PlantLife Online

Mulching is the practice of covering the soil surface with a variety of materials for protection and improvement of the soil. Mulching is a pattern we see in nature with fallen leaves, needles, twigs, bark, fallen fruit, and other organic materials. Many benefits are achieved by correctly replicating this pattern in the landscape.

Mulching benefits the soil in many ways which directly improves root systems. Mulching improves soil moisture by preventing water loss from the soil by evaporation. Mulching also prevents crusting of the soil surface which improves water absorption and movement. Mulching provides soil insulation, keeping soil cooler in the summer and warmer in the winter. Organic mulches can improve the soil as the decaying material adds nutrients. Mulch prevents soil compaction. All of these benefits contribute to healthier root systems.

Additional benefits include: reduced soil erosion, a reduction of weeds by preventing germination and inhibiting existing weeds from obtaining adequate resources, and a reduction of soil-borne diseases by preventing splashing, Mulch protects trees and shrubs from damage caused by lawn mowers and other landscape equipment. Mulch adds aesthetic value by adding texture, order, and color.
Mulching can be especially important for new plantings as it aids to maintain soil moisture during establishment. Mulching is also very important for trees. Ideally, mulch should extend 6 to 12 inches beyond the drip line of the tree, encompassing most of the trees roots. This prevents competition of trees with turf and weeds for nutrients and water. Mulching is not just for new plantings and trees, but for entire beds of shrubs, annuals, herbaceous perennials and ground covers.
Mulch should always be applied 2-3 inches from the stem of all woody plants to prevent decay caused by moisture, and should not be more than 2 to 3 inches deep. Excessive amounts of mulch can suffocate plant roots. In anaerobic conditions microbes, primarily bacterium, produce substances toxic to plants such as ammonia gas, methanol, sulfide gas and acetic acid. These potential problems can be mitigated by turning mulch once or twice a month, and by not applying mulch too deep.
Mulches are divided into two categories: organic and inorganic. Organic mulches come from natural materials that will decompose over time, and can attract insects, slugs, and cutworms. Organic mulches include bark, wood chips, leaves, pine needles, or grass clippings. Inorganic mulches do not decompose and do not attract pests. Inorganic mulches include substances such as gravel, pebbles, black plastic and landscape fabrics. The need to replenish mulch depends on the material.

Organic mulch materials
- Wood Chips- typically composed of various sizes and types of wood. If pieces are particularly small additional nitrogen may be required, as decomposition rapidly uses soil nitrogen.
- Pine Bark can be purchased in various size particles ranging from shredded to large nuggets. Pine bark is good for weed control.
- Pine Needles (pine straw) - are good for mulching acid-loving trees and shrubs. Pine needles can be good for mulching sloped areas because they tend to stay in place better than other materials because the needles tend to interlock. Pine needles allow for good air, nutrient, and water penetration.
- Shredded hardwood mulch- decomposes very slowly, is aesthetically pleasing, and good at suppressing weeds.
- Grass clippings- decompose quickly and therefore are relatively temporary. It is best to use dry grass as opposed to fresh clippings. Do not use grass clippings if they are full of weed seed, or if the grass has been treated with herbicides.
- Straw- another quickly decomposing, rather temporary mulch. It is best used in a vegetable garden or newly sown lawn.
- Leaves- most effective when leaves are shredded as whole leaves are easily blown away. As leaves decompose they should be incorporated into the soil and a new layer added on top. Additional benefit comes from oak and beech leaves for acid-loving plants; these leaves lower soil pH as they break down.
Inorganic Mulch Materials:
- Gravel, pebble, and crushed stone- these materials are permanent and can be used in thinner layers. A 1- inch layer of small rocks will provide good weed control. A few cautions for when using rocks: rocks may raise pH by adding alkaline elements and minerals to the soil, rocks may create a very hot landscape environment during the summer months.
- Landscape cloth and woven ground cloth are available in various lengths and widths. They are made of material such as paper or plastic that is treated to resist decomposition. The woven materials allow water and air to move through them better than plastic films. They are very effective in controlling most weeds, but need to be fasted to resist being pushed up by perennial weeds. Like black polyethylene film, better results occur when using organic mulch on top.
Black polyethylene film is an alternative to traditional mulches. It is effective in minimizing soil evaporation and weed growth. In poorly drained areas, it may not allow sufficient drainage and could lead to root disease. Holes can be cut in the plastic to allow water to pass through, and it is available with holes precut. Covering the black plastic with a layer of organic mulch will reduce heat absorption and mask the artificial appearance. Clear plastic is not recommended because it allows light to penetrate the film raising soil temperature and fostering weed growth.
As we imitate the pattern of mulching as observed in nature, many significant and long-lasting benefits are realized. This simple garden practice is one that does not take a large investment of time or resources, but will have powerful effects.