In agriculture and gardening, mulch is a protective cover placed over the soil, primarily to modify the effects of the local climate. A wide variety of natural and synthetic materials are used. Mulching is an important part of any no-dig gardening regime, such as practiced within permaculture systems.
The mulched area should include as much of the root zone as possible, For flower beds mulch the entire area. For individual plants, such as trees, the mulched area should extend at least 3 to 6 feet out from the base of the plant. It is advisable to pull the mulch 1 to 2 inches from the base of plants to prevent bark decay.
Mulch can be applied any time of the year. However, the best time to mulch is late spring after the soil has warmed. Early spring application will delay soil warming and possibly plant growth. It is not necessary to remove the mulch when you fertilize. Apply the fertilizer over the mulch—nutrients will move with water to the roots below.
Mulching trees and shrubs is a good method to reduce landscape maintenance and keep plants healthy. Mulch helps conserve moisture—10 %to 25% reduction in soil moisture loss from evaporation. Mulches help keep the soil well aerated by reducing soil compaction that results when raindrops hit the soil.
Mulches prevent soil and possible fungi from splashing on the foliage—thus reducing the likelihood of soil-borne diseases. They help maintain a more uniform soil temperature (warmer in the winter and cooler in the summer) and promote the growth of soil microorganisms and earthworms. They also reduce water runoff and soil erosion.
Mulches eliminate mowing around trees and shrubs and provide a physical barrier that prevents damage from lawn mowers and weed trimmers. A 2- to 4-inch layer (after settling) is adequate to prevent most weed seeds from germinating. Mulch should be applied to a weed-free soil surface. Simply covering perennial weeds such as bermudagrass or nutsedge will not prevent their growth.
There are a number of materials that can be used for mulching, and each has its own advantages and disadvantages.
Organic Mulch Materials
Many organic materials can be used as mulch. The material should be weed-free, non-matting, easy to apply and readily available. Fine particle organic mulch will form a more complete soil cover than a coarse, loose material. Coarse mulch material will need to be applied thicker in order to achieve the desired benefits.
Organic mulches decompose with time, releasing small amounts of nutrients and organic matter to the soil. The layer of mulch should be renewed as needed to maintain a 2- to 4-inch depth. On previously mulched areas, apply a 1-inch layer of new material. Pine straw will need to be reapplied each year while pine bark may not need to be replenished for several years.
Some of the best organic materials include pine bark nuggets, pine straw and compost. Pine straw is aesthetically pleasing and will remain in place better than most other materials. Pine bark nuggets are longer lasting, but can be washed with a heavy rain.
Mulch made from straw is generally lighter and easier to use than bark mulches, with the added advantages of being biodegradable and neutral in pH. Straw mulch tends to additionally have higher moisture retention and weed controlling properties than other mulches.
Yard waste, such as grass clippings, leaves and small twigs can be used as mulch in moderation. The back side of the shrub border or natural area is an ideal place to dispose of small pruning clippings. Ideally, these materials should be shredded or composted before applying; however, small amounts can be applied to existing mulch.
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 germinating weed seed.
Plastic mulch used in large scale commercial production is laid down with a tractor-drawn or standalone plastic mulch layer. 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.
Mulch should normally smell like freshly cut wood, but sometimes will develop a toxicity that will cause it to smell like vinegar, ammonia, sulfur or silage. This happens if the material is not rotated often enough and it forms pockets where no air is circulating.
When this occurs, the decomposition process become anaerobic and produces these toxic materials in small quantities. Once exposed to the air, the process quickly reverts to an aerobic decomposition, but these toxic materials will be present for a period of time.
Anaerobic decomposition is often a problem with leaves or large piles of wood chips. Such materials are toxic to plants due to the byproducts of anaerobic decomposition: methane and alcohol. The mulch will have a smell of vinegar, ammonia or sulfur. Marginal leaf chlorosis, leaf scorch, defoliation and/or plant death may occur. Damage usually occurs within twenty-four hours after application.
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