Jane's Garden 8/31/14: Perennial Milkweed and Butterfly Milkweed

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More than 100 perennial Milkweed species in the Asclepias genus originated in the Americas. Similar African plants with inflated prickly seed pods were recently reclassified into the Physocarpus genus.


Acslepias was the mythical Greek god of healing. Parts of some milkweeds have been used in folk medicines. Milkweeds contain the chemical oleandrin, a cardiac glycoside. The sap is a milky, acrid latex containing alkaloids which may irritate the skin in some people. Monarch butterfly caterpillars ingest the toxins, making them distasteful to birds and other predators.

Nectar in Milkweed flowers attracts pollinators — bees, wasps, butterflies, moths and hummingbirds. Milkweed pollen is not a single grain or tetrad, but grouped in complex sacs called pollinia. The feet or mouthparts of pollinators become stuck in any of the 5 slits between the flower anthers. The pollinia thus mechanically attach to the pollinator. When the pollinator leaves, pairs of pollen sacs are pulled free and are carried to the anther slits of a different flower to ensure pollination.

On all Milkweeds, the characteristic small, five-petal flowers reflex downward surrounding a central waxy corona. The Australian/Asian Hoya plants have similar flowers.

Tropical Milkweed, Asclepias curassavica, from South America, zones 9-12, is commonly called Bloodflower. It is readily available in local nursery outlets. This perennial has deep tuberous roots and grows, about 3 feet tall and is evergreen in South Florida. It dies to the ground in central Florida’s cooler winters. Loose clusters of a few flowers are usually red and orange, although there is a yellow, weaker selected variety.

There are at least 20 species of Asclepias native to Florida, but few are commercially available. The most widespread Milkweed in the United States is A. tuberosa commonly named Butterfly Milkweed, which grows in zones 4-10. It grows naturally in about 40 lower states but not in the Pacific Northwest or the Canadian maritime provinces. Its northern limit is about latitude 48.

The plant grows 2 to 3 feet tall from a deep, underground rhizome. It is prevalent in dry sandhills, woodland edges, roadsides and any well-drained, full-sun site. It does not tolerate root disturbance, wet soils or excessive irrigation.

Large clusters of bright orange flowers top sturdy stems that range from 6 to 12 inches high in younger plants to 36-inch stems in an older specimen.

This long-lived perennial is the host plant for Monarch Butterfly caterpillars. Adult Monarch females lay eggs the size of a pinhead on the alternate, lance-shaped leaves. Tiny caterpillars hatch after three or four days and munch the milkweed leaves for about two weeks before going into a chrysalis, where they change into adults.

Milkweed seedpods are elongated, paper-thin pods called follicles. When mature, they dry and split open to reveal rows of overlapping black seeds attached to silky floss called pappus. The seeds are wafted away on the filament-like parachutes to germinate and grow far from the parent plant.

The second most common Milkweed is A. syriaca, growing naturally in about 39 states and six provinces, but not in Florida, the southwestern states, or Idaho and Washington. Flowers are clustered in a round globe atop 3-foot tall stems. Heat zone 10 in Florida is too hot for this species to survive.

Milkweed is a colorful and useful plant in wildflower meadows and butterfly gardens throughout Florida. Companion plants include Black-eyed Susan, Rudbeckia; Purple Coneflower, Echinacea; Blazingstar, Liatris; and the evergreen flowering vines Carolina jessamine, Gelsemium sempervirens and Coral Honeysuckle, Lonicera sempervirens.

Jane Weber is a professional gardener and consultant. Semi-retired, she grows thousands of native plants. Visitors are welcome to her Dunnellon, Marion County, garden. For an appointment, call 352-249-6899 or contact JWeber12385@gmail.com.