Are All Milkweeds Good For Monarchs?
There was an interesting article in the New York Times on Monday about Monarch butterflies and milkweed. The takeaway is that planting Tropical Milkweed (Asclepias currasavica) may do more harm than good, according to several researchers.
Milkweeds, of course, are the only plants that are eaten by the caterpillars of Monarch butterflies.Changes in farming practices have led to a huge decrease in the number of native milkweeds. This in turn has been perhaps the chief cause in the decline of the Monarchs. As a result, gardeners have been encouraged to plant more Milkweed – but not all Milkweeds are created equal.
The danger from Tropical Milkweed is two fold. First, the availability of Tropical Milkweed in the fall and winter may disrupt the migration behavior of Monarchs – so that they settle down and breed instead of continuing their journey to Mexico. This is more of an issue in the Southeast than the Midwest.
Second, there is some evidence that Monarchs feeding on Tropical Milkweed are more likely to be infected by a harmful parasites.
There is not unanimous agreement that Tropical Milkweed is a serious problem. Chip Taylor of Monarch Watch believes that the plant is probably not beneficial to Monarchs but is not likely to cause “immense harm”.
I’ve grown Tropical Milkweed (which in Chicago is an annual) in containers and found it rather unsatisfactory. I much prefer perennial native Milkweeds such as Butterflyweed (Asclepias tuberosa) and Swamp Milkweed (Asclepias incarnata).
Butteflyweed prefers well-drained soil, while Swamp Milkweed (not surprisingly) likes moisture. In my opinion they are both much more attractive than Tropical Milkweed.
Even if the evidence against Tropical Milkweed is not conclusive, it just makes sense to stick with the natives.
Do you grow Milkweeds in your garden? Which species do you like best?