Welp, yesterday I brought everything out--including the scarlet flax sprouts by mistake. I only remembered later and then thought, well, we'll see. Not like I don't have anything to replace them. Last night we had a low in the late teens. I went out this morning and checked--the babies are still standing straight, their seed coats still hanging on like little caps on the cotelydons. No sign of damage.

I'll keep an eye on them and see whether the succession of warm days/freezing nights in store for us over the coming week or so does anything, good or bad.