Indigenous to Japan, knotweed was originally shipped westward by German botanist Philipp von Siebold who packed up a variety of plant specimens and took them to both the Utrecht plant fair in the Netherlands in the 1840s and to the Royal Botanical Gardens at Kew back in 1850. Japanese knotweed (Fallopia japonica) looks like a nice little shrub with heart-shaped leaves, bamboo like-stems and pretty, little white-flowers. Those sweet looks are deceiving, though, as the plant is absolutely relentless.
Von Siebold's sampling of knotweed took root in England and quickly spread across Europe and then to the U.S. where it now has taken root in 42 states, including many in the South. Luckily, it may be too hot in parts of Texas and Florida for the pernicious plant to survive, but it has undoubtedly tried. Japanese knotweed is what Newsweek dubbed, "a rapacious monster."
It takes over gardens, choking out other plants with its towering shoots that can grow up to six feet tall and a whopping 65 feet wide. No offense to your prize camellia, but the garden is the least of your worries with Japanese knotweed. The roots and shoots of this fast-growing plant spread underground, unseen, until it pops up in your patio, your concrete walkway, the path to your pergola, even the floor of your basement. It can ruin your home's foundation and even make your home unsellable.
You can't just pull Japanese knotweed out of the ground, either. The plant is nearly unstoppable 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. Japanese knotweed is so hard to remove that, according to Groundworks Companies, "some states' mortgage lenders require homeowners to declare its presence on a property when selling the home." 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."
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 Companies, 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.