Mulch is a protective covering placed over the garden soil and is mainly used to keep weeds out and moisture in. There are many advantages to using mulch in your vegetable garden. When added to a garden shortly after seeds germinate, it prevents weeds from growing by depriving them of sunlight.
If weeds are not controlled, they compete aggressively with the vegetables in your garden for water, sunlight, and space. Mulches attract our friends the earthworms to the soil, which provides the soil with more nutrients. Mulch also provides insulation, keeping the soil at a relatively uniform temperature. This allows for harvesting root crops well into November in colder regions. Because mulch insulates the soil, it also reduces the evaporation of water from the surface of the soil. Mulch reduces erosion and helps to keep the soil from becoming packed as well as keeps your vegetables clean.
Before applying any mulch to your garden, be sure the garden is weeded and the soil is broken up and moist. It is best to mulch after the garden has been watered to encourage moisture to stay in the soil. In general, mulch is easy to apply, and well worth the effort. Once seeds have germinated or transplants are set out, spread mulch between the rows being careful not to cover the plants. Mulch layers must be thick enough to be effective which depends on the type of mulch you are using. (See below) When choosing a type of mulch, use whatever is cheap and readily available in your area.
Organic Mulches
- Bagasse – Baled crushed sugar cane, a by-product of sugar manufacturing, can be used as mulch where available. It has great water-holding capacity, and should be applied 2-3 inches thick.
- Bark chips – The bark of coniferous trees, is available in sizes from a small nugget to a finer grade. They make an attractive covering that permits easy penetration of rainwater.
- Buckwheat hulls – A lightweight mulch, high in potash, with a warm brown color that is attractive and does not mat. This lasts for 1 to 2 years and does not decompose quickly. Spread at least 2 inches deep. More practical for ornamental plantings, such as rose beds.
- Cocoa bean shells – Similar in quality to buckwheat hulls, these have a decidedly chocolate odor, especially on a warm summer day, that some may find objectionable. The odor wears off in time. Spread at least 2 inches thick. More practical for ornamental shrub borders.
- Coffee Grounds – Used lightly, these can be quite effective. If applied too thickly without being worked into the soil, they may mat and sour. Slightly acidic, if used frequently, add a dusting of lime to the soil where applied.
- Compost – The most widely used mulch material, free for the making and highly beneficial to the soil. Spread at least 2 to 3 inches thick.
- Corncobs (ground) – Ground to a rough texture, corncobs are an excellent, inexpensive mulch material that will eventually decay and add nutrients to the soil. Spread at least 3 inches thick. Because their decomposition requires nitrogen-consuming bacteria, add nitrogen fertilizers, such as cottonseed meal or ammonium sulfate to the soil at the same time.
- Cornstalks (chopped) – If chopped, cornstalks can be used as a late mulch for fall crops, but nitrogen fertilizers must be added to control the nitrogen balance in the soil.
- Grass clippings – An excellent source of nitrogen, used in moderation. For best results, cultivate a layer of 1 or 2 inches into the top of the soil to initiate decomposition. Grass clippings left on the surface mat, cause a bad odor, and form an impenetrable blanket that blocks out the rainfall.
- Leaves – Fall leaves are excellent soil improvers, but tend to blow and decompose slowly if not incorporated into a compost pile. They should be used as a light mulch; thick layers mat and block out rain. Leaves are handiest for mulch if put through a shredder.
- Manures – When there is abundant supply, manures are sometimes used as top mulches. They are best worked into the soil at planting time, where they will do more good.
- Newspapers – An excellent, inexpensive, biodegradable mulch. Approximately 10 overlapping sheets can be put in thick layers, watered down, and weighted with rocks and soil. Though unattractive, newspapers can be covered lightly with other mulch materials to make the garden more appealing. They completely block weed growth. The question of lead leaching into the soil from the newsprint ink has been researched by soil scientists, and their findings show that only negligible amounts leach into the soil, and there is little danger of contamination. However, glossy magazine paper printed with colored inks have high levels of lead and are not recommended for garden mulch.
In addition, lead was banned as an ingredient in ink by the EPA in 1985 and is, therefore, no longer a threat…Ingestion of inks used on newsprint has not been an issue because the ingredients used in the inks are not considered toxic in either the liquid or dry state. - Peanut shells – Where available locally, these are lightweight and high in nitrogen. Apply 2 -3 inches thick.
- Peat moss – Although it is attractive, this light, fluffy soil improving product either mats or becomes too light and fluffy to be an effective mulch. It absorbs moisture much needed by the soil, depriving the soil. It is better as a soil improver worked into the ground during preparation for planting.
- Pine needles – usually recommended for acid-loving shrubbery, such as azaleas and rhododendrons, although they do not alter the soil pH, these can be used on the vegetable garden if in great surplus. Strawberry growers especially prefer them.
- Salt hay – Where available, this is an excellent vegetable garden mulch that can be used for several years, as it decomposes slowly. Be sure the mulch is thick enough, 3-6 inches are needed to be effective. Excellent for melons, cucumbers, and unstaked tomatoes, to keep the fruit clean.
- Seaweed – This has been used successfully on seaside gardens with a negligible effect of leached salts. The materials are high in potash. If worked well into the soil it will provide an excellent source of organic matter.
- Spoiled hay – This is hay not fit for stock feed, and usually inexpensive (dealers like to dispose of it). Use as a mulch year-round or spread after the garden has been planted. Apply at least 3 to 6 inches thick. Sometimes hay is a source of weeds to the vegetable garden, depending on when the hay fields were mowed.
- Straw – Another excellent mulch material. As with the other high-carbon mulch materials, add nitrogen fertilizers to replace the nitrogen depletion caused by bacterial action.
- Tea leaves – A fine mulch, high in nitrogen. Work lightly into the soil surface.
- Tobacco stems – High in potash, these may do more harm than good, since they probably carry mosaic virus. Their nicotine content may have some insecticidal value, but may also affect soil bacteria and earthworms.
- Wood chips – Where plentiful near mills and so forth, these are an excellent mulch and can be used freely, but again watch out for nitrogen loss and compensate.
Inorganic Mulches:
- Stones/Gravel – These are semi-permanent mulches. They have some decorative qualities, but are not recommended for vegetable gardens, except maybe pot gardens on patios and penthouses. They do keep the soil cool and keep the moisture in.
- Black plastic mulch – This remarkable innovation in raising vegetables has proved to be a great labor saver and booster for larger and earlier crops. Although it is not especially attractive to see when laid out between garden rows, it is extremely effective.
Plastic mulch is particularly recommended for crops that have trailing plants with fruit on the ground such as melons, cucumbers, squash, and tomatoes. It is also great for eggplants and peppers. Plastic keeps the fruit clean and overcomes the weeds effectively. The mulch is made of black polyethylene film (1 1/2 mil), and is readily available at garden centers or from mail-ordered catalogs. Colored mulch such as painted plastic, may have other benefits as well; among them raising yields and deterring specific insects. In South Carolina, red mulch increased yields of cowpeas as much as 12 percent over the yields achieved with white or black mulch. Red is also believed to increase tomato yields, particularly early in the season, but has also been found to attract some pests. Orange mulch repels sweet potato whitefly but may attract other pests. Studies at the University of Florida have shown that of all the available colors, red attracts the most whiteflies, blue attracts the most aphids and thrips and white aluminum is the least attractive to all three pests.
Although plastic mulch appears to be a smothering cover over the soil that would deter plant growth, continual use of plastic in field and garden tests have shown that the mulch has many benefits. Plastic mulch controls weeds, raises the soil temperature, reduces loss of moisture, enhances bacterial activity in the soil, provides better aeration, reduces fertilizer leaching, keeps fruits and vegetables clean and improves growth rate. Plants grow faster because mulch is impermeable to carbon dioxide. Because of this, high levels of carbon dioxide build-up under the plastic, escaping through the planting holes and resulting in a high concentration of carbon dioxide around the base of the plants, encouraging growth.
Unlike other mulches, plastic mulch must be laid before the plants are in the garden. Be sure to prepare your garden soil properly and water the garden before laying plastic mulch. Because plastic is very light, it’s best to lay it on a calm day. Use soil or rocks to anchor the edges of the plastic. For best weed control, be sure to overlap the plastic when laying a piece for the next row. Once it’s in place, cut holes in the plastic just large enough for the roots of your plants using a trowel, bulb planter, or opened can. Insert the plant into the soil through the hole in the plastic and pack the soil tightly around the roots. Mound the soil around the hole on top of the plastic to keep the wind from catching it. Cut a small slit in the plastic in between each plant to allow for rain penetration. For seeded crops like corn or onions, wait until the seedlings have grown to about 3 inches high and then lay the plastic down in strips between the rows.
Once your harvest is complete, the plastic can be saved for the following year. Roll it neatly onto an old broom handle and store it in the garage. Never leave the plastic on the soil over the winter.