The nitrogen-depleting effect of mulch diminishes over time as it decomposes. As
microbes die, the nitrogen they contain is released for use by plants unless the carbon source is
replenished by adding fresh mulch. Nitrogen immobilization by microbes will probably have a
greater impact on herbaceous plants and newly transplanted woody plants than on wellestablished
trees and shrubs with extensive root systems. Nevertheless, it may be best to reserve
mulches with a high C:N ratio for use away from plants, such as on paths. Alternatively, these
products can be blended with composted materials with a low C:N ratio, such as yard waste,
animal manure or sewage sludge.