The unstoppable Japanese knotweed

Beautiful but beastly Japanese knotweed isn’t all that horrible to look at really, particularly in the summer when its lush green leaves and small white flowers give it a pleasant appearance. Heck, you can even eat the stuff (it tastes like rhubarb). But despite this, Japanese knotweed is a problem for a variety of reasons. Japanese knotweed growth Japanese knotweed can grow at an exponential rate, up to 10 cm in a day, so it can quickly envelope any biosphere it gets its roots into. It is also an incredibly adaptable plant, strong enough to break through timber and even cracks in concrete, to reach areas with more sunlight. Left alone, Japanese knotweed can grow up to 4m metres high. So, you cut it down and dig it up, right? Wrong!

Cutting back Japanese knotweed will simply cause its roots to grow in search of nutrition from soil. If the knot weeds root system reaches through an entire garden then it is not uncommon for knotweed to damage garden sheds, furniture and even the exterior of homes. Knotweed can be dug up but it is a very labour intensive process. The soil must be sifted through to make sure no remnants of the Japanese knotweed remain. Even a small Japanese knotweed rhizome of only a few centimetres can trigger a whole re-growth.

So, If you have Japanese knotweed, are you stuck with it? Not really; Japanese knotweed can be chemically treated with herbicides. However, these are not at all kind to the environment and the chemicals must be injected into the stem of the knotweed and also applied to the leaves. This treatment is the most effective way to destroy knotweed but it can take ten applications of herbicide over five years to completely eradicate the weed.

How to identify Japanese knotweed

If you suspect you have Japanese knotweed in your garden or that it is growing in a neighbouring property you can identify it by recognising its different appearances throughout the seasons.

Spring: Knotweed will begin its growth in the spring. It will initially look like small shoots of asparagus before sprouting green spade shaped leaves.

Summer: The knotweed will now begin to grow at an exponential rate and begin to sprout small white flowers.

Fall/Autumn: The knotweed leaves will begin to turn yellow and the stems will turn from maroon to dark brown. There will also be a distinctive zig-zag effect on the stems at this time of year.

Winter: during the winter months the knotweed stems die off and whatever is left of them resemble hollow, brittle twigs. That said, the knotweed remains dormant underground to continue its life-cycle again in the spring.

Japanese knotweed – bad but beatable Japanese knotweed may be gardening’s most unwelcome guest but it can be eradicated with the right treatment, time and effort. Early identification and knowledge of the plant will prevent a minor outbreak becoming a full-scale knotweed invasion.