Mulch can help deter weeds, prevent surface crusts and minimize surface crusts. Organic mulches include leaves, pine needles, dry grass clippings, compost, crushed bark, or other organic materials. The first mulch option is to simply use organic mulch on the soil surface. Mulch prevents weeds in a number of ways.
New weed seeds need soil to grow, and a thick layer of mulch helps prevent seeds from reaching the soil. As for seeds or roots that are already in the soil, mulch blocks one of the plant's essential needs, sunlight. The weeds will try to break through, but if the layer of mulch is thick enough, it will suppress everything but the toughest one. In addition to throwing away by hand, mulch is probably the most important means of controlling weeds.
However, mulch works best when used as part of a multiple approach in conjunction with pre-emergent herbicides. Mulches can be divided into organic, such as grass clippings, and inorganic, such as black plastic. Mulches may be the easiest and most effective way to control annual weeds in the garden. Mulches can also suppress perennial weeds.
Mulches control weeds by preventing sunlight from reaching the soil surface. Light is required for the germination of certain weeds and light for the growth of all green plants. Organic mulches provide good annual weed control, but perennial weeds can get through the mulch layer. In most gardens, annual weeds can be controlled by a combination of mulching and weeding by hand, and herbicides are not needed.
If weeds are initially controlled by other means, competition between crops will reduce weed growth once vegetables are well established. Transparent plastic, which increases soil temperature more than black plastic, does not control weeds, since sunlight can reach the soil surface. Bark mulch is the best choice for use as a weed suppressant because it inhibits weeds in two fundamental ways. To stop weeds in mulch with pre-emerging herbicides, start by raking the mulch to the side and then mow or cut existing weeds.
Annual grasses are easy to control if appropriate measures are taken early in the growing season, but they can quickly become a serious problem if left uncontrolled when they are small. Broadleaf weeds with small seeds, such as pigweed, are easier to control than broadleaf weeds with large seeds, such as Morningglory. Research generally indicates good annual weed control, but annual weeds can germinate above the tissue and send their roots through the tissue. Weed control is one of the main reasons for applying mulch, but annoying weeds can persist, even if a layer of bark chips or pine needles is carefully applied.
When used correctly before weeds sprout in early spring, pre-emerging herbicides are an effective way to prevent weeds from accumulating in mulch. If you haven't applied mulch yet, gardening fabric or weed control cloth are a safe way to block weeds and, at the same time, allow water to pass into the soil. Early season weed control will greatly reduce the time needed to weed by hand later in the growing season.