ICAUGHT up with Alan Titchmarsh at the recent BBC Gardeners’ World Live show when he was giving advice on how to combat Japanese knotweed, the peril of many gardeners, a weed which is right up there on the list of seemingly indestructible thugs.

“It was brought into this country as an ornamental plant by the Victorians, who thought it was beautiful,” he said.

It has an underground network of tough, fast-growing rhizomes which makes it really difficult to control and, in the summer, the bamboo-like stems grow to more than 2.1m (7ft), suppressing all other growth.

The RHS advises that if you’re going to try digging it out, remove as much root as possible, then repeatedly destroy regrowth.

In this way the energy reserves in the remaining underground parts will be gradually exhausted but this process could take a very long time. Another option is to place a layer of carpet over it but you will have to leave it a long time before it dies and you can dig it up. When you dispose of the plant, do so carefully, allowing it to dry out before burning.

Whatever you do, don’t put it on your compost heap or into your normal household waste because it colonises without seeding.

Alan, whose second ITV1 sixpart series of Love Your Garden is currently being shown on Tuesday nights, says the best time to tackle this incessant weed is when it’s in flower.

“Chop it down to ground level and when it starts to regenerate and particularly when it’s flowering, that’s the best time to spray Japanese knotweed,” he said.

He says it’s more susceptible to systemic weedkillers such as Roundup later in the season.

“Give it one big blast in autumn or late summer when it starts to flower,” he advises.

If it’s coming through from a neighbour’s garden, you will need to put a physical vertical barrier in the soil, digging a trench not less than 2m deep and inserting a tough, impenetrable membrane into it.