It's not really necessary for winter sowing. If you have soaked by now though after posting this earlier, it won't hurt anything either.

Thanks- I held off sowing it until I could check

For winter sowing I don't soak anything including Butterfly Weed, Baptisia and Lupin. I get excellent germination on all of these each year.

I have soaked some vine seeds, IIRC Aristolochia and Trumpet vine. They both germinated well.

I've winter sown Butterfly weed (Asclepias tuberosa) about 3 times, and in my experience these milkweed seeds don't require pre-treatment like soaking or even cold stratification. I've sown the seeds in March and April and they sprouted fine.

Here's last year's seedlings - sown April 7th - sprouted April 26th - picture taken July 23rd.

{{gwi:455086}}