Some of them are shrubs, some grow in wet soil, and others thrive in dry scrub. They grow in South Africa and there is at least one milkweed in every state of the U.S.
Their flowers vary but all have seedpods filled with a fluffy, silky substance that carries the seeds on the air.
Asclepias flowers attract several types of butterflies and their leaves provide food for Monarch butterfly caterpillars.
There are three potential problems with growing Asclepias: The milky sap can cause a rash on sensitive skin, they attract aphids and cows can become sick if they eat it.
Many Asclepias are native to Oklahoma but you can also grow other varieties with special care.
The USDA Plants Database lists them at http://plants.usda.gov/. If you have a milkweed to identify, go to http://shrvl.com/n751D to see 226 photos and drawings of Asclepias varieties.
Choose one of these garden-worthy Asclepias species for your garden.
Butterfly weed, or Butterfly flower, Silkweed, Silky Swallowort, Indian Posey, Orange Root or Virginia Silkweed, (Asclepias tuberosa) likes dry soil. Grows up to 3-feet tall with red, orange and yellow flowers. They are native to most of the U.S.
Asclepias tuberosa is the milkweed most commonly sold by nurseries. It does not spread wildly but still has all the benefits of attracting butterflies.
In “Oklahoma Gardener’s Guide” Steve Dobbs wrote about Asclepias tuberosa, saying that you can’t beat its resilience for growing in poor, dry spots. Gay Butterflies Mix is a combination of orange-red, pink and yellow flowers.
Oklahoma native Antelope-horn milkweed is also called Spider milkweed, Antelope horns, Green-flowered milkweed, and Spider antelope-horns. Asclepias asperula or Asclepias viridis has a round ball shaped cluster of flowers.
Bloodflower – also called Indian Root and Swallow-wort (Asclepias curassavica) is perennial in South America and is grown as an annual here. It typically has red or orange-red flowers; the variety Silky Gold has yellow flowers and grows to 3-feet tall.
Perennial Narrowleaf milkweed (Asclepias fascicularis) grows to 3-feet tall in dry soil. Pink flowers.
Swamp milkweed (Asclepias incarnata), an Oklahoma native, grows to 4-feet tall with pink flowers. One hybrid, Ice Ballet has white flowers. Likes moist soil.
Showy milkweed (Asclepias speciosa) has purple-pink flowers but likes well-drained soil. Plants for a Future database (www.pfaf.org) says the plant’s flowerbuds taste like peas when cooked. This one can become invasive if allowed to seed at will.
Prairie milkweed or smooth milkweed, Asclepias sullivantii, has pink-burgundy flowers on 2-foot tall stems in moist soil. This one is an Oklahoma native that is threatened because its numbers are so low. The seedpods are collected and used in dried flower arrangements.
Common milkweed, A. syriaca, is a native in more than half of the U.S. They grow to 5-feet tall with fragrant lavender flowers. Can become a weed in good soil.
Whorled milkweed (A. verticillata) has threadlike leaves and white flowers.
Dobbs recommends taking tip cuttings to root at the end of the summer. Keep the plants going indoors over the winter and plant them next spring.
Deadheading can prolong the flowering season. Remove flowers as they fade so the plant will continue to produce more buds.
Gardeners often allow a few seed pods to form. In the spring put the floss and seeds outside. The birds will use the floss for their nests and the seeds will sprout to make plants.
Useful resources for native plants can be found at http://www.missouriplants.com/, http://www.kswildflower.org/, and Oklahoma Native Plant Society at www.usao.edu/~onps/.