Here in northeast Ohio, the two most common species are common milkweed (Asclepias syriaca) and swamp milkweed (Asclepias incarnata). If you would like to try your hand at harvesting some milkweed seeds, do so before the pods open and begin releasing their contents. Like many seeds, those of milkweed require cold stratification, a period of cold which helps to break the dormancy of the seeds so that they can germinate in the spring.