2 Words to Instill Terror in the Heart of Any Gardener: Japanese Knotweed

Melissa Locker
·2 min read

This species of knotweed originating in Japan was originally shipped westward by German botanist Philipp Franz von Siebold, who, after spending time in Japan, brought them to the Netherlands in the 1840s. Japanese knotweed (Fallopia japonica) looks like a nice little shrub with heart-shaped leaves, bamboo like-stems, and pretty, little white flowers. Its sweet looks are deceiving, though, as the plant is absolutely relentless.

Von Siebold's sampling of knotweed took root in England, quickly spread across Europe, and then to the United States, where it has now taken hold in as many as 42 states, including many in the South. Luckily, it has not seemed to establish itself in some states in the south. Japanese knotweed is what Newsweek dubbed, "a rapacious monster."

Japanese Knotweed
Japanese Knotweed

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Japanese Knotweed Spreads Far and Wide, Above and Below Ground

It takes over gardens, choking out other plants with its towering shoots that can grow to be 10 feet tall. No offense to your prize camellia, but the garden is the least of your worries with Japanese knotweed. The persistent taproots of this plant spread underground, unseen, until it pops up through your patio, your concrete walkway, the path to your pergola, even the floor of your basement. It can even damage your home's foundation, and is a growing concern for homebuyers and sellers alike.

Just When You Think It's Gone

You can't just pull Japanese knotweed out of the ground, either. The invasive plant is extremely difficult to contend with and, according to Newsweek, "can take up to five years of regular chemical blitzing before the knotweed all-clear can be sounded." That's because even a small amount of root left growing under the soil can regrow and turn into another plant, starting the whole process over again. It's such a destructive plant that, according to Slate, "in the United Kingdom, it has been a crime to plant or transport unsealed knotweed since 1990."

Eradicating Japanese Knotweed

So what's a homeowner to do? If there is Japanese knotweed on your property, there's most likely a long and difficult weed-killing road ahead. Groundworks, which works in the home services industry and specializes in foundations, has a season-by-season guide that mostly entails digging that sucker out by the roots, being sure to get every last bit of the plant out of the dirt, bagging it up (do not compost!), and shipping it out. In fall, weed killer will be your friend to ensure that Japanese knotweed is truly eradicated. If you do spot the little monster, Groundworks also suggests calling in a professional to inspect your home's foundation, lower-level crawl spaces, and basement to make sure there's no damage.