At the last HCERA committee meeting, we were discussing the pest plant Japanese knotweed growing near St George’s School, when someone said, “I think I have some in my garden.” Hence the reason for this article.

It is a perennial with large oval green leaves and a hollow, red-brown zigzag stem. It can reach a height of 1.5m by May and 3m by June. The plant dies back between September and November. It was introduced as an ornamental plant in the 1800s. Fortunately all the plants in Europe are female, so the flowers produce no seeds.

Because of its rampant spread and ability to shade-out native plants, it is an offence under the Wildlife and Countryside Act 1981,’to plant or otherwise cause to grow in the wild’ Japanese knotweed.

If you have some in your garden, how can you get rid of it? Digging it out will only spread the problem as new plants will grow from even tiny pieces of root and so it must not be put in the green garden-waste bags. Spray the foliage with glyphosate when about 3ft high, usually in May, and any regrowth in the summer. Continue until it is eliminated, which will take several seasons.

For more information see
Japanese Knotweed Alliance
Royal Horticultural Advice on Japanese Knotweed

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