Compost Use Guidelines for
Gardens, Landscapes, &
Small Farms
Compost is the product resulting from managed, controlled decomposition of organic
materials. In general, stable, mature compost results from materials reaching a certain
minimum temperature for a specific amount of time with sufficient aeration and
moisture. This process promotes growth of certain microorganisms, converts organic
carbon to carbon dioxide, reduces the viability of pathogens and weed seeds, and
incorporates nutrients into a rich organic matrix.
As an amendment to soil or soilless substrates, compost can beneficially alter chemical,
physical and biological properties. Chemical changes include addition of essential plant
nutrients, increased cation exchange capacity (CEC), and possible liming effects.
Physical changes may include improvements in soil structure, porosity, infiltration,
permeability and water-holding capacity. Additionally, compost can increase microbial
diversity.
Although compost is beneficial, it is possible to use too much compost! Therefore, it is
important to determine “safe” compost application rates to prevent harm to plants and to
maintain healthy, productive soil. “Safe” compost application rates depend on the
physical and chemical properties of the compost, frequency of application (i.e., one time
only or several times per year) as well as soil texture, soil pH and soil fertility. All
recommended application rates herein are guidelines based the chemical properties of
the compost and based on the assumption that soil pH is optimal and there are no
concerns with soil copper (Cu) or zinc (Zn) levels.
Compost Applications Rates
Physical properties: Apply no more than a 3-inch thick layer of compost at any given
time when tilled to 6 inches or 50 percent by volume (or equivalent), regardless of
chemical properties or application frequency. Higher application rates may negatively
affect physical properties of the amended substrate (e.g., too much water-holding
capacity, not enough air porosity).
Application frequency. For maintenance (i.e., application on a given bed or garden at
least yearly), limit application to a maximum thickness of 1 inch total per year, or lower
rates as indicated by chemical properties. For garden or bed establishment (one time
application), apply compost at rates according to chemical properties discussed below.
Chemical properties : NCDA&CS standard waste analysis provides measurements of
the following parameters: soluble salts (SS), pH, sodium (Na), carbon-to-nitrogen (C:N)
ratio, and the essential plant nutrients nitrogen (N), phosphorus (P), potassium (K),
calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), manganese (Mn), Zn, Cu, and
