Ellen, there are more than 100 milkweed/butterfly weed, but most need at least a month cold stratification. One of the few exceptions is Asclepias speciosa, that one germinates without.

I just checked the package I got in trade, it doesn't say the species, so I will wait until winter.
Thanks.
Do you have any experience with sowing butterfly weed seeds that are 2 or 3 years old?

I can't answer the question about older seeds, but I can give you a little info about my experience this year.

I sowed a couple dozen butterfly weed seeds (I got them from Prairie Moon) this winter (mid February) in milk jugs. About half of them germinated. I transplanted them into small pots after the second true leaf emerged. They were tiny at this point, and I think it was perhaps early May by then as we had had a longer winter than usual. Not long after that I moved them into the garden. I was a little worried that if I left them in containers too long I'd damage the taproot when moving them.

Around the same time I planted a couple of larger ones I'd purchased in containers from a nursery. One of these died about a month later, and the other looks anemic compared to the ones I wintersowed.

The wintersown seedlings grew slowly until late June or so and have been doing well since then. Most of them have two or three main stems that have been bent down quite a bit by winds (possibly the soil is too rich as well). I've propped a few of them up with stones.

I was surprised that some of them are flowering now in their first year. The attached photo was taken this morning.

Pretty seedlings woodstea. I will usually have 1 or 2 butterfly weed seedlings that flower the first year. All 5 of my seedlings that sprouted last year bloomed well this year, and some are setting seed. :)

Ellenr did you get that seed from me? I think we did a SASBE last winter. My experience with Asclepias tuberosa is that is does NOT need cold stratification. I've sown it twice over the past 6 years in Spring and it sprouts very well.

My first year wsing (2008) I got some milkweed seeds in trade, that were supposed to A. curassavica (tropical). I sowed them in April. Much to my surprise, they weren't tropical, they were A. tuberosa. They sprouted abundantly with the other annuals without cold stratification.

Do you think you want to try sprouting some now? If you start seedlings now, I would over-winter them inside a cold porch or garage. That's what I do with smaller plants, summer seedlings, and tender or borderline hardy babies, or special plants like my Salvia Black & Blue. I figure they might not make it over the winter and this works well!