Mechanical control of weeds methods

Many methods of controlling herbs and weeds. About 420 of them are good but we will cover only the mechanical ones. Mechanical methods include digging, hoeing, rotovating, cutting and pulling the weeds. In digging the soil is turned over and the weeds growing on the surface are buried, where, deprived of sunlight, they should rot down and incorporate organic matter into the soil. Digging, however, is not a fool-proof method of weed control for several reasons. Where there are weeds with perennial underground stems or rootstocks capable of making new growth, eg couch grass, docks or bindweed, turning the soil over is unlikely to kill the weeds. Some weeds, eg groundsel, are still capable of setting seeds even after being buried (although the seeds will not germi­nate until they are brought to the surface at some later stage). Existing weed seeds in the newly exposed soil surface will now be capable of germinating. Also digging near to existing plants is likely to damage their root systems and reduce growth (although where the plants are making rampant vegetative growth, this might encourage flowering). Digging is a useful method for turning over the soil prior to planting and as a way to remove spot weeds, eg docks, but is limited in its value in an established bed or border. Where a perennial weed is present, a propor­tion of the weed’s root or underground system can be removed by forking through the dug soil; this is unlikely to give satisfac­tory control but will reduce the vigour of the weeds and make it easier to control them with a herbicide application to the new growth.

Hoeing involves cutting the weeds off at just below ground level. This can be very effective in dry weather, as the severed tops of the weeds wither and die. However, in wet conditions, the weeds may be able to re-root into the soil. Also, in wet weather it may be difficult to hoe effectively, as the soil may cling to the hoe (stainless steel tools are much better in this respect). The frequent turning over of the top few centimetres of soil will continually expose new weed seeds to the right conditions for germination, and if a prolonged period follows when it is impos­sible or impractical to hoe, a healthy flush of weeds may develop. Hoeing can be a tech­nique useful on bare conditions where perennial weeds are absent and as a thera­peutic form of gardening, combining activity with a useful end product.

A rotovator can be used as a hoe to keep the top few centimetres of the soil loose and friable and to chop up germinating seedlings and established weeds. This can be an effec­tive method of weed control in specific situations where the plants are spaced so that a rotovator can be used between them. As with deep digging, too deep cultivation can restrict plant growth, as will accidental damage to the base of the plants. Using a rotovator is less dependent upon weather conditions than using a hoe, but if the ground is sticky, it can damage the soil structure.

Cutting of weeds is often advocated when establishing woodland. Certainly rampant weed growth can cause the death of plants by competition and by smothering them. How­ever, research shows that cutting weeds, especially grasses, may actually increase the competition they put on the plants; this includes the close mown grass near the base of a tree or shrub. In gardens the weeds should never be allowed to grow rampantly over plants and all plants will do better (newly planted trees and shrubs especially) with an area of at least 60cm (2ft) diameter, preferably 1.2m (4ft), kept free of all compet­ing vegetation. Cutting woody weeds a few days prior to using a herbicide can reduce the quantity of herbicide needed.

Pulling weeds is useful where only the occasional weed is present, on intricate features such as a rockery, or where the weed is about to seed and other methods will entail the release of the seeds. It is often necessary where a weed has established within a plant.