These weeds, they’re a killer

Hogweed in a cage.
Hogweed in a cage.

One certainty when visiting allotments is that among all the tidy plots you are going to find at least one gardener who has taken over a weed-infested area and is anxious to explain how it has been transformed.

Troublesome though they are, we can all live with annual weeds. Run through them with the hoe at the beginning of a dry, sunny day and by nightfall they are lifeless. It’s the pernicious perennial types that were sent to try us. Ground elder, couch grass and horsetails brush aside herbicides as their rhizomatous roots seem to march endlessly underground. The only sure control is achieved by mechanical means – constantly digging up and removing by hand.

But there are three further weeds that are even more menacing and so difficult to control. They should not be propagated from or disposed of without due care. One was present at the allotments in seedling form. The Himalayan balsam, a giant impatiens (busy Lizzie) whose seed pods explode when ripe. It favours damp soil conditions and is found along our rivers and streams.

Second in this terrible trio is the giant hogweed (heracleum mantagazzianum), which can be found growing inside an iron cage at the Alnwick Poison Garden.This caution is necessary because the sap can cause painful blistering of the skin on contact, in the presence of daylight, also permanent scarring. This is a giant perennial plant that has invaded our river systems, whose control costs tens of thousands per annum.

Then there is fallopia, the dreaded Japanese knotweed. It was introduced to these shores, along with giant hogweed, by the Victorians, who saw them as potential status plants in herbaceous borders. Then they escaped to the wild and have never looked back.

Fallopia is the real villain. When it is found growing near private dwellings, first confirm the identity, then prepare to take action on an industrial scale – this plant has the ability to push up through solid, seemingly permanent surfaces.

One application of herbicidal spray will not solve the problem. For this reason alone, it is best to seek the advice of a specialist in the field. This is our closest plant match to the fictional Day of the Triffids specimen – but it can be controlled.

The leaves are heart-shaped and hand-sized. Autumn brings clusters of tiny white flowers. I am occasionally asked to confirm the presence of these monsters on someone’s property and it’s a case of once seen, never forgotten!