Organic weed control in lawns concentrates on encouraging the grass to grow well, as a vigorous dense sward will overcome the weeds.
However, a lawn does not have to consist entirely of grass. Unless you are trying to reproduce a cricket wicket or a putting green, some weeds can even be desirable as they can help the lawn resist wear and stay green. Clover, for example, feeds the lawn with nitrogen produced by its root bacteria, and yarrow keeps green under dry conditions. The varied leaf shapes and textures and a few flowers from daisies, bird’s-foot trefoil and selfheal can add to rather than detract from a lawn’s appearance. Nevertheless, weeds must be prevented from getting out of hand.
The first principle of lawn weed control is therefore to make sure that conditions are suitable for grass to grow. There are many weeds that do better than grass in very shady situations or wet places, or where the soil is compact. If you cannot correct the conditions, grow another ground cover plant that will tolerate them. However, be wary of using invasive species as these can become weeds themselves. Alternatively, where appropriate, lay a hard path, paving or gravel instead of grass.
On an established lawn, encourage the grass to grow strongly and healthily by cutting it regularly but not too closely, and liming if necessary. Leave the mowings on the lawn except in cold, wet conditions, as the mowings will feed the lawn and encourage worm activity.
Remove weeds such as dandelions and plantain which have large, flat leaves. This is because the foliage tends to smother the grass. In an organic garden this has to be done by hand: loosen them with a garden fork and pull them out, or cut them out with an old kitchen knife. Special lawn-weeding tools are also available, however. They are particularly useful because they enable you to remove weeds along with a plug of soil without getting down on your hands and knees.