Because of its intimate ties with that royal heart-stopper, the Monarch butterfly (Danaus gillipus plexipus), Milkweed (Asclepias sp.) is rather famous in the native plant world. Sixteen species of this diverse plant are found to Tennessee, including the three species that host the Monarch – Common milkweed (Asclepias syriaca), Swamp milkweed (Asclepias incarnata), and Butterfly weed (Asclepias tuberosa).
Host plants are important for butterfly gardeners to understand. Each butterfly species has a different plant or set of plants upon which it can lay its eggs. Once the precisely placed eggs hatch, the larvae (caterpillars) have immediate access to the food they need- which is a lot! Caterpillars are eating machines, increasing their body mass by 1000x before they enter chrysalis (their “cocoon” stage). Each butterfly-host plant relationship is unique and highly evolved. For example, Monarch caterpillars are safe from bird predators because milkweed contains toxic glycosides, making them nasty and deadly to eat. Other butterflies, like the Viceroy (Limenitis archippus) and Giant Swallowtail (Papilio cresphontes), resemble bird poop in the caterpillar stage to evade a fate as bird breakfast.
Butterflies not only require host plants for hungry caterpillars, but they also need nectar plants as hungry adults. If your garden space has the right host and nectar plants for your favorite butterflies, you can be sure to have sustained populations year after year. Monarchs can nectar on a wide variety of plants, including their host milkweeds, Echinacea (Echinaceae sp.), Lanceleaf coreopsis (Coreopsis lanceolata), Oxeye Daisy (Leucantheum vulgare), and Cardinal Flower (Lobelia cardinalis) among others.
If you look close enough, you’ll see that milkweeds serve a much greater purpose than just hosting butterflies. A whole community of arthropods (fancy word for insects) utilize this plant. We’ll use the example of Common Milkweed. You’ll often see Oleander Aphids (Aphis nerii) along the stem. These little orange blobs are the main ingredient in the tasty dish aptly named honey dew– gourmet food for ants. Ants “farm” aphids to get their fix on this nourishing aphid porridge. Ants are valuable creatures. Apart from being delicate members of the insect food web, they aerate soil, provide food for beneficial bugs, and take part in decomposition.
The big-bodied Bumble Bee (Bombus pennsylvanicus) might be the best friend of milkweed when it comes to pollination. When these bees mount a milkweed flower-head, they precisely place their hind legs right into the plant’s pollinia. Pollinia are pollen sacs linked by thin filaments. Only a nimble yet powerful insect can both penetrate the pollen sacs and also escape this complex structure. The pollen sticks to the hind legs of the bee, who in turn carries it to another milkweed in its search for more food. Voila, successful pollination!
Asclepias spp., Apocynaceae
Apart from insects, many birds make use of this multi-use plant. The downy fluff of their seeds is the equivalent of luxury linen. This provides an essential layer of warmth for the nests of late season birds like Gold Finches (Spinus tristis) and species that have several hatchings throughout the season, like Cardinals (Cardinalis cardinalis). Yellow Warblers (Dendroica petechia) and Northern Orioles (Icterus galbula) use the strong fibers found in milkweed stems to fortify their nests as well.
Choose the milkweed that fits your yarden conditions. All 3 species listed are perennial, which means they return year after year. If you have an open field with lots of space, you should let them self-sow freely! Common milkweed grows plentifully in Percy Warner Park along the road to the Nature Center. In late summer, you can see the wind-pollinated seeds floating gracefully in the breeze. The pods are large, ellipse-shaped, and filled with many eager seeds.
To get your personal plot of milkweed established, sprinkle the seeds around your area of interest in the fall after the last killing frost. They will lie dormant through the winter and then germinate the first of spring. This is a common life cycle of many native perennials, and the process is called “overwintering” or “cold stratification” if you are talking to a gardener. The hardest part here is remember where you planted them and to recognize the seedlings when they emerge. As wind-pollinated plants, you will certainly get some plants popping up outside your designated milkweed area. If so, they are easily transplanted. If you forget to plant your seeds in the fall, it’s fun and empowering to do your own cold-stratification. Take your seeds, wrap them in a moist paper towel and put in a plastic bag. Keep them refrigerated for 30 days, but keep an eye on them- they might germinate sooner. Once this happens, you can plant them directly outside at the start of spring.
Milkweeds are part of an intricate web of ecological interactions, from insects to birds to plant-appreciating people. Start your perennial patch today!