As a gardener I tend to be the gentle type. I hate to thin weaker seedlings or pull an innocent weed that had the rotten luck to grow in the wrong place. But when facing my nemesis — the Japanese knotweed that came with our property — I have a cruel streak.
Originally sold in the 1800s as an “ornamental” (garden center-speak for “kiss your native plants goodbye”), knotweed features broad green leaves on tall mottled maroon-and-green stalks. Sometimes referred to as bamboo because of its segmented hollow stems, it grows while you watch, like stop-motion photography, only in real time.
An invasive species that makes zebra mussels seem kind of charming, it spreads primarily through large networks of underground rhizomes as well as teleportation. It embodies evil. (According to UVM Extension, it’s the only North American plant that doesn’t cast a shadow or have a reflection.)
To manage knotweed by hand, you can pull it up or cut it down. Advocates of cutting warn that pulling it stimulates its roots, encouraging it to send out new rhizomes. But pullers say cutting it leaves the roots intact, allowing it to send up new shoots. Either way, any stalks you remove will re-root immediately wherever they land, so some people suggest a third approach: forlorn resignation. At least by doing nothing, you’re not encouraging it.
Still, I try. Every few days I take my hoe out to the front garden and, shouting, “How do you like me now?” I hack down the forest of four-foot-high stalks towering over my perennials and shrubbery.
But nothing ever works for long.
I have done my research, read studies, talked to landscapers. The only proven effective method of getting rid of knotweed for good is to move and hope it doesn’t track down your new address.
Some people suggest commercial weed killers. I don’t use them, for ideological reasons — and as a handy though made-up excuse for why my yard looks so unkempt — but it turns out the stuff wouldn’t be much help anyway. Though it is the generally recommended treatment for knotweed, this is in theory only; even with repeated doses of Roundup it can take years of manual control for full eradication. Maybe. At best, Roundup has been demonstrated only to put Japanese knotweed in a bad mood.
Even covering it with black plastic is pointless, as this only makes the knotweed try harder. One woman I know peeled back a thick layer of plastic after several years to discover vibrant green knotweed shoots lying in wait. Shouting “Ta-da!” they sprang up to full height within 15 minutes.
Last week, however, I read about a guy online who conducted an informal experiment on killing knotweed. He tried repeated applications of everything from boiling water to radioactive sludge. The knotweed samples guzzled most of the substances he poured on them, then belched and grew six inches.
One shoot did exhibit some token foliage discoloration under the influence of Roundup. But the two liquids that really made the knotweed curl up and beg for mercy were full-strength vinegar and, of all things, coffee. Industrial-strength vinegar can eat through bare skin, so I went with coffee. I liked the imagery: using the very substance that brings me back to life each morning to destroy that which I despise.
Two days in a row I emptied the coffeepot on a knotweed stalk near our porch, and by sunset on the second day the shoot had withered to the ground. I’d be lying if I said I felt remorse.
Of course, it’s possible the damage is only on the surface; underground, the roots may be regrouping, soon to come back with a caffeinated vengeance. And even if the coffee really works, it isn’t enough. Hundreds of knotweed stalks in my garden need poisoning, but I only have a cup or so of coffee left over each day.
Still, the grisly death of one knotweed shoot at a time is enough to give me a perverse thrill. And if the knotweed doesn’t actually die from the coffee, that’s OK, too. I’m happy just knowing it’s having a terrible time falling asleep at night.