If you would like to plant milkweeds to attract bees and butterflies to your landscape, but would prefer not to plant common milkweed (Asclepias syriaca) and other species that tend to be too vigorous and weedy for beds and borders, there are manageable, attractive options.
Butterfly weed (Asclepias tuberosa) is a native Iowa perennial. It is typically found in prairie remnants and roadsides throughout the state. Butterfly weed has narrow, lance-shaped leaves, grows 2 to 3 feet tall, and flowers from June to September. The flowers are usually bright orange, but are occasionally yellow. Because of a specialized pollinating mechanism, only a few pods develop on most plants. The pods are spindle-shaped, 3 to 5 inches long, and contain numerous silky-tailed seeds. Butterfly weed has a deep taproot. The stems of butterfly weed produce a watery translucent sap when cut rather than a milky sap common to most milkweeds.
Butterfly weed is an excellent plant for perennial beds and borders. It is easy to grow, requires very little maintenance, and has few pest problems. Plants possess excellent heat and drought tolerance. Butterfly weed requires full sun and a well-drained soil. It performs well in dry soils and poor, infertile soils.
A limited number of butterfly weed cultivars are available. 'Gay Butterflies' has blooms in shades of red, orange, or yellow. 'Hello Yellow' has bright, yellow flowers.
Swamp milkweed (Asclepias incarnata) is another native perennial. It is typically found in prairie potholes, at the edges of marshes, and in wet ditches. Swamp milkweed has 3- to 6-inch-long, lance-shaped leaves, grows 3 to 5 feet tall, and blooms from July through August. The vanilla-scented flowers are pale pink to rose-purple. The flowers are followed by 3 to 4 inch pods which contain numerous plumed seeds. Stems and leaves exude a milky sap when cut or bruised.
Swamp milkweed is an excellent perennial for low sites or other moist locations in the landscape. Plants tolerate short dry periods, but prefer soils that are consistently moist or wet. Swamp milkweed prefers full sun.
A small number of cultivars are available. The individual flowers of 'Cinderella' have pink to dark pink reflexed petals and pink to white crowns. 'Ice Ballet' is a white-flowering cultivar. 'Soulmate' has deep rose pink flowers.
Prairie milkweed (Asclepias sullivantii) is similar in appearance to common milkweed. (However, it is less aggressive, and therefore a more manageable plant in the garden, than common milkweed.) Prairie milkweed is native to Iowa. However, it is far less common than the previously mentioned milkweeds. It is typically found in prairie remnants, railroad rights-of-way, roadsides, and other undisturbed sites. Plants grow 2 to 3 feet tall and produce pale pink to pinkish purple flowers from late June to early August. Leaves are 1½ to 3 inches wide and 4 to 6 inches long. After flowering, 2 to 4 inch long seed pods develop. Leaves and stems exude a milky sap when cut or bruised. Prairie milkweed is also known as smooth milkweed and Sullivant's milkweed. The plant is named after 19th century American botanist William Starling Sullivant.
Prairie milkweed adapts to a wide range of soils. It performs best in moist, well-drained soils in full sun. Remove the seed pods before they split open to prevent the spread of the plant in the landscape.
Butterfly, swamp, and prairie milkweeds can be establishing by planting seeds, bare-root plants, or container grown plants.
Milkweeds are fairly easy to grow from seeds, but seedlings are rather slow-growing and may take 2 to 3 years to flower. Sow milkweed seeds outdoors in fall. Lightly work up the soil, scatter the seeds over the prepared area, and then cover the seeds with approximately 1/4 inch of soil. The cold, moist conditions during winter break the seed's dormancy, allowing the seeds to germinate in spring.
Plant bare-root plants in early spring as soon as the ground is workable. Dig a hole and then place the dormant plant in the hole. The crown of the plant should be positioned ½ inch below the soil surface. Fill the hole with soil and gently firm the soil with your hands.
Plant potted milkweeds in spring after the danger of frost is past. Potted plants should be planted at the same depth as they were growing in their containers.
When planting milkweeds, choose your site carefully. Established plants are difficult to transplant.