Applying a 2 to 4 inch layer of organic mulch can mimic a natural forest environment where tree roots are provided rich, oxygenated, soil containing nutrients and beneficial microorganisms. The forest floor is basically nature’s way of composting; replenishing and recycling nutrients without human intervention. Good soils make for good roots, resulting in healthy trees.
Organic mulches include wood chips, pine needles, hard and softwood bark, cocoa hulls, leaves, compost mixes and a variety of other plant products. Decomposition rates are dependent on the product used. Those that decompose faster must be replenished more often to maintain looks and benefits.
Additions to mulch should be made to maintain proper depth. Fluffing the older layer of mulch, before adding more, can prevent the formation of a hard surface that may deflect water rather than retain it.
Inorganic mulches are also available and include stone, lava rock, pulverized rubber, geotextile fabrics and others. Unlike the organic mulches, they do not decompose and therefore don’t require frequent replenishment. On the flip side, inorganic mulches do not improve the soil structure or provide desired nutrients that organic mulches do. Perennial groundcovers are often used as a mulch alternative. Some gardeners even utilize colorful annual flowering plants in circular beds around the base of trees as a substitute for mulch.
Proper mulching has a plethora of benefits. It reduces soil moisture loss and provides insulation, protecting roots from extreme temperatures. Mulch aides in weed control by providing a barrier between the seed and the sun.
It can also deter pathogens. Many fungal diseases that affect plants (leaf spots, etc.) will
over-winter or hibernate on fallen plant leaves and/or twigs. As soon as the environment
stabilizes and the pathogen becomes happy, it will pop right back up to re-infect.
Mulch can also reduce the potential for damage from lawn mowers and string trimmers. Bark wounds allow for the entry of insects and disease, both of which have the potential to cause serious damage.
As beneficial as mulch is, too much can be harmful, especially for trees. Although the generally recommended mulching depth is 2 to 4 inches, many landscapes are fallingvictim to the plague of “volcano mulching” or excessive piles of mulch materials applied around the bases of trees.
Excessive mulching keeps moisture in direct contact with the bark, which suffocates the cells that transfer food up and down the plant. When this supply of food is limited, the roots die back. This leads to less water uptake, and the tree goes into general decline, leaf drop, and potentially premature death.
Secondary problems, such as wood boring insects and fungi, move into plants weakened by improper mulching. Voles, also known as field mice, tend to migrate to deep mulch rings and chew at the bark and root system of the tree.
If trees have been over mulched, remove the excess using a shovel or trowel. Be careful not to injure the trunk. Apply new much properly, remembering that more is not always better.