Not all mulching is the same
The concept of mulching can sometimes be misunderstood. In some cases it can be seen to refer to mulching a lawn or alternatively it could refer to spreading clippings over garden beds. Both refer to different areas of gardening. They do have some aspects in common.
The origins of the word "mulch" sheds some light. Its origins refer to a covering of straw or compost. In farming and gardening, mulching typically refers to spreading shredded plants or other materials over the soil as a loose top layer. Lawn mulching is actually very similar as finely shredded plant cuttings are spread over the grass. A good mulching lawn mower accomplishes three tasks at the same time: it cuts the grass, shreds the clippings and immediately spreads them over the lawn. If you have vegetable beds as well as lawns, you should regularly spread some of the clippings on these beds, too. The ideal mulch is dried clippings, spread in a thin layer to a maximum two centimetres. If the clippings are too fresh or dense, they may begin to turn mouldy. This should not be allowed to happen as mould would be harmful to vegetable plants.
What are the advantages of mulch in vegetable beds? Mulch shades the ground, considerably reducing evaporation, saving you a great deal of watering in summer. Water stays where it belongs, at the roots of the plants as the mulched soil stays moist; it is also full of life. Earthworms and other soil organisms keep the soil loose. Earthworms pull the blades of grass into the soil to eat them, leaving behind "black gold": worm castings or humus, the best organic fertiliser in the world. This way, the mulch layer also fertilises the beds. In summer, a thin layer of mulch "disappears" within four to five weeks. This means it has already become valuable fertiliser for the vegetables. Another advantage of mulching is that the surface of the soil cannot turn to mud when it rains and so the soil is not compressed. Finally, the mulch hinders the growth of weeds reducing time spent weeding.
What are good mulching materials? (Dried) clippings are an ideal mulching material, as is hay (as long as the seeds are unripe), and also finely shredded stinging nettles or comfrey leaves. Bark mulch is unsuitable for vegetables and should only be spread over paths or around shrubs and bushes. Caution is also advised when mulching with flax or straw, as they do not contain much nitrogen and so, as they decompose, draw nitrogen out of the soil and out of the plants. For perennial herbs, bushes and shrubs, mineral substrates such as gravel, lava stones and pumice stones are also suitable and can also be used for containers. Sifted compost residues and bark mulch are particularly suitable as a mulching layer for berry bushes and fruit trees.
Left: unmulched, compressed soil. Right: mulched soil. The layer of mulch keeps the moisture in the soil, keeps the rain in check and allows water to seep slowly into the ground.
The soil beneath the layer of mulch is loose and allows roots to penetrate easily.