Japanese Knotweed is one of Britain’s most invasive non-native plants. First introduced to Britain in the mid-19th century as an ornamental plant, it’s annual rapid growth allowed it to easily overrun land and gardens.
Japanese Knotweed is well known for its vigorous creeping root system (fibrous rhizome) and can cause horrendous damage to building foundations, drain systems, underground utility services, walls and much more.
If that isn’t bad enough, Japanese Knotweed can also contaminate the soil with reproductive knotweed material covering areas of up to 3 meters in depth and 7 meters in radius. In these extreme circumstances, the Environment Agency recommends the removal and treatment of affected soil.
How to identify Japanese Knotweed?
As the name suggests, Japanese Knotweed is a weed, however unlike most weeds, it is very decorative and most people don’t even realise the potential problems it can cause.
With a similar appearance to Bamboo, Japanese Knotweed is a perennial weed that produces tall canes that can reach up to 7ft during the summers months. The speckled red canes produce a network of red zig zag leave stems with bright green ‘shield’ shaped leaves.
In the Spring and Summer, Japanese Knotweed stems grow tall and produces leaves that are up to 14cm in length. In late summer the plant produces white tassel like flowers. In Winter, the stems die back to ground level.
How to Control Japanese Knotweed?
If you have Japanese Knotweed on your land it is vital that you prevent it spreading or you could be liable for prosecution. As one of the biggest spreaders, only a small amount (less than a centimetre) of knotweed root (rhizome), can form into a new plant.
Non Chemical Control:
Digging out the weed id possible, however due to the depths the rhizomes can reach, regrowth is almost guaranteed. By digging the root out, you also have a problem with disposal. Japanese Knotweed is classed as ‘controlled waste’ under the Environmental Protection Act 1990 and requires disposal at a licensed landfill site. Alternatively, it can be destroyed on site by allowing it to dry out before burning. On no account should Japanese knotweed be included with normal household waste or put out in green waste collection schemes.
A glyphosate based weedkiller is probably one of the most effective and simplest method for the home gardener to tackle Japanese Knotweed. Always follow directions from the manufacturer to ensure proper eradication of the plant and protection of you and your environment. It usually takes at least three to four seasons to totally eradicate Japanese knotweed using glyphosate.
Get help from a professional:
Professional contractors, however, will have access to more powerful weedkillers that may eradicate the species in 1 – 2 seasons, depending on the maturity of the plant. Specialist Japanese knotweed contractors are usually licensed to safely remove the weed from site but check first before employing their services.
Future control of Japanese Knotweed:
Biologists are currently testing a plant sucker in the UK for the biological control of Japanese Knotweed. This is currently being tested at only a handful of trail sites, but if successful will be released more widely across Britain over the next 5 to 10 years.
For more information on what to do if you think you have Japanese Knotweed in your garden, visit the Royal Horticulture Society
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