One of the best cultural practices in the landscape is the application of mulch around plant material. Mulch has numerous benefits: It enhances the appearance of the landscape and reduces the evaporation of water from the soil, which prevents fluctuations in soil moisture levels.
It also prevents "crusting" of the soil surface, the formation of a hard layer that is difficult for water to penetrate, where as the presence of mulch improves the ability of water to infiltrate the soil. Using mulch is part of "xeriscaping," which is the development of a low water use landscape.
Mulches help keep the soil temperatures stable and insulate the roots from temperature extremes. Covering the bare soil reduces the germination of weeds that compete with the desired plants for moisture and nutrients. Mulch also acts as a barrier between the plants and the soil reducing the likelihood of soil borne plant diseases, it adds organic matter to the soil and reduces soil erosion.
Fine texture organic mulches, such as pine bark, pine straw, pine bark mini-nuggets and shredded hardwood mulch are the most effective and beneficial for the landscape than the coarse textured mulches like large pine bark nuggets. The fine textured mulches are better at holding moisture in the soil, do not form impenetrable mats and permit the infiltration of water, oxygen and fertilizer into the soil.
Fall leaves are excellent mulch for use due to their abundance. They do not cost anything; however, leaves do not have the uniformity or neatness like the fine textured mulches. Do not use inorganic mulches such as lava rock, marble or gravel since these materials absorb the intense heat from the sun which can damage the plants.
Apply at least 3 to 4 inches of fresh pine straw around your shrubs and roughly 3 inches of pine bark or shredded hardwood mulch. Around trees and shrubs, always pull back some of the mulch 2 to 3 inches away from the main trunk.
Too much mulch increases the risk of causing the roots to grow mostly in the shallow, upper layers due to decreased ability to absorb oxygen and water, and it can increase the risks of root diseases. Sometimes excessive mulch is applied to tree wells, which is often referred to as "volcano" mulching, and this can cause rotting of the roots and the main trunk.
Landscape fabrics are beneficial in that they allow for the penetration of water and air. However, they are difficult to install will not prevent the germination of certain weeds like nutsedge and must be covered with an organic mulch. The same is true with using recycled newspapers. Plastic film should never be used since water and air can not penetrate it.
Removing the old mulch every year and replacing it with new mulch is not necessary since the organic mulch rots down due to the activity of the microbes. Fresh mulch can be applied directly to the top of the already-existing, partially rotted mulch until it is 3 to 4 inches high. For example, if the existing a layer of mulch is 2 inches thick, then add only a thin layer of mulch, roughly one inch.
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. If you have any questions concerning mulching, call the Gwinnett County Extension office.
Timothy Daly is an agricultural and natural resource agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010 or firstname.lastname@example.org