Bark mulches are a type of organic mulch, meaning this mulch is a product of plant residue and breaks down over time. It comes in a variety of types, including shredded bark, bark chips and chunk bark. Most commercial bark mulches sold are made up of redwood, spruce logs, Douglas fir and pine, as a byproduct of processing.
Mulching is one of the most important ways to maintain healthy landscape plants. A mulch is any material applied to the soil surface for protection or improvement of the area covered. Mulching is really nature’s idea. Nature produces large quantities of mulch all the time with fallen leaves, needles, twigs, pieces of bark, spent flower blossoms, fallen fruit and other organic material.
Benefits of Mulching – When applied correctly, mulch has the following beneficial effects on plants and soil:
- Mulches prevent loss of water from the soil by evaporation.
- Mulches reduce the growth of weeds, when the mulch material itself is weed-free and applied deeply enough to prevent weed germination or to smother existing weeds.
- Mulches keep the soil cooler in the summer and warmer in the winter, thus maintaining a more even soil temperature.
- Mulches prevent soil splashing, which not only stops erosion but keeps soil-borne diseases from splashing up onto the plants.
- Organic mulches can improve the soil structure. As the mulch decays, the material becomes topsoil. Decaying mulch also adds nutrients to the soil.
- Mulches prevent crusting of the soil surface, thus improving the absorption and movement of water into the soil.
- Mulches prevent the trunks of trees and shrubs from damage by lawn equipment.
- Mulches help prevent soil compaction.
- Mulches can add to the beauty of the landscape by providing a cover of uniform color and interesting texture to the surface.
- Mulched plants have more roots than plants that are not mulched, because mulched plants will produce additional roots in the mulch that surrounds them.
Bark mulches also adds aesthetic appeal and also helps to improve the health of a garden. This type of mulch is long-lasting and less likely to blow away. Bark offers an excellent form of weed control. This type of mulch is readily available and over time, it can help reduce soil compaction. Bark mulch decomposes more slowly than wood chips, so you don’t have to replenish it as frequently.
Now, much like anything, there are a few disadvantages to Bark Mulch. With bark mulch use, you should also use a nitrogen fertilizer if not using aged mulch, as “green” mulch has not had time begin decomposition and can rob soil of nitrogen. Bark mulch applied too deeply around plants can cause plant injury by reducing soil oxygen. Don’t use bark mulch in beds where you grow annuals because you need to turn that soil over each year. Chipped bark mulch can float, so it not ideal for use in areas with heavy rainfall where standing water can accumulate or there may be surface runoff. Sour mulch is problem that occurs when mulch is spread too thickly and the inner layer is deprived of oxygen. If your mulch emits a bad odor, spread it out into a thin layer, spray with water and allow it to air dry for a few days.
Bark Mulch isn’t the end all be all of mulches. This is just one type (organic) of a wide range of mulches that you can use for various purposes. Here are some examples of the different types of materials that classify as mulch.
Organic Mulch Materials
Your yard “trash” can be recycled as mulch with the advantage of retaining the nutrients found in these organic materials, in addition to saving money otherwise spent in transporting and disposing of the yard trash.
- Grass Clippings – The best use for grass clippings is to leave them on the lawn. Grass clippings will decompose rapidly, adding nutrients back into the soil. A two-inch layer of grass clippings provides weed control if they are not full of weed seeds. It is best to build up the layer gradually using dry grass, not fresh clippings, to prevent the formation of a solid mat. Be careful not to use clippings from lawns that have been treated with herbicides.
- Hay and Straw – Never use hay for mulch since it contains too many weed seeds. Straw decomposes rapidly, so you will have to replenish it to keep the weeds down. Straw is not very ornamental and is best for a vegetable garden or over newly sown lawns. Straw will improve the soil as it decays.
- Leaf Mold – Leaf mold has a tendency to form a crust, preventing water from penetrating into the soil. It is better to use leaf mold as a soil amendment than as a mulch.
- Leaves – A 2- to 3- inch layer of leaves provides good weed control. It is best to shred the leaves coarsely, using a shredder or your lawn mower. Whole leaves have a tendency to blow away, while finely shredded leaves do not allow water to penetrate. Oak and beech leaves help to acidify the soil for acid-loving plants. Leaves are usually easy to get, attractive as a mulch, and they will improve the soil once they decompose. After the leaves decompose, dig them into the soil and add a new layer of mulch on top.
- Pine Bark – A 2- to 3- inch layer of pine bark is good for weed control. Pine bark makes an attractive, usually dark-colored mulch. It can be purchased in various particle sizes, from shredded to large-sized particles, called nuggets. Large pine bark nuggets float in water and may not stay in place during a heavy rain. They may also attract termites and other insects.
- Pine Needles – A 2- inch layer of pine needles makes an excellent mulch for acid-loving trees and shrubs. This mulch is very attractive and allows water to penetrate easily.
- Shredded Hardwood Mulch – This mulch is good at suppressing weeds. It does not wash away easily. It decomposes relatively slowly, and it is very attractive.
- Wood Chips – This material contains bark and pieces of wood of various sizes and makes an attractive mulch. A 2- to 3- inch layer of wood chips provides good weed control. Small wood chips decompose very rapidly using nitrogen from the soil, which needs to be replaced by nitrogen fertilizer. Wood chips may attract termites and other insects.
- Pecan Shells – Pecan shells make a long-lasting, attractive, dark brown mulch that is effective in retaining moisture in the soil. Availability is usually limited to areas where pecans are processed.
Inorganic Mulch Materials
- Gravel, Pebbles and Crushed Stone – These materials are permanent and are best used for permanent plantings such as foundation plants. A 1- inch layer of small rocks will provide good weed control. Do not use them around acid-loving plants since the rocks may add alkaline elements and minerals to the soil. These materials reflect solar radiation and can create a very hot landscape environment during the summer months.
- Black Plastic – Black polyethylene film is very effective in preventing weed growth. It also holds water in the soil. Therefore, plastic is not recommended for poorly-drained areas as it may cause the soil to remain too wet, which could result in root disease problems. You may have to cut holes in the plastic if water does not go through it. There is black plastic available that has small holes in it to help with drainage. If exposed to sunlight, black plastic is broken down fast, losing its effectiveness as a mulch. However, if you bury black plastic in the soil, it will last for many years. Covering the black plastic with a layer of wood chips or pine needles will reduce heat absorption and mask its artificial appearance.
- Clear Plastic – Clear plastic will not suppress weed growth because light penetrates the film and raises the soil temperature, which may result in an increased growth of weeds in early spring.
- Landscape Cloth or Woven Ground Cloth – Materials woven of fabric, plastic or paper are available in various lengths and widths. The materials are treated to resist decomposition. Unlike plastic films, woven materials allow water and air to move through them. They are very effective in controlling most weeds, although some grasses may grow up through the holes in the fabric. Landscape cloth needs to be fastened down so it will not be pushed up by perennial weeds. Better moisture, temperature and weed control will be obtained by adding several inches of another mulching material on top of the landscape cloth.
- Aluminum-coated plastic and foil – One layer of either one of these materials provides excellent weed control. These materials decompose very slowly, but they are very expensive and quite unattractive mulches.
- Ground Rubber Tires – Mulches made of ground rubber tires do not decompose and therefore, never need to be replaced. The use of ground rubber tires is relatively new and its effectiveness as a mulch is still being evaluated.