Monarch-unfriendly invasive plants

Here are some invasive plants I make sure I don't grow in my yard.

Black swallowwort

Black swallowwort  ©Janet AllenBlack swallowwort

No one intentionally plants black swallowwort, but it may arrive anyway.

When I first saw it growing in my yard, I didn't know what it was. When I found out, I pulled it out immediately.

I've found two plants in my yard over the past few years. I suppose it might have hitchhiked on plants I bought. I'm always on the lookout for it now.

The non-native black swallowwort not only is invasive in general, but it's particularly bad for monarchs.

Unfortunately, it's a relative of milkweed, so the female monarch—checking the chemical composition of the plant with her feet—judges it to be a milkweed and lays her eggs on the leaves. The problem is that monarch caterpillars cannot eat the leaves of this non-native plant and they die.

Another serious problem is that black swallowwort takes over so much land and in such dense stands that it crowds out native milkweed, leaving even less milkweed available for monarchs.

Black swallowwort seed pods ©Janet AllenBlack swallowwort seed pods

It's easy to see black swallowwort's resemblance to milkweed. The pods are very similar, though more slender than most of the milkweeds I grow.

I took this photo at a local state park. I pointed this out to my walking companion and noted that it was a shame it was out here along the edge of our beautiful lake.

She reassured me, noting that it wasn't a problem as long as it was out here. It took me a minute to realize what she meant: As long as it wasn't messing up people's home landscapes, it wasn't a real problem!

It's pretty discouraging to learn that otherwise well-meaning, well-educated people have so little understanding of ecology and of our total dependence on healthy ecosystems.

Buddleia aka butterfly bush

Buddleia aka butterfly bush ©Janet AllenBuddleia

Long ago—before I even was able to identify monarchs in particular—I had planted quite a few buddleia. I was thrilled they did so well. They were even easy to start from seed. (Now I know why that shouldn't have been surprising.)

I discovered that these weren't a real benefit to butterflies, only to people, who want to attract lot of butterflies in close viewing range. I got rid of all of them.

There are three reasons why we don't want buddleia.

  • They've become invasive in many states, spreading into natural areas. In fact, even after not having buddleias for seven or eight years, I found one growing in my yard, right up to the blooming stage. The seeds must last a long time in the soil. I know that some people say that it's okay to have them if you remember to cut off the seed heads, but first, who really remembers to do all those things in a timely fashion and why would anyone want to add one more chore anyway? But even if this worked, this approach doesn't address the next two issues.

  • Tallamy in Bringing Nature Home notes that substituting a native plant for the non-native buddleia provides many habitat benefits, not just nectar.

  • Summers in her book Designing Gardens with Flora of the American East notes that butterflies live very short lives. If they spend their time hanging around this unnaturally attractive nectar source, they aren't looking for their increasingly difficult to find larval host plants for laying their eggs. With such a short life span, these missed opportunities can make a difference in the total population. To me, this is a compelling argument.

See the Resources sidebar on the Butterfly Food page for some alternatives to buddleia.