Okay, we all know that Japanese knotweed is an invasive species, prone to tearing up your driveway, cracking your foundation, and choking rivers and streams. But what’s the best thing about knotweed? That’s easy: it’s in bloom. Right now. Right at this very moment when no other plant is even thinking about it.
Japanese knotweed, Fallopia japonica (formerly Polygonum cuspidatum), is an herbaceous perennial in the buckwheat family, Polygonaceae. Many people think it is some kind of bamboo because of its hollow stems and raised stem nodes, but it has no relation to true bamboo, which is actually a grass.
The World Conservation Union lists Japanese knotweed among the top 100 worst invasive plants. But if you can look past that detail, it is actually a pretty plant with large spade-shaped leaves and showy cream-colored flowers. The plants may grow 5-8 feet tall in a dense, bush-like display.
At this time of year in western Washington, you can hear these bushes before you see them. They are alive with pollinators and are particularly attractive to honey bees. Many beekeepers manage to harvest a monofloral honey from the vast stands found locally. And if you don’t harvest, it makes a great late-summer boost to a colony’s winter pantry.
The honey is dark and flavorful, and many people compare it to a mild form of buckwheat honey. I’ve tried it and, personally, I don’t taste a resemblance. Still, it is good and definitely worth a try—you can often find it sold as “bamboo honey,” especially on the east coast. The sample I had crystallized quickly at a rate similar to buckwheat honey.
Bee lovers have found another use for Japanese knotweed. The hollow stems are often cut into lengths and bundled for use as native bee habitat. The stem diameters vary just enough to provide suitable housing for a wide range of tunnel-nesting bees, including mason bees and leafcutters.
The pictures below were taken in Kirkland, Washington yesterday afternoon. The owner of this invasive marvel says, “Standing next to the knotweed almost sounded like you were standing next to a hive.” She also said, “I hear knotweed is invasive and hard to get rid of. My side yard looks like I’m growing knotweed as a crop. Neighbors have the same.”
Yup, sounds like knotweed. After it conquers the yard it will conquer the house. Once the flowers die back, she should cut up the stems for native bees and get rid of the rest.