Feed the Caterpillars! Why I'm Growing Milkweed, and You Should Too.

Last summer as an experiment, I bought three milkweed plants from the Morton Arboretum’s plant sale. About a month after we put the young plants in the ground, the kids and I spotted our first striped monarch caterpillar on one of the leaves. Clearly, the butterflies found the plants a welcome addition to the back yard.

This year, I’m planning to strip the sod off the low spot in the back yard that always floods, near the sidewalk, and plant water-loving natives, including more milkweeds. Milkweed (Asclepias) is the only source of food for monarch butterfly caterpillars. Douglas Tallamy, in his excellent book, Bringing Nature Home, notes that many insect caterpillars can eat only one type of plant. Consequently, monarch caterpillars eat only milkweeds—not lawn, hostas, or lilacs.

If we don’t plant milkweed, monarch butterflies cannot produce more monarch butterflies. And at least 11 other types of butterflies need milkweed plants.

Monarch Watch says that monarch butterflies are threatened by humans’ destruction of their habitats. Roads, shopping malls, and suburban housing all have destroyed areas that monarch butterflies need to feed their young and reproduce. Because some people consider milkweed to be a noxious weed, much of the butterflies’ food source has been destroyed. According to the Save the Prairie Society, today less than 1/100 of 1% (0.01%) of Illinois’ original prairies, which covered most of the state, remains. The landscape of Elmhurst, IL, where I garden, probably once looked much like the Wolf Road Prairie.

The Illinois Wildflowers web site lists three different milkweeds that are native to Northeastern Illinois and its original prairies and may be suitable for home gardens. Several milkweeds are on the Wolf Road Prairie’s plant list. I’m listing both Latin and common names here, because plants are often sold at specialty nurseries by Latin name. I encourage you to click on the links to view photos of these beautiful plants, which I can’t publish here without permission.

Prairie Milkweed (Asclepias sullivantii), also known as Sullivant’s Milkweed, grows 2 ½ to 3 feet tall and has broad leaves. The plant produces pink flowers in mid-summer. It requires full sun and moist soil conditions, making it a good choice for that wet spot in my backyard.

Butterfly Milkweed (Asclepias tuberosa interior) grows 1 ½ to 3 feet tall and resembles a small bush. The 2- to 4-inch flowers appear in midsummer, and the plant produces 4-inch seed pods. The long-lasting and colorful flowers make this a showy plant. The plant needs full sun, and well-drained soil. I bought this plant at the Morton Arboretum’s plant sale last year.

Whorled Milkweed (Asclepias verticillata) requires full sun and dry soil. The plant, 2 to 3 feet tall, is unbranched and has 2- to 3-inch clusters of white flowers. It originally ranged through most of Illinois, except the far south part of the state.

Purple Milkweed (Asclepias purpurascens) is an unbranched plant about 2 to 3 feet tall that I bought last year at the Morton Arboretum plant sale. Leaves, as for other milkweeds, are dramatic: 6 inches long and 3 inches wide. The plant does well in well-drained soil and full sun to light shade.

Swamp Milkweed (Asclepias incarnate) grows well in moist to damp soils and full sun to part shade. It is a good plant for a spot that floods regularly. It grows 3 to 5 feet tall and produces clusters of pink, white, or light purple flowers. The plant’s roots are specialized for growth in wet soils.

Common Milkweed (Asclepias syriaca) may be too invasive for many home gardens.

Because these plants are unlikely to be available at the local Home Depot any time soon, gardeners must rely on other sources to obtain them. Online nurseries, such as Wisconsin’s Prairie Nursery and Minnesota’s Prairie Moon Nursery are mail-order sources but may not carry local genotypes—plants reproduced from stock originally growing in Illinois prairies. The Natural Garden, Inc., a local nursery in St. Charles, sells several types of milkweed—Swamp Milkweed, Common Milkweed, and Whorled Milkweed.