I would treat the seeds like tropical milkweed. Since this milkweed species likes warm climates. I would not stratify the seeds. Were did you get your seeds from?

Just saw that you posted this January 2016 lol! Did your seeds germinate?

I didn't cold stratify, it being a warm climate species as you pointed out. The seeds didn't germinate (along with poor germination rates from other milkweed species I bought from the same vendor. Never again!) I finally tracked down some live ship plants from Annie's Annuals & Perennials in California. She lists it under Asclepias cancellata.

As a host plant, they didn't attract many takers, although I did have several species of western natives, some P. physocarpus, and the ubiquitous A. curassavica growing with cancellatus, all of which female monarchs preferred. As an experiment, it would be interesting to see how much action cancellatus would get if it was the only milkweed available in the area.

Is your gomhocarpus cancellatus plant growing well? How tall is it? I am wondering about growing this plant and would like to know how it grows.

Sadly, I gave all of my butterfly garden plants away before moving from SoCal to Arizona. I planted everything in containers, as the whole yard was landscaped in gravel, boulders, cacti and succulents.

Before moving, I did grow several for a couple of seasons, eventually attaining a height of around 2 - 2½ feet. I'm sure they would have been taller if planted in the ground.

They grow very slowly until daytime temps consistently reach 80° f. After that, they grow fairly rapidly. The leaves are very thick and leathery and not very large. The plant as a whole is more succulent-like. Don't overwater if you decide to grow it! Also, it exudes TONS of milk sap at cuts, so be careful if your skin is reactive to it. All in all, I enjoyed having them around. I did find several cats on them over the course of time, but they all eventually disappeared, most likely due to predation. It's more of a stiff, open plant, so there's not much cover for them as found in milkweeds such as A. fascicularis. Growing cancellatus in the ground may allow them to grow bushier as opposed to taller, thinner plants container grown.

Below is a close up of leaves that may give you an idea what to expect. BTW: the green spider mimicked the plant's color so well, I really had to look hard in order to spot him.

I did propagate it using cuttings and a heat mat, getting about 50% success. It probably would have been higher if I kept the growing medium a little drier.

Let us know how you fare if you decide to grow some Will!