How to weed control? Weeds are plants growing where they are not wanted. Usually they are native plants that grow successfully in the wild, but quite often they may be cultivated plants invading new areas.
Some weeds are not only attractive but may also have beneficial effects. Scarlet pimpernel (Anagallis arvensis) and wild pansy (Viola tricolor) bear attractive flowers, cow parsley (Anthriscus sylvestris) supports beneficial hoverflies, and red dead nettle (Lamium purpureum) attracts bees.
It hardly needs saying that wild plants should be tolerated and indeed actively nurtured in appropriate places near the kitchen garden. Crops will, however, be adversely affected by weed competition, and for most people a weed-free garden is more attractive than one left to its natural development.
Weeds can be divided into two groups for the purposes of control: perennial weeds and annual weeds.
HOW WEEDS AFFECT CROPS
By far the worst effects of weeds lie in competition. Weeds absorb water and nutrients from the soil, depriving crop plants and so restricting their growth. They compete for light, and vigorous weed growth can seriously shade young developing plants.
They also compete for space, which may result in restricted or stunted growth of cultivated plants. Weeds can also affect pest and disease incidence.
Some weeds may harbor pests such as eelworm and diseases such as clubroot of brassicas or rusts, these being found in weed plants closely related to cultivated crop species.
Dense weed growth may become soaked by rain, reducing air movement and increasing humidity around plants, providing ideal conditions for diseases such as botrytis, which affects the fruits of strawberries. Heavy weed growth looks unsightly and can make harvesting more difficult; pulling vegetables that are surrounded by nettle growth can be painful.
Another effect worth noting, although of very limited importance, is that some weeds may exude chemical substances at root level that have the effect of restricting the growth of non-related plants.
Potentially most troublesome weeds are those perennials that increase primarily by vegetative means, such as spreading roots or runners or rooting stem tips, rather than by seed production.
These weeds are of particular concern on un-cropped sites where they have become well established; they are also potentially troublesome where they spring up among newly sown or planted fruit and vegetable crops and are then very difficult to eradicate without disturbing the crop.
Notorious perennials are curly dock (Rumex species), dandelions (Taraxacum officinale), stinging nettle (Urtica dioica), creeping buttercup (Ranunculus repens), ground elder (Aegopodium podagraria), couch grass (Agropyron repens), brambles (Rubus species), and horsetail (Equisetum species).
A new site in which such weeds are well established can be daunting, but it is essential to clear out any of these inhabitants and destroy early any small colonies within already cultivated plots.
Nonwoody perennials can be controlled by long-term covering with heavy-gauge black film plastic or other durable, light-excluding material such as old carpet. To be most effective it will need to be in place for at least a whole growing season, so forward planning is essential.
Lift the cover occasionally and carefully dig out any struggling weeds. The more usual method is to cultivate the ground with a shovel or fork. Break open the ground to a spit depth, and shake or pick out by hand tuberous or woody roots or underground runners.
This is best done on hot days, leaving weeds exposed for a while to be desiccated and killed; then dispose of them off-site. It is unlikely that one session will clear the land, because many of the weeds will regenerate from even the smallest fragment, so be prepared to repeat the task.
Using a mechanical rotary cultivator to chop up the existing ground cover is less advisable. It is effective only with many repeat operations, because underground weed parts are chopped into pieces, each of which will regenerate. Worst of all, it can destroy the soil structure and produce an impermeable soil pan (see p.16) at the depth of the spinning blades.
The persistence of perennial weeds varies. Curly dock, dandelions, and creeping buttercup soon succumb to careful cultivation, but couch grass and stinging nettles require careful and repeated lifting. Worst of all are horsetails, which may be very deeprooted and impossible to eradicate
The armed stems of brambles are formidable, but they can be removed with methodical use of pruners and a shovel. Bulbous perennials, such as a few Oxalis species or ramsons (Allium ursinum), call for meticulous lifting or constant removal of leaves to weaken the plant.
Fortunately, these attractive weeds are less competitive than many, but in high density they can still smother other plants.
Chemical weedkillers can be a great help in preparing new ground, in controlling persistent or deeply established perennial weeds, and where weeds invade from adjoining land. Their use is a matter of imposed as well as personal choice, since the range is narrowed due to legal restrictions on manufacture.
There is no real risk to personal safety if the instructions are followed to the letter, but valued plants are vulnerable to drift or careless use of weedkiller. Important rules are: keep a marked watering can or sprayer solely for weedkiller; choose the appropriate material; mix and apply it with great care, preferably on a still day—a dribble bar can be useful; and place physical barriers around any crop plants in the immediate area.
The chemical glyphosate is highly effective; it will be absorbed into actively growing plants. There are also chemicals specifically for perennial grasses and hormone weedkillers for persistent weeds like brambles and bindweed (Convolvulus arvensis).
The latter can be painted on to aerial parts of plants. Inspect the shelves of a well-stocked garden center and spend a while making a careful selection. Bear in mind that many perennial weeds are also prolific seeders, including curly dock and dandelion.
Annual weeds complete their life cycle in one season; there may even be more than one life cycle per season. There are a few significant biennial weed plants, which make growth in one season and flower in the following one, and these may be regarded as annuals.
By and large annuals are more readily controlled than perennials. The group includes chickweed (Stellaria media), groundsel (Senecio vulgaris), annual meadow grass (Poa annua), goosefoot (Chenopodium album), hairy bittercress (Cardamine hirsuta), speedwell (Veronica species), and annual nettle (Urtica urens). These weeds reproduce through the prolific production of seeds, making up a large part of the estimated 100,000 seeds in each square yard (square meter) of soil.
Many seeds are lost to the predations of birds and soil-inhabiting creatures, while others fail to develop after germination. Cultivating will destroy many, but moves dormant seeds to conditions favorable to germination. Destroy all flowering weeds before they have chance to set seed.
Regular hoeing is the most effective means of controlling annuals, since severed parts do not regenerate. Hoe as soon as the crop rows can be identified, and repeat frequently. Work shallowly to avoid bringing more seeds to the surface and to minimize soil moisture loss. It is most important to hoe between crop rows.
Hand weeding is a quite satisfying pastime in the control of annual weeds. A flame gun can be used on pathways, but it is a specialized tool rather than an essential. A valuable technique for suppressing seeding weeds is the stale seedbed practice of allowing a flush of weeds to grow on a prepared bed, and then destroying them by shallow hoeing or with a flame gun before sowing.