Definition
In agriculture and gardening, mulch is a protective cover placed over the soil, primarily to modify the effects of the local climate.
Basics
A wide variety of natural and synthetic materials are used. Materials used as mulches vary and depend on a number of factors. Use takes into consideration availability, cost, appearance, the effect it has on the soil - including chemical reactions and pH, durability, combustibility, rate of decomposition, how clean it is - some can contain weed seeds or plant pathogens.
A variety of materials are used as mulch:
- Organic residues: grass clippings, leaves, hay, straw, comfrey, shredded bark, whole bark nuggets, sawdust, shells, wood chips, shredded newspaper, cardboard, wool, but also manure (cow), etc. Many of these materials also act as a direct composting system, such as the mulched clippings of a mulching lawn mower, or other organics applied as sheet composting.
- Compost: This should be fully composted material to avoid possible phytotoxicity problems, and the weed seed must have been eliminated, otherwise the mulch will actually produce weed cover.
- Rubber mulch: made from recycled tire rubber.
- Plastic mulch: crops grow through slits or holes in thin plastic sheeting. This method is predominant in large-scale vegetable growing, with millions of acres cultivated under plastic mulch worldwide each year (disposal of plastic mulch is cited as an environmental problem).
- Rock and gravel can also be used as a mulch. In cooler climates the heat retained by rocks may extend the growing season.
Application: Mulch is usually applied towards the beginning of the growing season, and may be reapplied as necessary. It serves initially to warm the soil by helping it retain heat. This allows early seeding and transplanting of certain crops, and encourages faster growth. As the season progresses, the mulch stabilizes temperature and moisture, and prevents sunlight from supporting germinated weed seed.
Plastic mulch used in large-scale commercial production is laid down with a tractor-drawn or standalone layer of plastic mulch. This is usually part of a sophisticated mechanical process, where raised beds are formed, plastic is rolled out on top, and seedlings are transplanted through it. Drip irrigation is often required, with drip tape laid under the plastic, as plastic mulch is impermeable to water.
In home gardens and smaller farming operations, organic mulch is usually spread by hand around emerged plants. For materials like straw and hay, a shredder may be used to chop up the material. Organic mulches are usually piled quite high, six inches (152 mm) or more, and settle over the season.
In some areas of the United States, such as central Pennsylvania and northern California, mulch is often referred to as "tanbark", even by manufacturers and distributors. In these areas, the word "mulch" is used specifically to refer to very fine tanbark or peat moss.
Mulch made with wood can contain or feed termites, so care must be taken about not placing mulch too close to houses or building that can be damaged by those insects. Some mulch manufacturers recommend putting mulch several inches away from buildings
Sour mulch Mulch should normally smell like freshly cut wood, but sometimes develops a toxicity that causes it 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 these phytotoxic materials in small quantities. Once exposed to the air, the process quickly reverts to an aerobic process, but these toxic materials may be present for a period of time. If the mulch is placed around plants before the toxicity has had a chance to dissipate, then the plants could very likely be damaged or killed depending on their hardiness. Plants that are predominantly low to the ground or freshly planted are the most susceptible, and the phytotoxicity may prevent germination of some seeds.
If sour mulch is applied and there is plant kill, the best thing to do is to water the mulch heavily. Water dissipates the chemicals faster and refreshes the plants. Removing the offending mulch may have little effect, because by the time plant kill is noticed, most of the toxicity is already dissipated. While testing after plant kill will not likely turn up anything, a simple pH check may reveal high acidity, in the range of 3.8 to 5.6 instead of the normal range of 6.0 to 7.2. Finally, placing a bit of the offending mulch around another plant to check for plant kill will verify if the toxicity has departed. If the new plant is also killed, then sour mulch is probably not the problem.
Living mulches are plants sown to grow close to the ground, under the main crop, to slow the development of weeds and provide other benefits of mulch. They are usually fast-growing plants that continue growing with the main crops. By contrast, cover crops are incorporated into the soil or killed with herbicides. However, living mulches too may need to be mechanically or chemically killed eventually to prevent competition with the main crop (Brandsaeter et al. 1998, Tharp and Kells, 2001).
Topics of Interest
Rubber mulch is a type of mulch that is made from 100% recycled rubber.
Rubber mulch provides several advantages over plant material based mulches. For landscaping and gardening purposes, both nuggets and buffings insulate soil from heat allowing a 2 or 3 degrees F higher soil temperature difference over wood mulches. Rubber mulch is beneficial for soil moisture as rubber is non-porous and does not absorb water on its way through to the soil. It also reduces fungus growth and plant growth, and becomes a weed barrier as weed seeds dehydrate in the mulch before reaching the soil. Neither nuggets nor buffings provide any humus to compacted soil types.
Disadvantages: Some recycled varieties may leach chemicals(some toxic) which are harmful to plants. Rubber mulch, like some organic mulches, is a hazard if ignited. However, rubber mulch is more difficult to extinguish. Although rubber mulch is generally safe, recycled tire rubber leachates do contain certain minerals and compounds which may cause concern in high concentrations. Recycled tire mulch can contain trace amounts of various minerals from the tire manufacturing process and other chemicals that may have been picked up during the tire's service life.
Plastic mulch is a product used, in a similar fashion to mulch, to suppress weeds and conserve water in crop production and landscaping. Certain plastic mulches also act as a barrier to keep methyl bromide, both a powerful fumigant and ozone depleter, in the soil. Crops grow through slits or holes in thin plastic sheeting. Plastic mulch is often used in conjunction with drip irrigation. Some research has been done using different colors of mulch to affect crop growth. This method is predominant in large-scale vegetable growing, with millions of acres cultivated under plastic mulch worldwide each year. Disposal of plastic mulch is cited as an environmental problem, however, technologies exist to provide for the recycling of used/disposed plastic mulch into viable plastic resins for re-use in the plastics manufacturing industry.
In agriculture, gardening, and landscaping, barkdust (also bark dust, bark chips, bark mulch, or beauty bark) is a form of mulch produced out of chipped or shredded tree bark. Coarser forms of barkdust may be known as bark nuggets. Trees typically used in the production of barkdust include the Douglas fir and the Western hemlock.
Hydroseeding (or hydraulic mulch seeding, hydro-mulching, hydraseeding) is a planting process which utilizes a slurry of seed and mulch. The slurry is transported in a tank, either truck- or trailer-mounted and sprayed over prepared ground in a uniform layer. Helicopters may be used in cases where larger areas must be covered. Aircraft application may also be used on burned wilderness areas after a fire, and in such uses may contain only soil stabilizer to avoid introducing non-native plant species. Hydroseeding is an alternative to the traditional process of broadcasting or sowing dry seed. It promotes quick germination and inhibits soil erosion.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)
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