Knot what the doctor ordered

Now almost complete, the three-block development, called Brazabon Park and built for developer Terrace Hill, occupies a former British Aerospace site. Once home to the firm’s canteen, the site was dormant for 30 years. Japanese Knotweed, originally imported by wealthy Victorians to fill up their vast gardens, moved in.

Japanese Knotweed is tenacious stuff and can penetrate tarmac and unreinforced concrete. ‘It’s pretty powerful, if it sees a chink of light it will grow towards it,’ admits Patrick Leydon, managing director of ground remediation specialist Leydon Kirby Associates, which was brought in to deal with the problem.

The other problem is that it does not require pollination to procreate. Instead, a tiny part of its underground stems, known as rhizomes, is all that’s needed to produce a new plant.

There are several ways to get rid of it. If you’ve got a few years, use herbicides. If you’ve got lots of money, dig and dump, because soil containing Knotweed is treated as contaminated land and costs £30-£50 a tonne to dispose of in landfill.

At Brazabon Park, Leydon Kirby dug up the weeds and sifted through the soil to remove the rhizomes, which were then burnt. The contractor then buried the sifted soil at depth: below two metres to make sure the Knotweed didn’t rise again, and on parts of the site outside the new buildings’ footprints.

For Stradform contracts director Nigel Jones, the weed was one of several potential problems in the ground. There was also a possibility of finding Second World War structures and Roman remains. The contractor employed an archeological consultant on a watching brief. Happily, no remains were found.

Meanwhile Leydon Kirby, which set up its specialist Japanese Knotweed unit three years ago, is working on several sites around the country. You could say it’s a growing business…