Mulch
A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving fertility and health of the soil, reducing weed growth, and enhancing the visual appeal of the area.
For the community in the United States, see Mulch, Virginia.
A mulch is usually, but not exclusively, organic in nature. It may be permanent (e.g. plastic sheeting) or temporary (e.g. bark chips). It may be applied to bare soil or around existing plants. Mulches of manure and compost will be incorporated naturally into the soil by the activity of worms and other organisms. The process is used both in commercial crop production and in gardening, and when applied correctly, can improve soil productivity.[1]
Living mulches include moss lawns[2][3] and other ground covers.
Uses[edit]
Many materials are used as mulches, which are used to retain soil moisture, regulate soil temperature, suppress weed growth, and for aesthetics.[4] They are applied to the soil surface,[5] around trees, paths, flower beds, to prevent soil erosion on slopes, and in production areas for flower and vegetable crops. Mulch layers are normally 2 inches (5.1 cm) or more deep when applied.[6][7]
Although mulch can be applied around established plants at any time,[8] they may be applied at various times of the year depending on the purpose. Towards the beginning of the growing season, mulches serve initially to warm the soil by helping it retain heat which is otherwise lost during the night. This allows early seeding and transplanting of certain crops, and encourages faster growth. Mulch acts as an insulator. As the season progresses, mulch stabilizes the soil temperature and moisture, and prevents the growing of weeds from seeds.[9]: 768
In temperate climates, the effects of mulches depend upon the time of year in which they are applied. When applied in fall and winter, mulches delay the growth of perennial plants in the spring and prevent growth in winter during warm spells, thus limiting freeze–thaw damage.[10]
The effect of mulch upon soil moisture content is complex. Mulch forms a layer between the soil and the atmosphere reducing evaporation.[11] However, mulch can also prevent water from reaching the soil by absorbing or blocking water from light rains and overly thick layers of mulch can reduce oxygen in the soil.[12]
In order to maximise the benefits of mulch, while minimizing its negative influences, it is often applied in late spring/early summer when soil temperatures have risen sufficiently, but soil moisture content is still relatively high.[13] However, permanent mulch is also widely used and valued for its simplicity, as popularized by author Ruth Stout, who said, "My way is simply to keep a thick mulch of any vegetable matter that rots on both sides of my vegetable and flower garden all year long. As it decays and enriches the soils, I add more."[14]
Anaerobic (sour) mulch[edit]
Organic mulches often smell like freshly cut wood but sometimes they start to smell like vinegar, ammonia, sulfur or silage. This happens when material with ample nitrogen content is not rotated often enough and it forms pockets of increased decomposition. When this occurs, the process may become anaerobic and produce phytotoxic materials in small quantities. Once exposed to the air, the process quickly reverts to an aerobic process, but the anaerobic metabolites may be present for a period of time. Plants low to the ground or freshly planted are the most susceptible, and phytotoxicity from the produced chemicals may prevent germination of some seeds.[39]
On-site production[edit]
Owing to the great bulk of mulch which is often required on a site, it is often impractical and expensive to source and import sufficient mulch materials. An alternative to importing mulch materials is to grow them on site in a "mulch garden" – an area of the site dedicated entirely to the production of mulch which is then transferred to the growing area.[41] Mulch gardens should be sited as close as possible to the growing area so as to facilitate transfer of mulch materials.[41]