Green Thumb – Growing Milkweed for Monarch Butterflies

Posted: August 14, 2020

Whenever I see milkweed growing along the side of a road, I wonder if I’ll see Monarch butterflies. They lay their eggs on milkweed because it’s the only source of food for their caterpillars.

Monarch Caterpillar

Two years ago a patch of Common Milkweed showed up in my yard, and Monarch butterflies soon found it. I collected two caterpillars because I wanted to observe their life cycle. They transformed through their stages and climbed out of the jars as beautiful butterflies. Unfortunately, the milkweed also attracted aphids, which attracted ants, which resulted in a heavy coating of unsightly black sooty mold on all the leaves.

The next spring I made an important discovery. Common Milkweed spreads. If you try to pull it out and leave behind a small piece, you’ll find it popping up many feet away. It has sneaky horizontal roots and seeds. I now had a lot more milkweed.

I had no plans to raise caterpillars the next year, just let the milkweed grow and check on things from time to time. As the plants grew taller, Monarch butterflies showed up and soon there were tiny caterpillars.

Early in the summer I was surprised to hear some people say they were already releasing adult butterflies.  My plants had only small caterpillars and two tiny green frogs high up on one of the plants. The frogs looked too small to be a problem. I also noticed there were no aphids or ants, so I decided to leave nature alone.

Monarch Chrysalis

By late summer there were so many small Monarch caterpillars that the milkweed plants looked ragged. Yet, there were few medium or large caterpillars. That’s when I saw the fat, green frog with a contented smile.

This situation called for emergency intervention. The caterpillars I rescued were little eating machines that needed lots of fresh milkweed.  Before long, they turned into green chrysalis “ornaments”, safe and sound on my screened porch.

Monarch Life Cycle

Most of us were taught that toxins in milkweed protect Monarchs from predators, but some predators have adapted. Wasps are some of the worst. Then there are ants that feed on both eggs and caterpillars, and spiders that feed on small caterpillars at night. I have my own suspicions about little green frogs.

Emerging Monarch

During their migration north from Mexico, Monarch butterflies go through several generations as they follow the advancing season. But then, as the days get shorter and cooler, something miraculous happens. In the last generation there are butterflies that can live up to eight times longer than their parents.  They fly south to Mexico and do not reproduce until spring.

Making the effort to rescue Monarch caterpillars saves individual butterflies, but greater benefit comes from creating a habitat they like. The Monarch Waystation program encourages individuals and groups to plant milkweeds and various flowers for the Monarchs to produce their summer generations and prepare them for their fall migration. You can create one in your own yard and have it certified as an official Monarch Waystation by Monarch Watch. For more information see https://www.monarchwatch.org/waystations/.

Types of Milkweed

In Northern Illinois there are several types of milkweed you can grow in addition to Common Milkweed. Their leaves are a food source for Monarch caterpillars and their flowers provide nectar for the adults. Swamp Milkweed is a well-behaved wetland plant. Once established, it can grow up to 5 feet tall in medium moist conditions. Whorled Milkweed grows to 18 inches tall and is a bit invasive, but very suitable for a dry, sunny site. Poke Milkweed grows up to 5 feet in sun to part shade. Butterfly Weed, a member of the milkweed family, attracts many types of butterflies. It grows 12 to 36 inches in clay and dry soil. It has pleasing orange, yellow or red flowers all summer.

Six of the Monarch caterpillars I rescued that day turned into beautiful butterflies. When they took off, they flew high up in the air to continue their amazing journey. By mid-September I had raised and released 27 Monarch butterflies.

Janice M. Weber – University of Illinois Extension, DeKalb County Master Gardener


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