Thursday 29 June 2006


Mulching your landscape can have tremendous benefits. Mulching incorrectly can cause significant problems.

Mulching is the practice of layering two to four inches of shredded, chipped bark or wood chips to cover the root zone of trees and shrubs. Mulching mimics the natural process of leaves and debris falling to the forest floor in the fall. If you walk in the forest in the late fall this leaf mulch layer will be at its maximum depth. Decaying over winter this mulch layer decomposes into nutrients. This thick layer will have been reduced to a thin mushy crust by spring when the plants begin to grow.

The primary benefit of mulch is moisture retention. Maintaining moisture in the soil increases the amount of fine root growth. Increased root area results in improved tree health and drought tolerance. Keep in mind that too much mulch can decrease the amount of air in the soil and suffocate roots. Ideal soils contain equal parts of air, water and physical soil. Mulching can be expensive if you use bagged imported materials. A low cost locally available material may make sense for your landscape. With the increased popularity of industrial wood chippers used by arborists to recycle tree waste, an affordable mulching material is at hand.

Mulch has varied properties based on the parent material. Typically composted hard wood chips are the preferred material for most mulching. Ideally the mulch should sit for a period to break down and age. During this process bacteria partially digest the fresh brightly colored wood chips and turn them a darker shade of brown. This process is more than just cosmetic. If you put freshly chipped material in your landscape the decomposition process may rob your trees and shrubs of essential nutrients, especially nitrogen. In the initial stages of decay microbes take nitrogen from the surrounding soil. As the mulch ages this process reverses and the decaying mulch provides a slow released source of nitrogen and other macro and micro nutrients. Wood chips from pine or spruce will acidify the soil as they decompose. You can use this to your advantage if you have plants that prefer these conditions.

Once you have your supply of aged wood chips, weed the area to be mulched. Put the mulch in an even layer 2 to 4 inches thick. Do not allow the mulch to touch the bark of the trees and shrubs directly. Leave a gap of 3 to 6 inches between the bark of the tree and the mulch layer. Don’t pile the mulch against the tree like a mulch volcano. Try to be consistent with the depth of your mulch.

Mulch should be spread out to the drip line on most small trees. The drip line is an imaginary line drawn from the tip of the longest branch to the ground. When rain falls this is where the drops of water will drip to the ground. While it’s not necessary to completely remove your mulch in the spring it is a good idea to refresh it. Refresh your mulch annually by raking it out and adding new material to maintain the 2 to 4 inch depth. If the mulch is breaking down slowly you may only have to level and adjust the depth with out adding new material. Make sure the mulch is not becoming compacted an excluding air. Mulch is a great benefit to your landscape when applied wisely. We will continue with mulching problems and solutions next time.