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Harry A. J. Hoitink, The Ohio State University, Ohio Agricultural Research and Development Center, Plant Pathology; Daniel A. Herms, Pierluigi Bonello, |
Timing of Application
In Ohio's climate, composts that are high in salinity (composted manures, sludges) and fresh materials that have not been composted should be applied in the fall or winter when pathogens and the crop are least active. This allows time for leaching of salts and for decomposition and establishment of beneficial effects. Composted sewage sludges and manures that are high in salinity often increase disease pressures rather than provide control, if applied in the spring or summer when Phytophthora and Pythium are most active.
The best approach is to blend materials high in nitrogen content and salinity with woody mulches to provide long-lasting beneficial effects. After two to four months of composting, these blends can be applied as mulches at any time of the year and provide beneficial effects consistently.
Optimum Depth of Mulch Layer
Most mulches need to be applied to a depth of two to three inches to provide weed control. Some landscapers apply mulches to a depth of four to six inches, or even deeper. This can decrease colonization of trees by mycorrhizal fungi and increase root diseases such as Armillaria trunk decay and root rot. In contrast, mycorrhizal fungi are stimulated by organic amendments if the correct amount and type of material is applied, thus promoting plant health and vigor.