To successfully grow milkweed, gardeners should choose a species that is appropriate for the soil type in the region, as some milkweed species prefer saturated or heavy soils, or gardeners should amend the soil as needed. Full sun is recommended for most species of milkweed.
Milkweed seeds are started indoors in gardening flats six to eight weeks before transplanting to the garden. The seeds are scattered on the surface of damp potting soil about 1/2 inch apart, and covered with an additional 1/4 inch of soil. To encourage germination, gardeners place the seeds in wet paper towels 24 hours before planting. After planting, the flat is covered with clear plastic for seven to 10 days, and the flat is placed in a warm, sunny location indoors.
Gardeners should water the seedlings by pouring water into the bottom of the flat after removing the plastic. Before transplanting the seedlings, gardeners place the flats containing the seedlings outdoors in a sheltered location for several hours each day. After several days, the seeds are transplanted.
Gardeners should refer to the plant species to determine how to space the plants. Milkweed is fertilized two to three times during the growing season with a water-soluble fertilizer, and the seedlings are thinned as needed beginning one to two weeks after planting outdoors.