Milkweed: The Good, The Bad and The Ugly
Swamp milkweed (Asclepias incarnata)
Milkweed (Asclepias spp.) is a group of herbaceous ornamentals that are noted for their importance in the lives of the monarch butterfly (Danaus plexippus). Much has been written about the decline of the monarchs and the drive to preserve them. However, not all milkweed plants are equal and some can cause homeowners to regret planting them if they are not managed properly.
Researchers estimate that the monarch populations have declined by 80 percent since the 1990s. Monarch butterflies lay their eggs on milkweed plants, as monarch caterpillars will only eat milkweed to survive. Loss of milkweed habitat due to increased use of pesticides has been a significant contributor to the population decrease. Therefore, it would behoove all citizens to plant some milkweed to mitigate this problem. However, a wise choice will eliminate headaches down the road.
The first caveat is to be aware that milkweed contains cardiac glycosides which are toxic to animals, including horses, sheep, and cattle specifically. Dogs, cats, and humans can also be affected, but on a lesser scale since they are less likely to eat the plant. However, care should be taken that children and pets are closely observed when around the plants. In addition, make sure it is not planted near a fence line or pasture area. The milky sap can also be irritating to the skin; washing with soapy water immediately after exposure will remedy the problem.
Common milkweed (Asclepias syriaca) grows 2-6 feet tall and is found in fields, meadows, and along roadsides. The distinctive pink to lavender blooms appear from June to August and segue to the warty looking seed pods filled with the easily recognized fluffy down. This is a very aggressive plant that spreads not only by the airborne seeds, but also by underground rhizomes. One plant quickly multiplies to dozens and it takes time and energy to keep it under control.
A much less labor-intensive plant is Butterfly milkweed (Asclepias tuberosa). Still a native milkweed plant, it does not have the milky sap, does not have the aggressive growth habit, and is toxic only if eaten in large quantities. This 1-2 foot plant has bright orange flowers (although there are less common red and yellow cultivars) that appear in late spring through summer. The plants die back in the fall and are best left until spring before cutting back. They will self-seed, so keep it in check by simply remove the seed pods.
Beware of inadvertently purchasing a Butterfly bush (Buddleja davidii) at a big box store. This is NOT a milkweed plant is, in fact, an invasive species that should be avoided.
Swamp milkweed (Asclepias incarnata) is a smaller version (3-4 feet) of common milkweed with less milky sap. As the name implies, it thrives in moist conditions and is surprisingly tolerant of nearly all other conditions except drought. Prairie milkweed (Asclepias sullivantii) is also smaller (2-3 feet) and less aggressive than common milkweed. To help control the spread of these plants, pluck off the seed heads in the fall.
Whorled milkweed (Asclepias verticillate) is unique with white blooms from July to September. The narrow leaves are whorled around the 1-3 foot stem, thus the name. While beautiful, this species is particularly toxic to animals, so take care where it is planted.
Making wise choices when planting milkweed will aide monarch recovery, while keeping gardeners happy and safe.
Carol Shirk
Certified Master Gardener