As somebody who likes insects, I’ve been monitoring my perennial pollinator plants to make sure they made it through winter and will provide food for pollinator insects this year. I’ve been pleased to see that my bee balm, cardinal flowers and asters are thriving. I’ve also found many small, new common milkweed (Asclepias syriaca) plants in my yard and garden.
Common milkweed reproduces vigorously; while gardening and attempting some transplants, I found one tuberous rhizome (root) with eight milkweed plants coming up off of it. I knew that milkweed was prolific, but seeing so many plants off of one tuber was fascinating. Those things can really reproduce!
Actually, milkweed’s ability to spread so speedily is one reason it’s often considered a weed. But, I find it easier to tolerate their abundance knowing that some so-called weeds, like milkweed, are the main food source for some beneficial insects. This means that it is ultimately to our benefit to tolerate some of these aggressively reproductive plants.
Monarch butterflies (Danaus plexippus) will only lay their eggs on milkweed, and one other plant closely related to milkweed called smooth swallow-wort. Monarch caterpillars can only eat milkweed and this one close relative. Milkweed is important to monarchs because monarch butterflies become toxic to predators by storing toxins from the milkweed plants that they ate during their caterpillar stage. These toxins can be distasteful and harmful to predators, meaning that eating milkweed has become an important defense mechanism for monarchs.
Adult monarchs, the butterflies, consume nectar from a diversity of flowers, but again, the caterpillars can only eat milkweed. But monarchs aren’t the only insects for which milkweed is a useful food source. Many insect species consume nectar from milkweed’s flowers and some insects will eat other parts of the plant, too.
Although some milkweed species can inhabit disturbed areas and spread quickly, which are common characteristics in many plants we consider weeds, milkweeds are not listed as noxious weeds in any state or at the federal level. In fact, there are over 100 species of milkweed which are native to the United States. Legally, it’s okay to tolerate them on your property.
I do have some tips for slowing or mitigating their spread, should you wish to do so. You can pull off the seed pods before they turn brown, or mow unwanted plants. These methods will limit their spread via seed. You can sever a rhizome so that you have fewer plants coming off it, but you will continue to get new plants from that root in the future. Another option is to try to transplant the milk weed rhizomes to a place on your property where you wouldn’t mind them spreading.
Overall, if you can tolerate some milkweed in your yard, field, or garden, just know that you are helping feed our monarch caterpillars and some other insect species as well.