creature that moves seems to just LOVE little tiny, tender baby brassica sprouts. I've always had a lot of trouble direct-sowing any of them, because various things, from slugs and earwigs to flea beetles to white cabbage butterflies to bunnies just cant' wait to pounce.

Transplants are better, IMO, gives them at least a fighting chance.