This plant is very easy to start from seed! When the pods are swollen nicely, you can get ready to collect seeds. The seeds will not blow away right after the pod opens, but you don't want to wait very long! I can't tell which kind of asclepias you have (tuberosa or curassavica) but one needs the seeds to be cold stratified before sowing and the other, not. If you do not know which you have, I suggest that you do one batch of each to hedge your bets.