Nature mulches plants with fallen leaves and other organic materials. Mulching, as practiced by gardeners, is merely an adaptation of this natural process.
Advantages of Mulching
Adding a layer of mulch around trees, shrubs, and planted beds offers several advantages. Mulch conserves soil moisture. Evaporation of water is greatly reduced when the soil is protected from the direct rays of the sun and moving air. Mulch prevents rain from compacting the soil surface as well as decreasing soil erosion.
Another important advantage of a mulch is the control of weeds. Mulch greatly reduces germination of weed seeds and can smother existing weeds. Mulch can be used with a preemergence herbicide, which kills weeds before germination, as an additional weed control strategy. It is especially important to mulch rather than cultivate around shallow-rooted plants, such as rhododendrons, azaleas, and camellias.
Controlling soil temperature is another plus with mulch. Lower and more uniform soil temperatures in summer favor root growth and beneficial bacterial activity in the soil. High summer temperatures may injure roots and soil microorganisms near the surface of the soil. In winter, mulch insulates the root zone and protects roots from frost penetration and buffers against freeze-thaw cycles. Mulch maintains moisture in the soil, which is especially important for evergreen plants that continue to absorb moisture during the winter months.
Organic matter used as a mulch can improve soil structure, drainage, and aeration. As it decays, the organic mulch material becomes incorporated into the topsoil. Decaying mulch adds nutrients to the soil.
Mulching material, such as pine bark or pine needles, improves the appearance of the garden. It is valuable for covering beds near the house or in areas where neatness is important. Mulch can replace grass or groundcovers in areas that are difficult to mow or maintain. Mulching around trees and shrubs can prevent damage to plants from mowers and trimmers.
Disadvantages of Mulching
Mulching has a few disadvantages. First, the cost of some materials can be a drawback to large-scale mulching. Some mulches are also not readily available. If large quantities are required, buying bulk loads of mulch is less expensive than buying mulch by the bag.
Sawdust and wood chip mulch have a high carbon content and can remove nitrogen from the soil. This is easily corrected by using additional nitrogen fertilizer.
Heavy mulching over a period of years results in a mat of mulch and soil covering the crown area of the plants. Plant roots can also develop in excessive mulch layers. Rake old mulch to break apart matted layers before applying a new mulch layer.
Avoid piling excessive mulch at the trunk of trees. This volcano mulching causes rot by holding moisture against the trunk.
Materials for Mulching
Apply 1 to 2 inches. May contain weed seeds. Should be well composted to prevent burning plants and minimize weeds sprouting.
Apply 1 to 2 inches. Sawdust is low in plant nutrients and decomposes slowly. Sawdust tends to pack down and prevent water penetration. Additional nitrogen fertilizer is recommended when using sawdust.
Apply 2 to 3 inches. Well-rotted materials preferred. Wood chips decompose slowly. Chips can be used fresh if additional nitrogen fertilizer is added to the soil at a rate of 1 pound of fertilizer per 100 square feet. Keep away from building foundations as wood chips can encourage termites.
Apply 2 to 3 inches. Bark is ground and packaged commercially and can be found in various sizes. Pine bark is an attractive, dark-colored mulch in
Apply 2 to 3 inches. Ground corncobs are excellent for improving soil structure.
Apply 3 to 6 inches. Pine needles will not mat down, are fairly durable, and allow good penetration of water and air into the soil. Great for winter protection on perennials because of its nonmatting quality.
Apply 2 to 3 inches. Compost will slowly release nutrients into the soil for plant uptake.
Whole Tree Leaves
Apply 3 to 6 inches. Leaves are an excellent source of humus. They rot rapidly and are relatively high in nutrients. Not recommended for herbaceous perennials.
Shredded Tree Leaves
Apply 2 to 3 inches. Shredded oak leaves as a mulch are especially valuable around acid-loving plants, such as azaleas, camellias, and rhododendrons. Shredded tree leaves are less prone to matting than whole leaves.
Apply 3 to 6 inches. Hay is often considered unattractive and may contain weed seeds, but it is readily available.
Apply 1 to 2 inches. Grass clippings tend to mat and can repel water if they dry out. Should not be applied deeper than 2 inches. This material is high in nitrogen. Mixing grass clippings with other mulch materials will add nitrogen while preventing matting. Do not use grass clippings from a lawn that has been treated with a weed killer.
Apply 6 inches. Hay straw is unattractive but readily available. Hay straw is lower in nutrients but can supply considerable potassium.
Apply 1 to 2 inches. Pecan hulls as a mulch are safe for landscape plants and durable, but their availability is limited. Pecan hulls will stain concrete and are prickly if walked on.
Apply 1 to 2 inches. Limited use but particularly good for rock garden plantings.
Apply 1 to 2 inches. Stone chips are extremely durable; holds down weeds but does not supply plant nutrients or humus.
Newspaper and Cardboard
Apply 1⁄2 to 1 inch. Should be covered with another mulch to improve appearance and prevent scattering.
Landscape weed fabrics will allow water and air to penetrate into the soil. Will prevent most weeds, but grasses may grow through the fabric. Can be covered with another mulch to improve appearance.