Preventing Weeds
The best way to control weeds in your garden is to prevent them from establishing in the first place. There are a number of ways to do this, all of which will reduce the need for weeding later on in the season.
1. Clearing the Soil
Before planting, always make sure that you have cleared the site of all annual and perennial weeds. This may be done chemically or by hand. If your site is overrun with perennial weeds, treat the whole area with a weedkiller the season before planting. The odd perennial weed may be simply removed the winter before planting using a garden fork. Eradicate annual weeds by spraying or by forking out before planting.
It may be possible to treat soil that has been overrun by perennial weeds by laying a carpet or light-excluding black polythene over the site, and leaving it undisturbed for at least two years. This can starve out perennial weeds, however extensive their root systems.
Avoid disturbing the soil unnecessarily, as this may bring dormant weed seeds to the surface where they can germinate.
2. Keeping Plants Healthy
Always bear in mind that strong, vigorous plants will be able to compete with weeds much more effectively than ones that are weak or struggling. Healthy plants that form a lush, leafy canopy will also discourage weeds from establishing beneath their spreading foliage.
3. Mulching
Adding a mulch layer around plants blocks out light, preventing weed seeds from germinating. To be totally effective, organic mulches need to be 10 cm (8 in) thick. However, although thinner layers (5 cm/2 in) may allow the occasional perennial weed to grow through, they often root in the mulch itself, and so are easy to remove. Avoid using garden compost or manure, as this often contains weed seeds; use leaf mould, peat substitute or processed bark instead.
Inorganic mulches tend to be more effective at suppressing weed growth; a layer of black plastic sheeting will prevent annual weeds from establishing, and may also stop the growth of perennials. Crops and other plants may be grown through the mulch by simply cutting a cross in the plastic and positioning desirable specimens through it. The unattractive plastic surface may be concealed with a layer of bark or gravel.
4. Planting Ground Cover
There are a number of ground cover plants such as periwinkle (Vinca) and lady's mantle (Alchemilla mollis) that will grow in dense carpets and suppress the germination of weed seeds. Plant them in weed-free soil to ensure that they are given a good head start.
5. Companion Planting
Some vegetable crops are known to help suppress or clear the ground of weeds. For example, sowing turnips has been shown to inhibit the growth of horsetail shoots, possibly due to an inhibiting substance produced by the turnip; this would need to be done for a few seasons to exhaust the rhizomes. Potatoes compete well with annual weeds and may be grown to help retain weed-free ground for subsequent planting.