American butterfly lovers were not surprised at last week’s announcement by the International Union for Conservation of Nature that the monarch butterfly is now considered an endangered species. Where I live, monarchs were once common butterflies of summer, but not anymore. Monarch populations are estimated to have dropped 80 percent, with most of the blame placed on habitat destruction and climate change.
In addition to their large size and striking orange and black colours, monarch butterflies (Danaus plexippus) are famous for their 3,000 mile twice yearly migration between central Mexico and the northern US. Reproducing as they go, always on milkweed plants, three generations of monarchs carry through the mission, each one somehow knowing what it is supposed to do.
The good news is that gardeners can help by hosting or even rearing monarchs. If you live in their breeding territory, adding milkweeds to your garden ensures that monarchs have appropriate nursery plants for their young. If you live along one of the monarch’s southward migratory routes, you can grow a nectar-rich flower garden comprised of late-blooming plants monarchs like, called a Monarch Waystation. It’s a special place where migrating monarchs can stop to tank up on nectar and rest for the night.
Gardening with Milkweed Plants
Of the nine milkweed species native to North America, monarchs prefer common milkweed (Asclepias syriaca), swamp milkweed (A. incarnata) and butterfly weed (A. tuberosa). Of the three, butterfly weed is the best choice for a flower garden because it grows into a compact mound, requires no special soil, and is willing to bake in full sun. Swamp milkweed needs a moist soil with partial afternoon shade, but it is a lovely perennial when these needs are met. Common milkweed is a vigorous spreader that is most at home in a meadow situation. When growing common milkweed with other flowers, be prepared to see it pop up in unexpected places, because the roots of common milkweed do not know the meaning of staying put.
All milkweed plants, but especially common milkweed, respond to being cut back by developing a flush of fresh foliage in late summer. A large citizen science research project sponsored by the University of Michigan called Regrow Milkweed for Monarchs is studying the benefits of pruning back common milkweed by July 20. Scientists already know that late season monarchs lay more eggs on milkweed regrowth, and that the larvae tend to be bigger and healthier than those that feed on older leaves.
Should you have milkweed with larvae that disappear as soon as they hatch, cover the plants loosely with horticultural fleece or wedding net to exclude predators. When the caterpillars are ready, they will crawl away to find a place to pupate.
Grow a Monarch Waystation
Hosted by the University of Kansas, the Monarch Waystation program now lists almost 50,000 registered gardens developed to support monarchs. Many are community or school gardens, because the requirements are modest: a milkweed accompanied by annuals and perennials that monarchs like, for example Mexican sunflower (Tithonia), zinnias, and native goldenrods and asters. The plants need not be grouped together in the same place, but should occupy at least 100 square feet in total space.
I’ve been watching monarchs for many years, so my place is geared toward providing milkweed for any monarchs that care to drop a few eggs, but more importantly, to service the southward migrants that pass through in late September and early October. I wait for the autumn migration like others anticipate their favourite sporting event, and my Waystation plantings have spread into every corner of the yard. Goldenrods, native asters and butterfly bushes are anchor plants, but the monarch favourites year after year are Mexican sunflowers (Tithonia) and zinnia, both native to Mexico. Perhaps the nectar gives them a taste of their other home.
Many gardeners are helping monarchs by rescuing baby caterpillars before predators can get them, or larger ones feeding on failing plants, and rearing them in net cages for safe release. Having done it, I can report that rearing monarchs is labour-intensive but rewarding work. You must feed the hungry larvae fresh milkweed leaves daily two weeks, and then provide a safe place for them to pupate for another two weeks. But when you finally watch the miracle of a beautiful monarch emerging from its chrysalis and spreading its wings, every moment of effort seems worthwhile.