Milkweeds—Easing the Plight of the Monarch Butterfly

On high mountain trails in Michoacan, Mexico, I walked through forests of pine and fir, stopping to admire blossoms of purple senecio and red thistle, or to listen to the cheerful buzz of a hummingbird near a stream. I was happily immersed in my surroundings, but I knew that the real prize lay ahead. Our group rounded a bend in the trail, and there it was—a grove of oyamel fir trees, their boughs weighed down by huge clusters of resting Monarch butterflies.

Suddenly the sun's rays illuminated a branch, warming the butterflies to flight. The air quickly became thick with a flutter of orange wings, creating a sound like wind blowing through the trees. Butterflies were everywhere, sometimes landing on a hat or colorful shirt, or tickling a forearm. After a few moments, they dispersed, only to become active again as the sun reached another cluster. For the few incomparable hours that we shared the Monarchs' environment, we were all overwhelmed by being in the midst of one of the world's greatest natural phenomena.

Every fall, millions of Monarchs from the eastern United States and Canada migrate to about a dozen over-wintering sites high in the neo-volcanic mountains of central Mexico. (Monarchs on the other side of the Continental Divide spend their winters in the eucalyptus, Monterey pine, and cypress groves of California.) Although Mexican farmers in the area have long known about the huge winter aggregations, the sites remained a mystery to scientists until the mid-1970s.

In spring, the Monarchs return—mating, breeding, and feeding all along the migratory route. The butterflies that reach as far north as Canada are often up to four generations removed from those that left Mexico. But their epic journey is being threatened. Modern agriculture has made much of the U.S. farm belt inhospitable to Monarchs. In the East, industrial, commercial, and residential land use is gradually effacing the habitat that supports them.

This is where gardeners come in. We can make a big difference by growing the plants that are most important to the lifecycle of the Monarchs—milkweeds.

Milkweed Magnetism

The Monarch is unquestionably the most recognized and beloved butterfly in North America. It belongs to the subfamily of tropical milkweed butterflies, which are named after their host plant, the milkweeds (Asclepias species). Scientists believe that, originally, the Monarch followed milkweeds as they spread northward after the Ice Age. Unlike the plant, however, the butterfly can't survive cold winters and must return south to wait out the cold months.

Over a hundred species of milkweed are native to North America, and many are spectacular candidates for any garden (see "Milkweeds for the Garden"). They range from the tropical bloodflower (Asclepias curassavica), to the moisture-loving swamp milkweed (A. incarnata), to the now-scarce prairie milkweed (A. sullivantii). Milkweeds certainly are a must for every butterfly garden. Their leaves provide a home for Monarch eggs and a feast for Monarch caterpillars. Even better, hordes of adult Monarchs are drawn to their starburst flower clusters to sip nectar.

In nurseries, you're most likely to come across butterfly weed (A. tuberosa). It's showy, adaptable to poor soil, and well behaved. It won't take over your flowerbed like common milkweed (A. syriaca), which spreads aggressively by underground rhizomes. Butterfly weed's blossoms range from orange to red to yellow; 'Gay Butterflies' is a seed mix including all three colors.

Common milkweed may be a rambunctious grower, but many butterfly gardeners wouldn't be without it since it's the plant of choice for millions of Monarch caterpillars. The stout stem of the common milkweed grows up to six feet tall and is covered with fine hairs and wide, smooth leaves. In summer, it bears many large, fragrant, but somewhat dull purplish-pink flowerheads.

Until recently, the best way to get common milkweed seeds for your garden was to collect them from plants growing on the roadside. Nowadays, they are available from several nurseries (see Nursery Sources). Since seed-started plants can take up to three years to flower, however, you might want to ask a friend for a plant or get permission to remove milkweed from an area slated for development.

"The best way to propagate common milkweed is to find a main rhizome coming from the plant and work it out of the soil," says Minnesota Master Gardener Cathy Leece. "Aim for a one-foot piece with roots and above-ground growth."

Replant the rhizome at the same depth in sun or part shade; keep it watered and mulched; and trim back wilted growth. New sprouts should appear by late summer, growing into one or two plants the following year. Because of its tendency to spread, it's a good idea to keep common milkweed out of formal flowerbeds and in more natural areas of the garden. Should it become unruly, dig up rhizomes as they sprout new growth. Be persistent because they may be a foot or so underground.

For a more cultivated alternative to common milkweed that's almost as attractive to egg-laying Monarchs, Leece suggests swamp milkweed. Like most other milkweeds, it has fibrous roots and therefore won't take over your flowerbed. It's an enthusiastic self-seeder, so remove seedlings or share them with friends. These seedlings may bloom the following year, with attractive, long-lasting, pink flowerheads that have less of a "wild" look about them than those of the common milkweed. Be sure to plant swamp milkweed in a moist site.

All milkweed seeds, with the exception of the tropical bloodflower, should be stratified before planting: put them in a ventilated plastic bag or container of moistened sand or moss, and refrigerate for about four weeks. Milkweeds can also be propagated successfully from stem cuttings.

Summer and Fall Care

If you're already growing milkweeds, no doubt you've noticed their tendency to attract aphids-lots of them. Unsightly as they are, aphids don't harm the plant or the Monarch larvae. You can try blasting them with the hose or running your hand over the stalks. In time, aphid numbers will diminish due to natural pest/predator cycles.

Spider mites also can be controlled with water sprays or with insecticidal soap. If this doesn't work, make a spray containing small amounts of bleach and liquid dish soap in water. Remove larvae from the plant temporarily, spray the foliage, and then rinse with water within a few minutes. Avoid spraying any leaves with Monarch eggs, or rinse them off right after spraying.

Deadhead milkweed flowers to prolong blooming during summer. At the end of the season, allow the plants to form those attractive pods that look great in dried-flower arrangements. Silky, parachute-like seeds will begin to drift out of the mature pods in late fall. Gather a few pods and store them indoors until spring, then set the floss outside for nesting birds, such as hummingbirds and warblers.

Cut back old milkweed stalks in late winter, before new shoots begin to emerge. Leave the stalks in a conspicuous place so that orioles and other birds can strip fibers for nest material. Then watch for the new growth that will soon become a mass of heady blooms-your own personal patch of Monarch heaven.

A Fragile Phenomenon

Monarch expert Lincoln Brower calls his favorite butterflies "a hardy and fertile breed," able to rebuild populations after catastrophic weather episodes such as snowstorms. However, he's not optimistic about the future of the Monarch's yearly migration. Commercial logging is proceeding at a frightening pace in Mexico's oyamel fir forests, opening up the canopy, and altering the microclimate. North of the border, development is diminishing and fragmenting the habitat for migrating Monarchs.

Aside from growing milkweeds in our own yards, what can we gardeners do to help? Robert Michael Pyle, author of Chasing Monarchs: Migrating with the Butterflies of Passage (Houghton Mifflin, 1999) urges the following:

• Conserve or plant new stands of milkweed, and fight roadside spraying.
• Plant other nectar-rich flowers that bloom in fall, such as asters, sedum, and goldenrods, to provide much-needed energy for migrating monarchs.
• Support organizations like Monarch Watch and Monarch Program.
• Get involved in butterfly tagging and monitoring or some other volunteer activity.

Although Pyle and I both live in the Monarch-poor Northwest, he's invited me to join him for fall tagging in eastern Washington. I'm hooked, so I can't wait!

Organizations:

Nursery Sources: