Japanese knotweed has long been thought to be one of the most damaging plants around buildings. Stories abound of it knocking down walls and bursting up through concrete floor slabs. Eradicating it has been costing the UK economy some £165 million a year, and surveyors and insurance companies have been terrified of it.
As some of us have suspected all along, however, the dangers posed to buildings by Japanese knotweed have been somewhat overstated, and now the RICS (Royal Institution of Chartered Surveyors) has downgraded its risk assessment of the plant.
If knotweed really has caused damage, the RICS says, then it needs to be tackled. But a few clumps of knotweed in a back garden should really be no cause for concern.
This a relief, because previously, if knotweed was found within seven metres of a house, the whole garden would need to be excavated to a depth of three metres and carted away to landfill, before extensive chemical treatment and the importation of fresh sterilised topsoil.
But before we all breathe a sigh of relief, wait – there’s another vegetable enemy that we need to watch out for – Bamboo!
Yes, this feathery-topped decorative plant, also used to provide runner bean sticks (as well as being a popular vegetable in Chinese cooking) can spread for over 10 metres underground and spring up in neighbouring properties.
One unfortunate homeowner in Hampshire recently found that their neighbour’s bamboo had spread under their house and grown up inside their cavity walls, bursting out through the plaster and wallpaper in their living room, hall and kitchen. The repair bills came to £100,000.
As with most plants, there are many different varieties of bamboo, and some are more dangerous than others. It’s the “running” varieties that can send out long sideways shoots that get under walls and floor slabs and invade neighbouring buildings.
However, professional builders know that ALL plants can be damaging if they are planted too close to buildings, and not properly maintained. How often have you seen a small weed elder or buddleia sprouting out of the brickwork in a neglected building? In a few years those “weeds” can grow into trees and force the brickwork apart.
And don’t get me started on ivy. Some homeowners actually deliberately train this stuff up their walls, where it roots in the mortar joints and expands. Not to mention the build-up of dead ivy leaves that compost themselves next to the wall and allow penetrating dampness.
Still, for now we can be happy that the unjust prejudice against Japanese knotweed has been exposed and rectified. Not that I will be rushing out to plant any in my garden, you understand!
