I’m thinking of selling, but I have just discovered that I have Japanese Knotweed in the garden. How big a problem is this?

ASK THE EXPERT

A. That rather depends on how quickly you want to move. Introduced into the UK in the early part of the 19th century, Japanese Knotweed is today the most invasive plant species in the country, capable of doing all sorts of serious damage to buildings, lifting concrete and undermining walls and foundations.

Plant-wise, in other words, we’re talking about Britain’s public enemy number one – so much so that it is actually an offence to plant it, or cause it to grow, in the wild.

That is not the case with private property. You are perfectly entitled to grow Japanese Knotweed in your garden if you wish – and there’s no denying that it is attractive, in moderation. Nevertheless, I would strongly advise you to take the necessary steps to eradicate the stuff before you put your home on the market. Any surveyor who spots it will almost certainly mention the fact in his report, and some lenders are understandably wary of it – so you could even end up losing your buyer as a result.

The good news is that Japanese Knotweed is not a completely unsolvable problem. Specialist eradication firms can certainly get rid of the stuff, using powerful chemicals. Or you can have a go yourself – by cutting the hollow stems down to about 6 inches (the best time to do this is late summer), and filling them with a suitable glyphosate-based weedkiller. You may have to do this two or three times, but it should work in the end.

Finally, a word of warning. Beware the cowboy who promises to dig the stuff up and cart it away for cash. Since Japanese Knotweed is perfectly capable of regenerating itself from a tiny sliver of root, it is virtually impossible to get rid of in this way – so it will almost certainly reappear. But in any case, all parts of this plant, and any soil contaminated with it, are officially classed as controlled waste. This means that it must be properly disposed of according to the appropriate Environment Agency regulations, preferably by a specialist waste carrier.