It’s one of the greatest migrations of the animal kingdom: Every spring, hundreds of thousands of monarch butterflies sweep across the continent from Mexico to Canada and then back again in fall, a journey spanning nearly 3,000 miles and multiple generations. In fact, recent studies show that it takes up to four generations for monarchs to make it north out of Mexico and into Southern Canada!
Along the way, the butterflies feed on a variety of nectar-rich flowers but breed on only type of plant: milkweed.
There are 140 species of milkweed, but only a quarter of them are known to be important host plants for monarchs and even less are available commercially for planting.
The Importance of Milkweed
When you think about it, it’s rather remarkable how a butterfly can spot a single milkweed from the sky. She lands on it, scratches it with her front legs, tastes it with her feet, and confirms that it’s indeed milkweed. She then proceeds to lay her egg on a leaf — and only on the leaf of a milkweed.
This is because monarch caterpillars depend on the plant for food, eating every leaf in their path until they complete their metamorphosis (a cycle that takes about four weeks). Unlike adult monarchs (butterflies), caterpillars cannot simply feed on any plant they please. And that might lead you to wonder: why milkweed?
Perhaps it’s by natural design: The chemical compounds in the plant make the caterpillars toxic to potential predators (such as birds), with the sap of certain species of milkweed being more toxic than others. The compounds, however, have no adverse effect on the caterpillars themselves. They spend up to two weeks eating, growing, and molting on the same milkweed plant before they pupate.
The striking appearance of the butterflies and caterpillars also serves as a warning to predators that they are toxic. Predators learn to associate the colors and patterns with a bad taste and generally avoid preying on monarchs altogether.
Unfortunately for the monarchs, milkweed populations have dwindled due to the use of herbicides in crop fields, where milkweed pops up abundantly between rows of corn and soybeans in the Midwest. It’s no accident that common milkweed is called as such because of its invasiveness as a weed! But loss of habitat is only one part of the problem — also to blame are climate change, drought, and disease, the culprits responsible for not only the decimation of milkweed, but also nectar sources for adult monarchs.
So, How Can We Save the Monarchs?
One important step is to plant a variety of nectar-rich flowers in the garden that bloom at different times. Showy annuals like zinnias and phlox are attractive to butterflies (as well as other pollinators like bees and hummingbirds). Growing a good variety of flowers helps sustain all the beneficial insects, adds beauty to your yard, and contributes to the overall health of the local ecosystem.
Equally important are perennials, especially native perennials like echinacea (coneflowers) and coreopsis, that can provide a constant and reliable source of food. For perennials that do double duty as food for butterflies and food for you, consider planting flowering herbs like sage and oregano.
Not All Milkweed is Created Equal
The next step, of course, is to plant milkweed in your garden. More importantly, try to plant native milkweed.
It’s been found that one of the most popular (and non-native) milkweed plants sold by nurseries, Asclepias curassavica or tropical milkweed, may actually do more harm than good. When grown in warm climates where the plants don’t die back, the year-round tropical milkweed encourages monarchs to overwinter in the Southern United States rather than continue their migration to Mexico. By hatching and feeding on tropical milkweed, caterpillars have an increased chance of being infected with a protozoan parasite called Ophryocystis elektroscirrha (OE), which weakens them as adults.
OE is found in all species of milkweed, but isn’t a problem with natives because the leaves are only desirable to caterpillars in the early stages of growth. Once the plant goes dormant in winter and loses its leaves, OE is no longer a threat. But with tropical milkweed, the leaves stay viable all winter long and make it more likely that a caterpillar will become infected.
A report by the Monarch Joint Venture found that 49 percent of winter-breeding monarchs had OE infections, compared to only 9 percent of migratory monarchs sampled in Mexico and 15 percent of migratory monarchs sampled in the northern U.S. and Canada.
This is not to say that gardeners in California and the coastal Southern states (or zones 8 through 11) who grow tropical milkweed should immediately rip it out — just remember to cut it back in late fall to reduce the spread of OE, promote new growth of fresh, healthy leaves, and encourage monarchs to finish their migration.
If you want to plant new milkweed, there are several species of native milkweed in the U.S. One of the most common, Asclepias tuberosa, is also known as butterflyweed. It’s native to most parts of the country (except the Northwest) and blooms in a brilliant orange or yellow. (Not to worry, Northwesterners: you can still plant showy milkweed, Asclepias speciosa, or Mexican whorled milkweed, Asclepias fascicularis.)
Butterflyweed does best in dry, sandy soil with little nutrition. It’s often seen growing in fields and along the sides of the road, which means it’s drought-tolerant and a good choice for low-maintenance perennial gardens.
I have a few species of milkweed in my backyard, including butterflyweed. Greenwood Nursery sent me some of their plants last year and I’ve found them to be impressively resilient, surviving not only a major heat spell, but also oleander aphids, milkweed bugs, and many, many cycles of hungry caterpillars. It takes only a few caterpillars to defoliate an entire plant in a couple of weeks, but sure enough, the milkweed comes back every time.
Here are a few growing tips from my own experience:
- Purchase plants from a reputable nursery to avoid systemic pesticide use that could harm pollinators, or start your plants from seed.
- Offer a couple varieties of milkweed, as some monarchs may have a preference for one or the other, and plant a few patches throughout your yard for them to land on.
- Be aware that common milkweed (Asclepias syriaca) can spread aggressively by runners. Plant it in a suitable place in your garden where it won’t invade your lawn or overcrowd other plants.
- Plant low-growing perennials in front of the milkweed, as they’ll hide the spindly “skeleton” stems once the monarchs finish feasting. You’ll still be able to see them bloom, as the caterpillars don’t eat all the way up to the flowers.
If you want to plant milkweed in your garden, Greenwood Nursery carries orange butterflyweed and Hello Yellow butterflyweed in 3-inch pots and 1-gallon pots. (Plants ordered in winter will arrive dormant.) They are big supporters of these beautiful monarchs and named the butterflyweed their 2017 Perennial Plant of the Year! As a family-owned nursery in Tennessee, Greenwood Nursery has been in business for four decades and I can see why — they are an absolute pleasure to deal with.
If you head to the front page of their site, you can sign up with your email address to receive 10 percent off your first order!
Cheryl, the owner of Greenwood Nursery, is also offering an exclusive coupon to Garden Betty readers for a free beautiful potted strawberry plant that will fruit this spring. Simply enter code “gardenbetty” at checkout to redeem. (Coupon expires April 15, 2017.)
If butterflyweed is not native where you are, or you want to diversify the milkweeds in your garden, I encourage you to visit a native plant nursery in your area. You can also source seeds from a local vendor on the Xerces Society’s Milkweed Seed Finder or online from Botanical Interests.
This post is brought to you by Greenwood Nursery. Thank you for supporting the sponsors that support Garden Betty.