Milkweeds and their Importance to Monarchs


This week I made my monthly trip to Bexley to work in the Heritage Garden at the Ohio Governor’s Residence in Bexley, Ohio. Before we set out to plant, weed, and prune, the Governor’s Gardeners have some educational time learning about plants in the Heritage Garden. That day we headed out for the large patch of Common Milkweed that was in full bloom and full of bumblebees. This was a great way to celebrate Pollinator Week as we learned that this stand of milkweed is one individual plant that has colonized that patch of the garden!

I then headed to the Prairie part of the Heritage Garden to see if the Sullivant’s milkweed was blooming. A true prairie species, Sullivant’s milkweed is exceptionally attractive to Monarchs for use as a nursery plant. This species was discovered by William Starling Sullivant in a prairie west of Columbus, Ohio in the 1840’s and was named in his honor.

The Monarch butterfly, Danaus plexippus, is unique in the insect world for its annual migration. Monarchs that breed in eastern North America migrate up to 2,500 miles to wintering sites in Mexico. Monarchs that breed in western North America migrate to the California coast for the winter.

The Monarch’s wingspan is about 3.5 to 4 inches. The average Monarch weighs 500 mg, about the same as a paperclip. The Monarch lives for only 2-6 weeks during the breeding season. During the wintering season, Monarchs can live up to 8 months.

Adult Monarch butterflies eat nectar. They are generalists and can feed from a variety of different kinds of flowers. Monarch caterpillars are specialists and eat only milkweed.

The Ohio Department of Natural Resources Division of Wildlife’s new Publication 5474 (0115), Milkweeds & Monarchs, provides excellent information about five of the native Ohio milkweeds known to host monarchs. Remember that Monarch butterflies deposit eggs on milkweed plants, which then provide nutrition for the caterpillar phase of the butterfly’s life cycle. There are 17 native milkweed species in Ohio and Monarchs will use at least 13 of them as host plants.

The five native milkweeds discussed in the ODNR bulletin include: Butterfly-Weed (Asclepias tuberosa), Common Milkweed (Asclepias syriaca), Purple Milkweed (Asclepias Purpurascens), Sullivant’s Milkweed (Asclepius sullivantii) and Swamp Milkweed (Asclepias incarnata).

Interested in adding nectar plants for the Monarch Butterflies to your “milkweed community”? The bulletin reminds gardeners that insects, including butterflies and moths, often have specific relationships with select native plants species that is dictated by the chemical composition of the plant. Non-native plants are often chemically incompatible with native insects, and as a consequence alien plants add little if anything to the food web. Native plants suggested include: Ashy Sunflower, Black-eyed Susan, Prairie-dock, Purple coneflower, Rattlesnake-Master, Dense Blazing-Star, New England Aster, Shale-Barren Aster, Smooth Aster, Spotted Joe-Pye, Ohio Goldenrod, Ox-Eye Sunflower, Stiff Goldenrod, Tall Ironweed, and Narrow-Leaved Mountain Mint.

Are you watching for caterpillars on host plants? I have a large patch of Bronze Fennel that hopefully will be home to several Black Swallowtail caterpillars in the coming days. As for the Milkweed plants at my house, the plants in the front yard are always munched on first, and then the Common Milkweed down by the vegetable garden becomes a haven for a host of insects! I have never found a Monarch caterpillar in the lower garden. Not sure why!

Don’t forget to email your gardening questions to OSUE Brown County Master Gardener Volunteer, Mike Hannah, at mhannah1951@gmail.com.

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