Stemming the Japanese knotweed invasion
JAPANESE knotweed. If you have it on your property and want to sell or remortgage you are likely to know how this tall, verdant shrub, with white flowers in late summer, can all too easily alter your plans, and even wipe value from your property.
Japanese knotweed was brought to Europe in the 1840s by a Dutch horticulturist who, in turn, sent plants to the Royal Botanic Gardens in Kew in 1850. This previously unseen plant suited the new Victorian style of wilder, softer gardening and it became a popular, and prized, specimen plant. Sharing cuttings, and the plants travel through water courses and contaminated soil being moved for construction and road building meant that by the late 1800s Japanese knotweed had begun its invasive path. In 1981, it was one of only two plants, the other being Giant Hogweed, that was proscribed in the Wildlife and Countryside Act, making it an offence to “plant, or otherwise let grow, in the wild”.
All Japanese knotweed plants in this country are female, so is it unable to reproduce via seed. Its relentless march across riverbanks, railway lines, waste land and into our back gardens has been caused by humans. In 2017, research from the Crop Protection Association revealed that it is costing property owners thousands of pounds each yea – 20% of those surveyed said it had lowered the value of their home, and 60% reported that the weed had damaged their garden or destroyed something on their property.
Many myths abound about this pernicious weed. It cannot grow through concrete but it can grow through voids within concrete, or cracks in foundations or tarmac, through drains and garden walls. It is not illegal to have Japanese knotweed on your property but it is illegal to allow it to spread. If you do you could end up in a costly legal dispute with your neighbours. It is true that mortgage companies are loathe to lend on a property if Japanese knotweed is present. To do so, they will require a Japanese Knotweed Management Plan alongside an A* rated Insurance Backed Guarantee (IBG), both of which will be available from a reputable Japanese knotweed eradication company.
If you do have it on your land, don’t wait until your prospective buyer’s surveyor spots it and the whole house move splutters to a halt. Get organised quickly – now is the perfect time of year as the plant will begin to push through the earth in March and April. New shoots, which often look rather like asparagus, have a red or purple tone. They sprout up
‘In 1981, it was one of only two plants, the other being Giant Hogweed, that was proscribed in the Wildlife and Countryside Act, making it an offence to “plant or otherwise let grown, in the wild”’
from the rhizome which can be up to three meters deep and lie dormant for many years. As spring progresses the plant grows rapidly. The bamboo-like stems are hollow, and often speckled red, or with red joints and knots. By summer the plant can reach over three metres high and will be covered in lush, green, shield or heart-shaped leaves up to 22cm long. In late summer it develops clusters of spiky stems covered in tiny white flowers. In late autumn, the leaves fall and the canes go brown. But be aware, it is not dead, it is storing energy deep in the rhizome ready to repeat the process the following year.
Treatment options – herbicidal and, as an organic alternative, but not appropriate for all sites, digging it out. The chemical route takes a number of seasons to completely eradicate all parts of the plant. It is possible to sell your home while this is going on, with the caveats relating to Management Plans and IBGs. For an average residential infestation eradication should cost in the region of £2,000 - £4,000.
With the right equipment, the plant and the rhizome can be dug out. The rhizome is brittle and a piece left behind, just the size of a fingernail, will regenerate. It is an expensive method and may not be suitable where access to the site is difficult. The soil, rhizome and canes can only be disposed of in a licensed landfill, as it is classified as controlled waste, just as any canes you cut down in your garden cannot go into the council recycling bins.
Don’t be fooled into thinking it’s dead in winter - it’s simply getting ready to return
By summer Japanese knotweed will produce spikes of small white flowers
Look for reddish brown asparagus-like shoots in spring