Seeds from Halls Milkweed Asclepias Hallii. These blossom in zones 4-11 throughout the season and will bring more butterflies than you can imagine. These plants are perennials and grow in full sun and sandy soil is best for them. Quite a drought tolerant plants and is a real attracion to the garden with its soft lavenderish blossoms. 4-6 weeks of stratification suggested for good germination.