Seeds from this Antelope Milkweed Milkweed Asclepias asperula. These cream colored blossom are hardy in zones 4-11 and will bring more butterflies than you can imagine. These 24 inch plants are perennials and grow in full sun and sandy soil is best for them. This is one plant that can be covered with at least three types of butterflies at one time. 4-6 weeks of stratification suggested for good germination.