The Asclepias genus contains about 140 species of herbaceous perennials, commonly called milkweeds, named for the milky sap in their leaves and stems. Many species of milkweeds are native to North America and occur in a wide range of natural habitats. Milkweeds are self-seeding, and some are also rhizomatous, so they naturalize if allowed. Most milkweeds are deciduous, but a few are evergreen. Some are tall and stout; some are low-growing and sprawling; and some are clump forming. These showy wildflowers typically bloom from spring through summer, setting long-lasting clusters of small, starry flowers in shades of white, yellow, green, purple, pink, orange, or red, borne on erect or drooping stems. Attractive seedpods follow the flowers in fall. The flowers and seedpods are both used in floral displays.
Milkweed is a nectar source for many insect pollinators and butterflies, but it is vital to the survival of the endangered monarch butterfly, as it is the host plant and the only food source for monarch caterpillars. To best support monarchs, plant milkweeds that are native to your area. The following species are generally the best for monarchs: A. asperula (antelope-horns milkweed), A. californica (California milkweed), A. erosa (desert milkweed), A. fascicularis (Mexican whorled milkweed), A. purpurascens (purple milkweed), A. variegata (white milkweed), A. verticillata (whorled milkweed), and A. viridis (green milkweed). But 3 species can be grown almost anywhere: A. syriaca (common milkweed) is the best-known species; A. incarnata (swamp milkweed) has a less aggressive spreading habit; and A. tuberosa (butterfly weed) has little to no sap. A. speciosa (showy milkweed) is drought tolerant and a good option for arid plains. However, although A. curassavica (tropical milkweed, blood flower) is beautiful, it is not native to North America and can spread disease to monarchs.
