The white woodland milkweed (Asclepias exaltata), the swamp milkweed (A. incarnata) and the common butterfly weed (A. tuberosa) are all first-class plants for the Southern garden. The genus commemorates Asklepios, the Greek god of medicine, and many members of this plant group have a long history of use in chest complaints, supposedly acting specifically on the lungs.
The often-fragrant milkweed flowers are quite sophisticated in the way they spread pollen. When an insect alights, they find the flower’s surface slippery and claw about for a foothold. As they struggle, one or more of the sharp projections on their feet will catch in little clefts at the flower’s base. Soon a foot is drawn into a slot at the end the cleft, where a little dark brown container holds masses of yellow pollen. As the visitor gives a final tug to free itself, the container goes along with the foot, firmly caught until the pollinator lands on another flower. There the container usually falls though another slot and fertilizes the flower. Sometimes, with smaller insects, it doesn’t work and they wind up trapped — without escape.
Woodland milkweeds flower in dappled sunlight to medium shade, their pendant white flowers (sometimes tinged with lavender or a pale green) blooming in clusters atop 3- to 5-foot-high plants resembling bursting fireworks without the blast. This species is commonly called the poke milkweed because of a very superficial resemblance to American pokeweed (Phytolacca Americana), but only a person who’s been walking malls for 20 years would make that comparison. After fertilization, the fading flowers produce 6- to 10-inch vertical seed pods that last well into autumn. Both stems and leaves contain a milky sap. They need some shade and a good, moist — but not wet — woodland soil.
Swamp milkweeds grow between 4 and 5 feet tall; they bear long, opposite, smooth lance-shaped leaves. The plants bloom in midsummer, with many quarter-inch, deep-pink flowers opening in small clusters about 2 inches wide. The eventual pods are from 2-4 inches long. Swamp milkweeds are perfect for the wild garden, meadow garden and the back of the border. They prefer moist, open areas, especially close to water.
Butterfly weed has more common names than the rest, including swallow-wort (wort is an old English word for plant), chigger-flower, wind root and pleurisy root. To my knowledge, it’s the only milkweed lacking milky sap.
The flowers are both colorful and complex in form, blooming in large flat umbels with colors ranging from bright yellow to reddish orange — but usually just plain orange. While few blossoms form mature fruits, there are usually one or two pods on any plant that eventually open to produce ranks of seeds, each with a powder-puff of silky threads, but much smaller than the pods of common milkweed.
Because of their deep-thrusting roots, butterfly weed should be moved only when young. Once it’s established, you can forget most care; in addition to its other qualities, this plant is extremely drought-resistant. If grown in good garden soil (especially when laced with compost), they tend to grow taller than wild types but should require staking only in damp summers, when there is a tendency to sprawl. All are hardy in our mountain gardens.
[Peter Loewer, aka The Wild Gardener, is a regular contributor to Xpress.]