Japanese Knotweed was considered ‘a capital plant for the small town garden’ back in the 19th Century. Today you can be fined up to £2,500 for not preventing the spread of this invasive plant.
RDEFA have ‘no plans’ to eradicate the plant due to the ‘prohibitively expensive’ $1.5 billion cost that is attached, so why do we want to get rid of it so much?
It’s the plants wide ranging and fast growing root system or rhizomes that cause the problem. They explore areas for cracks and openings into which to grow at the rate of more than a yard per week. Once in a crack, the expanding growth can exert considerable sideways pressure that can, over time, cause significant damage to built structures, tarmac and hard-standing. This damage can reduce property values by as much as 20%.
Digging only makes matters worse as rhizome fragments are also easily excavated and spread when soil is disturbed so what can be done to prevent the plants growth? It can be sprayed, or injected with herbicides directly into its stem but these can take 6 months to take effect and are expensive
Identification can be tricky at this time of year as the rhizomes are dormant and any previous year’s growth could have been cut back although dead canes can be a clue. During the spring/summer the plant can be identified by;
- dense thickets of green, purple-speckled, bamboo-like stems around three meters tall
- heart-to-shield-shaped leaves
- alternate leafing pattern along stems
- completely hollow stems that can be snapped easily
From a building survey perspective, we always ensure as much evidence is collected as possible, such as photographs and suggest a specialist knotweed survey if there is any doubt or if the property is in a high risk area e.g.
- local water sources, such as culverts, ponds, canals and lakes
- public and private paths, cycle-paths, roads,
- railway or underground railway embankments,
- dual carriageways and motorways
- large open spaces, car parks and cleared sites, and
- commercial and industrial buildings, workshops, storage depots and similar
We also keep up-to-date with the latest RICS guidance (detailed in this post) and use online tools such as Plant Tracker
If you think your next property may have a Japanese Knotweed problem please as one of our surveying team for advice.