Weeds are the bane of gardening life. Left on their own, they out compete crops for water, light and fertility, often leaving the less fastidious gardener with little to harvest. Because they prefer undisturbed soil, biennial weeds are seldom a problem in a vegetable garden. The main culprits are the annual and perennial weeds, and they more than make up for the absence of their compatriot.
Annual weeds, such as fat hen and chickweed, constantly regenerate from seed reserves in the soil. The population in the reserves is often huge, the result of past years’ negligence in removing weeds before they flower and shed their seeds. These seeds, though alive, are dormant, and can remain in this state for years. Disturbing the soil by digging or hoeing breaks the dormancy of some of them, and a mob of weed seedlings suddenly emerges. The remaining seeds stay dormant, patiently biding their time until their turn comes to germinate.
Every effort should be made to prevent fresh seed from replenishing the numbers already there. Easier said than done, it means scrupulously removing all weeds before they shed seed, and using only weed seed-free organic matter for mulching and soil improvements.
Annual weeds should be controlled when they are still seedlings and before they compete with the crops. Rotations and mulches are powerful allies in the fight against annual weeds, but to be most effective they need to assisted by other techniques.
Hoeing and hand weeding
Hoeing and hand weeding are vital in the fight against weeds. They are the perfect partners that complement each other in a vegetable and herb garden.
Hoes consist of broad metal blades dragged or pushed between crop plants so that they cut the weeds off at ground level. Where there is enough space between plants they are an efficient means of controlling weeds.
Promoting crop competition
The crops themselves can be managed to improve their ability to fight weeds. They can, for example, be transplanted or grown at equal spacings in order to smother weeds and keep their growth in check. In addition, poor competitors like onions can be kept off weedy ground, substituting instead a strong competitor like chards.
Using stale seedbeds
Stale seed beds are used to give crop plants a head start over weeds. The bed is prepared a week or two before sowing to allow the weed seeds stimulated by the soil disturbance to germinate. The seedlings are then hoed off, producing what is called a “stale seedbed”, where the remaining weed seeds are still dormant.
Perennial weeds come back year after year from hardy roots and stems that remain in the soil, enduring both dry summers and cold winters. Some, like docks and dandelions, have deep taproots, while others, such as couch grass and stinging nettles, have a system of creeping roots or stems that spread in the soil throughout the plot.
Since they are masters of survival, perennial weeds are difficult to eradicate once they become established. Digging can get rid of them, but this is a tedious and time-consuming job that needs to be done thoroughly since new plants can regenerate from any pieces left behind.
Hoeing their above ground growth brings temporary respite, and theoretically weakens the plants resulting in death if done often enough. In practice, though, eradication by hoeing is very difficult since the tops need to be removed regularly and frequently – one could say fanatically – for several years.
Perennial weeds can also be controlled by mulches laid between the crop plants. There are several types of mulches, ranging from old carpets and black plastic to wood chips and other inert organic matter. Perennial weeds will grow though the wood chips, but will not be able to do anything about black plastic mulches.
Many of perennials, such as docks, produce seed from which new plants can grow. Like annuals, they should never be allowed to flower and set seed in the garden. Some perennials, like dandelions, can blow in from scrub ground or abandoned plots, and there is little or nothing that can be done about it.
If the fight against perennial weeds is being lost, then the affected parts of the garden can be surrendered and covered with a black plastic film. After 2 or 3 years in the dark, the weeds underneath should have been killed, rescuing the area for future vegetable and herb production.
Covering the soil with a layer of material is called ‘mulching’. A wide range of materials, such as old carpets, newspapers and lawn clippings, can be used as a mulches.
In a vegetable and herb garden, mulches are at their best nestled among the plants, where they check the growth of weeds, reduce water evaporation from the soil surface and promote earthworm activity. The soil underneath a mulch is also protected from the ravages of heavy rains and insulated against temperature extremes.
The temperature and moisture level of a mulched soil are slow to change, so mulches should be put down only when the soil is warm and moist. Unfortunately, slugs and snails love the moist environment underneath a mulch, and crop losses can be catastrophic if their populations build up. The advantages of mulching, however, far outweigh the disadvantages, and they should be used whenever possible.
Bulky organic materials such as compost are a natural choice for mulching home gardens. They not only add organic matter to the soil, but many of them are also a source of plant nutrients. Most, too, come from recycled garden and kitchen wastes and cost nothing to make.
Organic mulching material should be weed-free and loose enough for air and water to pass through to the soil underneath. If wood shavings and saw dust are used, they must come from untreated wood, otherwise the soil will be contaminated. To avoid them depleting the soil of nitrogen, they also need to be weathered in the open for a couple of years before being used.
Bulky organic mulches should be spread thickly enough to do their job, but not so thick as to cover the crop plants. To some extent, ‘thicker is better’, though the ideal thickness varies with several factors, including the type of crop, the material being used, and the quantities of mulch that are available.
Many gardening catalogues and nurseries sell opaque plastic films that are custom-made for mulching. The films are petroleum-based products and are very effective in controlling both annual and perennial weeds.
Cash-strapped gardeners and those concerned with the use of a non-renewable resource can try getting their plastic mulch from local dairy farmers. The farmers often use large sheets of black plastic to cover their silage, and periodically replace them as they wear out. Usually, though, the plastic still has some life left in it, and there are often pieces big enough to cover a vegetable or herb bed.
The plastic is normally laid over a bed before the crop is sown or transplanted. It is held down by soil stacked along its edges, and the holes for the plants are cut either before or after it is laid. Sowing, planting and watering are done through the holes, which will need to be weeded until the crops get big enough to compete on their own.