Clippings: news and views
Our roundup of e month’s latest gardening news and views
A knotty problem
Does Japanese knotweed deserve its bad reputation as an invasive weed capable of destroying buildings? In the past, the weed’s presence has affected property prices and those buying property with Japanese knotweed have struggled to get mortgages, but new research suggests that the problem is not that bad. Studies by the University of Leeds and infrastructural services firm AECOM found that there is “no evidence that Japanese knotweed causes significant structural damage.” Japanese knotweed is believed to cause problems to structures that are within seven metres of the above-ground part of the plant – which is known as the ‘7m rule’. It can regrow from very small bits of its underground roots or rhizomes, which makes it difficult to dig out. Yet the university’s research showed, in a survey of 81 excavations of the weed, that “rhizome spread was generally less than 2.5m.” Dr Mark Fennell, principal ecologist at AECOM said, “We found nothing to suggest that Japanese knotweed causes significant damage to buildings and certainly no more damage than other species that are not subject to such strict controls.” Legally, since 2013, a seller is required to state whether Japanese knotweed is present on their property. A report following a July 2018 YouGov poll on the weed said that it can cost £166 a year to treat the invasive weed. But Dr Karen Bacon, from the University of Leeds said: “Japanese knotweed is capable of damaging built structures, but where this occurs, it is usually because an existing weakness or defect has been exacerbated. The impact of Japanese knotweed on factors such as biodiversity and flooding remains a concern, but this plant poses less of a risk to buildings than many woody species, particularly trees.”
Japanese knotweed poses less of a risk to buildings than trees