Sometimes nature comes a little too close when there is disturbed ground. One of the common invaders is Japanese knotweed. This shrubby plant in the knotweed or buckwheat family was imported in the late 1800s as an ornamental curiosity and became a rampant escapee in our area. You may have seen it lining roadsides or stream banks. It spreads by both seed and runners. Therefore, it is important to never let the plant flower. Attempting to dig it out is futile since the roots go down several feet.
At PBOG, we are controlling this plant weekly in our own nursery area in Ayer. A large stand had been allowed to grow over time unchecked at the edge of our space. We find the most effective way to weaken the plant over a period of several years is to repeatedly cut the stems once the plant reaches 6” in height. Cuttings are then dried out on a pallet and composted once they lose their biomass.
If you have knotweed stems sprouting in your garden, adopt this practice. Then plant a native tree or shrub to shade out the knotweed, since this plant prefers full sun. We like to use Aesculus parviflorus, Bottlebrush Buckeye, for this purpose. This native shrub is fast-growing, broad spreading, and has large leaves that will shade out the weakening knotweed plants.
An alternative natural control method for Japanese knotweed is to inject the stems with an undiluted solution of 30% horticultural vinegar. This is rather more time-consuming but effective.