Butterfly gardens are a popular theme in gardening, and the main butterfly many gardeners want to attract is the king of the butterfly world — the monarch. Monarch butterflies are among the largest and showiest of butterflies in North America. If you want to attract them to your garden, you must have some milkweed plants. Milkweeds, plants in the Asclepias genus, are the host plants for the monarch butterfly. The monarch will only lay eggs on milkweed; it is the only food source the larvae eat. Without milkweeds, there would be no monarch butterflies.
Asclepias contain a variety of chemical compounds, including a cardiac poison that is poisonous to most animals with backbones but which doesn’t hurt the monarch caterpillar. These compounds, when ingested by the feeding caterpillars, make monarch caterpillars and adult butterflies poisonous to potential predators.
Insects change in form as they grow, a process known as metamorphosis. Butterflies undergo complete metamorphosis, in which there are four distinct stages. The four stages are the eggs, larvae (caterpillar), pupa (chrysalis) and adult. Adult monarchs look for a milkweed plant on which to lay their eggs. On average it takes four days for the eggs to hatch and the larvae to emerge. The larva, or baby caterpillar, does nothing but eat milkweed for the next couple of weeks. Once the caterpillar is fully grown, it begins to look for a place to attach itself so that it can start the process of forming a chrysalis. The caterpillar attaches itself to a stem by spinning a silk mat from which they hang upside down and transform into a chrysalis. The chrysalis phase is a time of rapid change. The body parts of the caterpillar are undergoing a remarkable transformation, to become the beautiful adult butterfly that emerges.
Once a monarch emerges, its primary job is to reproduce — to mate and lay the eggs that will become the next generation. Monarchs usually mate when they are three to eight days old. Females begin laying eggs immediately after their first mating, and both sexes can mate several times during their lives. Adults in summer generations live from two to five weeks. This first-generation monarch butterfly will die after laying eggs for generation number two. An interesting fact is the last generation of monarchs does not lay eggs immediately. Instead it migrates south to Mexico, where it lives for six to eight months (in comparison to two to six weeks of those in the previous three generations) — making them some of the longest-lived of all butterflies. These migratory monarchs return next season to begin the cycle all over again. Through monarch tagging programs we have learned that many of these butterflies return to the exact same place as their ancestors for many generations.
During the breeding season, monarchs require milkweed plants upon which to rear their larvae and nectar sources to sustain the adults during reproduction. Nectar sources are also required by the butterflies to fuel the fall migration to Mexico, as well as the spring flights northward.
To ensure there are food and nectar sources for monarchs, plant a diverse mix of milkweed plants, and other nectar plants as well. There are over 100 species of milkweeds in North America, with only 30 species of much interest to monarchs, since many of the others are rare or confined to remote areas of the county. There are over 10 species of Asclepias that are native to Arkansas, with flower color ranging from pink, purple, white and green to bright orange or yellow. While most gardeners are familiar with the orange butterfly weed, Asclepias tuberosa, there are several others that are readily available and would add to your gardens. The common milkweed, A. syriaca, grows two to three feet tall and has fragrant, pinkish-purple blooms that bloom from late spring through summer. Swamp milkweed, A. incarnata, forms a strong taproot with beautiful pink flowers. While it is found in moist, boggy areas in the wild, it does well in average garden soil with supplemental watering. One of the earliest and more compact blooming milkweeds is the green milkweed, A. viridis, with green blooms from May through June. One of the longest blooming milkweeds is the whorled milkweed, A. verticillata, blooming up into September with clusters of small white blooms.
Most gardeners still put the A. tuberosa, or butterfly weed, as their top choice for milkweeds in the garden and consider it the showiest. The bright orange or yellow blooms make it a show stopper. It, too, has a strong taproot, which makes it difficult to transplant. Plant it and let it stay there.
Almost all milkweeds can be easily grown from seed. The warty or canoe-shaped seed pods on most plants will split open when ripe, releasing numerous silky-tailed seeds. Fall is the ideal time for planting seeds, but plants may be planted spring through summer. Most do best in full sun, but some will tolerate light shade.
Janet B. Carson is an extension horticulture specialist for the University of Arkansas Cooperative Extension Service.