GARDENING IN GWINNETT: Using mulch helps prevent weeds, plant diseases

The application of mulch is an important cultural practice in the home landscape.

The use of mulch helps the soil to retain moisture, improves the appearance of the landscape and has numerous other benefits. Using mulch is an important component of "xeriscaping," which is the implementation of several tactics that reduce the need for the application of water in the landscape.

Mulch reduces the evaporation of soil moisture, thus making more of it available to plants. It also prevents the formation of crusty soil, which improves the infiltration and movement of water in the soil. Mulch insulates the soil and helps prevent drastic fluctuations in soil temperature, thus keeping the roots cooler in summer and warmer in winter. It also adds organic matter to the soil and reduces soil erosion.

Covering the bare soil with mulch reduces the germination of weeds that compete with the desired plants for moisture and nutrients. It also acts as a barrier between the plants and the soil reducing the likelihood of soil borne plant diseases. Mulched areas also act as a buffer zone between the turfgrass areas and ornamentals which prevents damage to them from lawn mowers and other landscaping equipment.

Fine texture organic mulches, such as pine straw, pine bark mini-nuggets and shredded hardwood mulch, are preferable to the coarse textured mulches like large pine bark nuggets. The fine textured mulches do a better job of holding moisture in the soil. Avoid using lava rock, marble, or gravel as mulch. These materials absorb the intense heat from the sun, which can be harmful to the plants.

Apply at least three to four inches of fresh pine straw around your shrubs or roughly three inches of pine bark or shredded hardwood mulch. Around trees and shrubs, always pull back some of the mulch two to three inches away from the main trunk. Excessive mulch may cause the roots to grow mostly in the shallow upper layers of the soil due to decreased ability to absorb oxygen and water, as well as increase the risks of root diseases.

Plastic film should never be used as a mulching material. It can hold in too much water leading to root rot. Landscape fabrics are preferred since they are porous and allow for the penetration of water and air. However, they are difficult to install, they will not prevent the germination of certain weeds like nutsedge, and they must be covered with organic mulch.

Removing the old mulch every year and replacing it with new mulch is not necessary since the organic mulch rots due to the activity of the microbes in the soil. Fresh mulch can be applied directly to the top of the already-existing, partially rotted mulch until it is three to four inches high. For example, if the existing a layer of mulch is two inches thick, then add only a thin layer of mulch, roughly one inch.

In conclusion, applying the proper mulch to the home landscape creates a more pleasing appearance and also helps promote good plant health in a variety of ways.

Timothy Daly is an Agricultural and Natural Resource Extension Agent with Gwinnett County. He can be contacted at 678-377-4010 or tdaly@uga.edu.