Milkweed: Native vs. Tropical
Being bird-friendly and being insect-friendly go hand-in-hand. Of the insects, pollinators are a popular and important group for gardeners to focus on supporting. Houston is an important location not only for migratory birds, but also for a popular (and imperiled) migratory insect – the Monarch Butterfly. Because of this, local pollinator gardens and native plantings typically use milkweeds, the host plant family for Monarchs, as a central component to their effort.
Choosing milkweed plants proves to be much more difficult than many initially expect. The most prevalent milkweed species at nurseries around Houston is Tropical milkweed (Asclepias curassavica). Tropical milkweed is a large, showy milkweed with lovely yellow and orange flowers. It is hardy, easy-to-grow and supports Monarchs. Using this species in the Houston area, however, has its downfalls. First, Tropical milkweed is so hardy it doesn’t readily die-back in the winter. This may signal the normally-migratory butterflies that they’ve reached their destination or that they don’t need to continue the trip down the Mexico for the winter. If Houston does suffer a hard-freeze, those remaining monarchs and their caterpillars won’t survive the winter. The other issue with Tropical milkweed is its propensity to carry Ophryocytis elektroscirrha (commonly referred to as OE), a parasite whose primary host is the monarch butterfly. If the milkweed doesn’t die-back in the winter, the concentration of OE can build up to high levels.
Most Monarch specialists agree, when given the opportunity, planting native milkweeds is always a better option. Native milkweeds to Houston include Green milkweed (Asclepias virdis), Aquatic milkweed (Asclepias perennis), Slim milkweed (Asclepias linearis), Whorled milkweed (Asclepias verticillata), and Zizotes milkweed (Asclepias oenotheroides). These species can be difficult to find in local nurseries (though Houston Audubon’s Natives Nursery regularly has all five in stock). If you have tropical milkweed planted or if tropical is the only milkweed you can locate, don’t fret! To avoid the build-up of OE and to promote the continued migration of Monarch Butterflies you only need to cut that Tropical milkweed back. By cutting this species of milkweed back to less than 6-inches at the end of the season (and maybe once more during winter), you are helping keep OE at bay and assisting the monarch population. A good rule of thumb is to cut back your Tropical milkweed around Thanksgiving and then once more during the winter season.
Some Native Milkweeds