Ideally, it must allow water and air to enter and exit the soil. Mulch also can insulate a plant and its roots from the effects of extreme temperature fluctuations. Mulch should be attractive, relatively odor free and should stay in place.
Mulch can benefit soils by:
- reducing the amount of water lost from evaporation.
- protecting trees and other landscape plants from mechanical injury due to mowers and string trimmers.
- protecting exposed roots from lawn mowers.
- reducing soil compaction caused by people and equipment by diverting traffic around landscape beds.
- reducing soil and wind erosion, especially on steep slopes.
- reducing incidence of disease by protecting above-ground plant parts from splashes that carry soil-borne inoculum.
- reducing fruit rot by eliminating contact between fruit and soil.
- reducing winter injury by minimizing temperature variation.
- helping control weeds.
- maintaining cooler soil temperatures during the summer.
The depth of mulch depends on the type of soil, plants and mulch used. Layers thinner than recommended depths may need to be replenished more often and may not give the desired benefits. Thicker layers may reduce the amount of oxygen in the soil and encourage plants to root in the mulch layer rather than in the soil. Thick layers may also shed water and prevent it from moving into the soil.
During wet periods, avoid thick layers of mulch around plants in heavy soils such as clays and clay loams. Thick layers may reduce soil oxygen and injure plants. When conditions are cool and wet, mulch should be pulled away from plants to ensure good air and water exchange.
Never apply mulches against the bark of woody trees or shrubs. This may encourage insect and disease problems to occur on thin-barked and wounded trees. It also may provide protected chewing access for small rodents and other animals, which can severely injure the bark and cambium.
Organic mulches usually are replenished in the spring. A quick raking of the existing mulch will help determine how much mulch should be added. Raking also will break up water-shedding layers.
Some plants, such as cool-season vegetables, will benefit from early mulch and will produce later into the season if kept cooler. However, most plants benefit from waiting to apply new mulch until soil temperatures have warmed up. Prior to mulching, beds should be well watered if needed.
Late-season organic mulches are applied after at least two hard freezes. Applying mulch earlier will insulate the soil and keep plants from hardening off. Late-season mulching is especially important for recently installed plants to prevent frost heaving, the freezing and thawing action of the soil that may push plants out of the ground.
Herbicides can be used in conjunction with mulches to improve weed control. Some herbicides may stain mulches and hardscape features, so use caution when using herbicides in landscape beds where annuals or new plants are being established. Some herbicides may stunt root development if applied before transplants become established.
Mulches are an important component of the landscape. When applied appropriately, they serve many positive functions.
Source: Roch Gaussoin, University of Nebraska–Lincoln
