Invasive Profile: Butterfly Bush

Don’t fall for the seductions of Buddleia davidii. The butterflies will thank you.

Gardens move us. Which perhaps explains why gardeners can get emotional while discussing their favorite dos and don’ts.

I recently had a funny exchange with a Facebook friend who’s battling an invasion of Japanese knotweed. Shooting a bit from the hip (this aggressive plant is one of the few invasives we don’t seem to have at Puddock Hill—fingers crossed!), I advocated for my preferred non-chemical method, which involves getting out the string trimmer and deploying said instrument with mortal prejudice.

Mais non! one of her other friends objected, coming close to calling me an idiot. Apparently applying a string trimmer to Japanese knotweed in some circles is the equivalent of releasing the kraken. She shared an official-looking Irish website that asserted it is literally illegal in that country to “strim” this plant because doing so spreads it further.

Gosh, this makes me want to get snarky, but I’ll refrain.

I confess to not having studied Japanese knotweed. I am well aware that it’s a noxious weed, and noxious weeds are by nature aggressive. But, c’mon, they’re not triffids. The Irish law—if it’s really a law—was probably instituted because people get lazy about cleaning their equipment, which is a bad practice indeed, and can be a great way to inadvertently spread anything if you’re walking up and down the road with it. But here we’re talking about a homeowner killing something (or at least attempting to) in her own yard.

There is little question that Japanese knotweed, like so many invasive plants, is hard to eliminate. I found a case study where some guy tried string trimming every two weeks with poor results and eventually had to bury it under fabric and two feet of wood chips. There is no insinuation, however, that his unsuccessful attempts at string trimming led to WW III.

Penn State Extension says one cannot outright kill Japanese knotweed solely with string trimming, although they do suggest reducing the plant with a string trimmer before spraying it with herbicides. (For the record, Penn State always suggests herbicides.) But, again, no mention of the equation: string trimmer + Japanese knotweed = armageddon.

Anyway, I skulked away from that Facebook discussion. But at least all parties involved knew the plant in question was bad.

What to do about those who proselytize for plants that harm nature?

A year or so ago, I spotted some European gardener advocating for butterfly bush (Buddleia davidii) to her large Twitter following. I gently informed her that butterfly bush is considered invasive in many places, including England, where it famously dominates train rights of way.

Judging from her response, I may as well have insulted her children. I unfollowed her. (And, it should be noted, I’ve mostly abandoned Twitter because I find Elon Musk even more petulant.)

Then, more recently, a gardening Substack to which I subscribe recommended butterfly bush as a great bloomer for the summer lull. I decided not to engage in discussion there, but I note here that her newsletter is not among those I recommend, precisely because it often seems tone deaf to the tenets of backyard stewardship.

To be perfectly clear, in the United States butterfly bush is considered invasive on a good portion of both coasts and well into the Midwest, in addition to British Columbia in Canada, as this USDA map shows:

How can this be? Don’t butterflies delight in its flowers this time of year? Yes, and that’s part of the problem. Like many invasive plants, butterfly bush matures quickly, crowding out natives, and produces a profusion of seeds—40,000 on a single flower spike. It attracts butterflies, of course, but no caterpillars can eat it. So if a butterfly lays eggs on this shrub, the resulting caterpillars starve to death. As the backyard steward knows, if you don’t support the full lifecycle of a species, you soon have fewer of them and you may one day have none.

As usual, if you want to see and support butterflies, the better course is to plant native pollinators, as noted in articles from Penn State Extension (whence I stole the map above), Brandywine Conservancy, and The National Wildlife Federation, among many others.

I confess to once laboring in ignorance about the harms butterfly bush can do. We had one or two of these shrubs both in Bedford and North Salem, NY, and later even at Puddock Hill. But when I saw the light, we pulled them up. Butterflies are worth fighting for.

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A native Eastern tiger swallowtail butterfly (Papilio glaucus) feeds on a native Stokes aster (Stokesia laevis) cultivar near the raised bed garden:

Speaking of raised beds, we haven’t checked in with Pam’s beds in a while. Hello, dahlia!

Native coneflower cultivar (Rudbeckia spp.) after a rain:

Native to Mexico and Guatemala, this marigold (Tagetes spp.) looks right at home at the moment:

This showy aster is undoubtedly not native:

In the shadow of a stone wall, American marshpennywort (Hydrocotyle americana) thrives among the gravel:

It’s easy to overlook its tiny flowers: