Found throughout much of North America, common native milkweed is the larval food source for the monarch butterfly. Milkweed’s silky filaments were once used as stuffing for pillows, mattresses, and life preservers. Farmers stopped growing milkweed on a commercial scale and began using massive amount of pesticides and monarch butterfly numbers fell. Milkweed silk may get a rebirth in commercial farming for companies wanting thermal insulation, acoustic padding, and oil spill absorbers.
Milkweed forms umbrella shaped flowers, dispersing seeds into the wind on their silk filaments. Milkweed has simple, erect stem that can reach 1.5 to 6 feet in height and is pollinated by bees and insects. It has a thick, long rhizome that stores nutrients and produces new sprouts, providing ample food for a range of insects besides the monarch butterfly. The sap of milkweed contain cardiac glycosides that are mildly poisonous to humans, so kids need to wash their hands to remove any sap. A monarch butterfly caterpillar eats the milkweed leaves and collect toxins in its body. The toxins remain in the caterpillar body after its transformation into a butterfly and makes it distasteful to birds and other predators.
There are many varieties of milkweed. Local native milkweed varieties are the best for the monarch butterflies. However, the only species of milkweed widely available at nurseries in the United States is Asclepias curassavica, which is native to the tropics. This tropical milkweed hosts a protozoan parasite. As caterpillars, monarchs ingest the parasite along with their normal milkweed meals, and when they hatch from their chrysalises they are covered in spores.
Tropical milkweed does not die back in the winter like native milkweed does, and so monarchs are establishing winter-breeding colonies and not migrating, increasing the odds of monarchs becoming infected with the crippling parasite. Tropical milkweed must be cut back to 2 – 4 inches in height starting the end of October and pruned of all leaves during the winter. Cutting back the milkweed will also help to eliminate spores that may be present on the plant and discourage monarchs from establishing winter-breeding colonies.
Kids can grow native milkweed easily in a wide range of soils.The California Narrow Leaf Milkweed (Asclepias fascicularis), seen in the picture above, is a western native species of Milkweed with large white flowers and long, showy narrow leaves that is recommended for use in the West.