Application of these products in the late fall or mid-winter allows for leaching of salts and provides positive rather than negative effects. Several producers of composts have learned to monitor and control the salinity and fertility effects of composts. It is possible today, therefore, to use these products beneficially at any time of the year and avoid negative side effects. The best approach is to blend high nutrient content materials with tree bark to provide long-lasting beneficial effects. Most mulches need to be applied at a two-inch depth to provide weed control.
Some landscapers apply mulches to a depth of four to six inches.
Wood chips applied to a depth of four inches decrease the colonization of trees by mycorrhizal fungi as shown in a reforestation trial in Alberta. Many reports have shown that mycorrhizal fungi are stimulated by organic amendments if the correct amount of material is applied, and this also promotes plant health and vigor. Some mulches, as mentioned earlier, can be very high in nutrient content and salinity. The nutrients in these materials must be considered or toxicity may result. Fertility guidelines must be followed for these materials.