Tuesday, May 8, 2012


 Mulch is simply a layer of material that is laid over the surface of the soil.  It may be classified as organic such as ground bark, straw, grass clippings, manure and compost, or inorganic (synthetic) like plastic sheeting, paper and rocks.   
Using mulch in the garden has many benefits. 

  •         Weed Control
One of the most important benefits is weed control.  Putting down a layer of mulch will prevent light from reaching the soil. Many weed seeds will not germinate, or if they do, there will not be enough sunlight for photosynthesis to occur.  When using materials like compost and wood chips, at least 3 inches of material is required for good weed control, and preferably 4 – 6 inches. Note: some vines and grasses, which have a well-established root system, will be able to grow through the layer of mulch to the surface. In addition, in areas of high rainfall, airborne seeds landing on the mulch will be able to germinate and grow when there is adequate moisture.  

  •      Water conservation
Water conservation is another benefit to mulching.  The mulch will actually reduce water evaporation from the soil.  Even in areas of high rainfall, the mulched plants will have a better chance of surviving during periods of drought.   In addition, mulches will also reduce runoff and erosion and increase the permeability of the soil surface.
Mulching may not be a good idea in heavy clay soils since they already hold soil moisture. Extending the period of moisture retention in a clay soil could lead to crown and root diseases. 

  •         Soil Fertility
Many of the common mulches like compost and wood products do not contain large amounts of nutrients, and therefore an occasional, small application of these products will not supply the plants with adequate nutrition.  However, applying mulch at a 6 – 12 inch thickness on a consistent basis, eventually will release macro and micro nutrients into the soil.  This may not replace any fertilization program but over time will substantially add to the fertility of the soil.  Mulches that have a high carbon to nitrogen ratio such as wood, sawdust and straw, may cause a short term, initial nitrogen depletion at or near the soil surface.  Simply apply a small amount of a high nitrogen fertilizer when using large amounts of wood/sawdust/straw mulch to flower beds and around other shallow rooted plants.

  •      Biological control
Large amounts of mulch (up to 24 inches) applied to the soil surface have the potential of controlling root rot diseases.  As the mulches breakdown, they create soil conditions which are deleterious to pathogenic soil organisms such as nematodes and root decaying fungi.  This has been especially true in the control of avocado root rot (Phytophthora cinnamomi).

As an alternative weed control, shredded paper can be used along pathways in the garden. Once wet, it will form a thick mat which most weeds will not penetrate.