Which Native Milkweeds Are Best For Monarch Butterflies?
Monarch Butterflies need Milkweeds (Asclepias sp.), right? Because Monarchs lay their eggs on Milkweeds and only Milkweeds. But when it comes to attracting and supporting Monarchs, are some Milkweeds better than others?
Scientists from several universities have recently published some research on this very question. I became aware of this study thanks to Sue Dawson, who started the Facebook group Gardening with Nature in Mind.
The researchers tested 9 species of Milkweed over three years. All were native to the Midwest. Plots of each species were established at research farms operated by Iowa State University at different locations throughout the state. They recorded the number of eggs laid and the survival rate for the resulting caterpillars (larva).
Turns out the best Milkweeds overall are Swamp Milkweed (A. incarnata – also called Rose Milkweed) and Common Milkweed (A. syriaca), which scored high for both egg-laying and caterpillar survival. Gardeners tend to avoid Common Milkweed because it is pretty aggressive, but Swamp Milkweed can be found at many garden centers.
I was disappointed that Butterflyweed (A. tuberosa) scored low for number of eggs, though it does well with caterpillar survival. Butterflyweed is my favorite Milkweed for 3 reasons: its mounded habit, its tendency to gradually grow into large clumps instead of running all over the place, and (most of all) those incredible orange flowers.
It’s a funny thing, too, because I have plenty of Swamp Milkweed but have seen Monarch Caterpillars in our garden only on Butterflyweed.
For gardeners, it makes sense to plant a variety of Milkweeds. If at all possible, that variety should include Swamp Milkweed. Though it naturally grows in moist to wet soil, Swamp Milkweed does OK for me in fertile soil that has just medium moisture. In addition to Swamp Milkweed and Butterflyweed, we currently have Prairie Milkweed (A. sullivantii) in our garden – and I’m trying to establish some Poke Milkweed (A. exaltata) as well.
And I wouldn’t plant Common Milkweed unless you have a lot of space or are ready to engage in a long-term struggle against a ruthless expansionist. Another Milkweed to avoid is Honeyvine Milkweed (Cynanchum laeve), which can be a real pest and is not ornamental at all. Plus it does poorly at Monarch caterpillar survival.
If you want to read the article yourself, here’s a link.
Have you noticed if Monarchs prefer a particular Milkweed species in your garden?