The email from my neighbor to the south was ominous. “There’s a plant I’ve never seen before on the north side of your property along the road. It’s already grown into a big patch and I’m afraid it might be swallowwort.” I had read that swallowwort was highly invasive, but I had never seen any around here. Still, any plant that appeared suddenly and in large quantities needed to be investigated. We’re already trying to keep wild parsnip and garlic mustard from taking over, and we’re fighting Tartarian honeysuckle as well. We sure didn’t need another invasive species in the neighborhood.
I walked over to the area my neighbor had described, and realized I had mistaken the plants he was talking about for milkweed. But now that I looked carefully, I realized this was something else. I took a few pictures and went inside to research. Between my reference books and the internet, I finally figured out it was hemp dogbane (Apocynum cannabinum).I had never heard of or seen this plant before, and yet according to the USDA, it is native to all fifty states. It’s not surprising that my neighbor mistook it for swallowwort and I mistook it for milkweed, because all three are from the same family (Apocynaceae) and have similar leaves and flowers. All three have rootstocks that creep underground, making large colonies, and have those distinctive seedpods that open up, releasing lightweight flying seeds into the air.
Are your warning bells going off yet? The Ladybird Johnson Wildflower Center warns, “This species can become a serious weed as it is aggressive and difficult to control.” Illinois Wildflowers notes “In moist open areas, clonal colonies can spread aggressively from underground rhizomes.” Penn State Extension gets more explicit: “Ten-day-old seedlings already have perennial capabilities; they can resprout if cut off at ground level. Roots grow laterally and send up new shoots, so one hemp dogbane plant can quickly turn into a large patch. In fields under cultivation, tillage chops the roots into small pieces. A root segment less than one inch long with a single bud can produce a new plant.” By now I am hyperventilating. This plant will take over the world, if you let it.
But it’s a native plant!
What good is dogbane?
Aren’t native plants good? Don’t we want them in our gardens? Not if you’re a corn farmer: “Control in corn is difficult because hemp dogbane seedlings emerge one to three weeks earlier than corn seedlings, and shoots continue to emerge throughout summer.” I noticed Nan Ondra had a picture of hemp dogbane in her recent blog post. I asked her how hemp dogbane behaved in her field. Her answer? “It’s more aggressive than goldenrod.” Uh-oh. I had to remove goldenrod from one of my garden beds; it just took over. I’d better be on the alert.But Nan also pointed me to What Good is Dogbane?, which pictured over a dozen different pollinators that feed on hemp dogbane. Yes, it’s a native plant, and there are plenty of bees, butterflies, moths, beetles, bugs, and flies that feed on it.
It’s only a matter of time before it shows up in the lawn. Will weekly mowing keep it in check? Sooner or later, it will show up in my flower beds–if it hasn’t already. Will I recognize it in time? Right now it’s on the very edge of our property, along a creek–the equivalent of a fence row. Should I try to curb its growth, without trying to eradicate it, or let it do whatever it wants? What do you think?
Posted for Wildflower Wednesday, created by Gail of Clay and Limestone, to share wildflowers/native plants no matter where you garden in the blogosphere. “It doesn’t matter if we sometimes show the same plants. How they grow and thrive in your garden is what matters most. It’s always the fourth Wednesday of the month!”