Eradication and Control of Perennial Weeds

Weeds are plants that spread rapidly and invasively without deliberate planting, growing amongst crops and competing for light, water and soil nutrients. Crop yields will be reduced. Furthermore, the roots of couch grass have pointy ends capable of spearing root crops and allowing entry to plant pathogens. Effective elimination of perennial weeds before planting crops is therefore essential.

Removal of Woody and shrubby growth

Gardeners taking over a plot left unworked for several years may be faced with the job of clearing woody growth. Species colonising unworked ground are commonly brambles, gorse, hazel, elder, alder, willow and ash. Small areas can be cut down using hand tools - loppers, shears, secateurs and slashers. Larger areas of shrubby growth may need a petrol-driven brush cutter. Large trees of 5m (15ft) or more should be cleared by felling with great care. As much of the woody roots as possible (i.e. all!) should be removed when digging the soil for the first time. Whilst clearing shrubby growth is heavy work, soil previously overgrown by shrubs has the advantage that many smaller weeds have been outcompeted and soil has been mulched by several years of leaf fall.

Control of Smaller Perennial Weeds

There are several viable control strategies for smaller perennial weeds. All begin with cutting to 25-75mm (1-3 inches) of the ground.

Chemical Control

After cutting back, a systematic herbicide should be applied. This will effectively kill the plant, including the root. 3 or more applications may be necessary. Take care not to use a chemical that persists in the soil

Light Exclusion

Light can be excluded with thick black plastic or old carpets. After 1 month, all green foliage will have died completely and roots loosened in the soil, allowing them to be easily removed be digging with a fork, not a spade. After 6 months, roots are also effectively killed. The image on the left shows an area infested with couch grass; to the left of the image ground has been left, to the right ground has been covered by carpet for two months

"Quick" Manual Control

To clear "quickly" by hand, dig the soil using a fork, pulling out roots as whole as possible. Shake off as much adhering soil as possible, then bag up for disposal in municipal green waste. Do not add to any domestic compost heap; it is unlikely to be hot enough to kill the roots and they will start growing through the compost. Roots can also be dried out and burned. A final safe disposal method is to submerge in water and exclude light. The roots will rot to produce a foul smelling but highly nutritious liquid feed.