By Terry Twigg
(October 1, 2024) — Most people with even a casual interest in gardening can name the best-known villains in our niche of the ecosystem: bittersweet, barberry, and multiflora rose. Then there’s the one that more recently muscled its way into our awareness: the dreaded, almost-impossible-to-eradicate Japanese knotweed. Right now it’s in bloom, so its frothy white flowers are identifiable in alarming amounts along our roadsides. But there are a number of invasives, each capable of crowding out natives, which are so common they often escape our notice. Worse, they’re still sold in garden centers, offered at bargain prices in community plant sales, or generously shared by well-meaning friends.
Two common, troublesome trees/shrubs are butterfly bush (buddleia davidii) and rose of Sharon (hibiscus syriacus). It’s easy to see why their popularity persists, as both have very attractive flowers. Butterfly bush’s lacy panicles set off more substantial blooms in a bouquet. Rose of Sharon doesn’t last well as a cut flower, but the showy blooms, part of the hibiscus family, are eye-catching in the garden. I inherited a few when I moved here. I chopped down two out of three, and after repeated chopping over time, they’ve finally given up. I left the third, which has the prettiest flowers, but pay a heavy price yanking hundreds of self-seeded offspring every summer. It has to go.
Removing these plants doesn’t have to leave a gap in your yard, because native alternatives offer similar flowers and bloom times. Instead of butterfly bush, plant clethra, bottlebrush, or elderberry (and get a bonus of berries, if you can beat the birds to them). Instead of rose of Sharon, try native members of the same family, including rose mallow (hibiscus moscheutos) and hibiscus laevis (halberd-leaved rose mallow.
Probably the most widely cultivated invasives are ground covers: Vinca, Japanese pachysandra, and English ivy. Pretty much by definition, the purpose of a ground cover is to spread quickly, colonizing large patches, and all three are all too successful at this job. Many older houses are handsomely landscaped with one or more of these, making for a lush, relatively low-maintenance garden, especially under mature trees where grass won’t grow.
Ivy is so appealing it got a bunch of colleges named after it, but the patch on the north side of my house is simultaneously trying to smother the lilacs and pull apart the siding. If sunshine can’t reach a tree because it’s covered with ivy, the tree dies. Ivy excels at killing trees (and houses).
I’ve never liked pachysandra, associating it with cookie-cutter landscaping of ‘sixties tract houses, but I’ve inherited that, too. Someone planted it along the top of the retaining wall, and from that base it has invaded the wooded hillside. When I took out the forsythia from an adjoining area, I put down thick layers of cardboard and mulch, but to no avail. The pachysandra simply bided its time, until a few months’ rain softened up the cardboard, and then renewed its assault. It creates a thick, tough mat, very challenging to remove. Another heavy project for next spring.
After my recent health issues, I’m planning to rework my courtyard to an easier-to-maintain planting scheme. I’d love to carpet the whole thing with the glossy dark leaves of vinca, especially as friends have offered to supply as much as I care to dig (“Look, I have lots.”). But while it looks good surrounding stately homes and humble homesteads alike, it’s less appealing where it has spread into neighboring woodlands, choking out native underbrush and all the wildlife that used to be there.
Some people argue that vinca can be contained with vigilance, since it mostly spreads by underground runners and not by seeds. My courtyard might even be a candidate for that, since it’s bordered on three sides and would have to cross a hundred feet of lawn on the fourth. But having to monitor it defeats the ‘low maintenance’ aspect, and even the hardest-working gardener—which I am not—will eventually be outwitted by relentless nature. My inconvenient conscience simply won’t allow that route.
Again, there are attractive native alternatives to these traditional groundcovers. Wintergreen offers slim oval leaves throughout the year, and bright red berries from late summer. Canadian wild ginger’s broad rounded leaves are another good choice for shadier areas; both the ginger and the wintergreen occur naturally in the dappled light of forest understories. In the sunnier parts I can grow moss phlox, low-growing juniper, and bearberry.
It’s hard to renounce traditional favorites, and so easy to rationalize that ‘just this once’ won’t make a difference. But it does. There are approximately 20,000 native plant species in this part of the world, and it’s estimated that a quarter of them are threatened with extinction. Time to bite the bullet.
