When purchasing compost to be used for turf establishment or incorporation into soil as a postconstruction soil amendment, look for these specifications.
Link to this table

Parameter Parameter Definition Range (Provided by G. Black, MPCA, 2007)
Source Material/Nutrient Content Compost typically comes from biosolids/animal manure or yard wastes. Compost made from biosolids and animal manure typically contains more nutrients.1
  • N: 0.5 – 3 (mg/kg)
  • P: 0.5 - 1.5 (mg/kg)
  • K: 0.5 - 1 (mg/kg)
  • NPK ratio: 2:2:1 - 4:4:2
  • C:N ratio: 6:1 - 20:1
Maturity Maturity refers to the level of completeness of the composting process. Composts that have not progressed far enough along the decomposition process may contain phytotoxic compounds that inhibit plant growth.2 Seed emergence and seed vigor = minimum 80% relative to positive control
Stability Compost stability refers to the biological activity in the composted material. Unstable composts may use available nitrogen in the soil and stunt plant growth. CO2 Evolution rate: < 8 mg CO2-C/g-OM/day
pH pH is a measure of acidity/alkalinity. Amending soil with compost can alter soil pH, which in turn can improve plant growth. 5.5 – 8.5
Soluble salts The term “soluble salts” refers to the amount of soluble ions in a solution of compost and water. Because most plant nutrients are supplied in soluble form, excess non-nutrient soluble salts can inhibit plant growth. Varies widely according to source materials for compost, but should be < 10 dS/m (mmhos/cm)
Organic matter Organic matter is a measure of the amount of carbon-based materials in compost. There is no ideal range of organic matter for compost, but knowing the amount of organic matter in compost may help determine application rates for specific applications. 30-65% dry weight basis
Particle size It is helpful to know the size of particles in a compost product. There is no ideal range, but particle size does influence the usability of a compost product for a specific application. Pass through 1-inch screen or less; 3/4 inch is preferable per MnDOR Specification 3890
Biological contaminants (weed seeds and pathogens) Biological contaminants consist of pathogens (disease causing organisms) and weed seeds. High temperatures will inactivate both types of biological contaminants. Minnesota State composting rules require commercial composting operations to hold temperatures over 55 degrees C over an extended period of time to destroy pathogens. In addition, compost operations must monitor the process to prove that these conditions have been met. Meet or exceed US EPA Class A standards, 40 CFR §503.32(a) levels
Physical contaminants (inerts)* Inerts are man-made materials (like pieces of plastic or glass) that do not decompose. There is no ideal range but they may be aesthetically unpleasing and add no value to the compost. < 1% dry weight basis3
Trace metals Trace metals are elements that can be toxic to humans, animals, or plants at elevated concentrations Meet or exceed US EPA Class A standards, 40 CFR §503.32(a) levels
* Inert material should not be present in adequately screened, vegetated waste compost. Caution should be used when the compost originates as mixed municipal or unscreened compost.

1 MnDOT Grade 1 compost is derived from animal material; Grade 2 compost is derived from leaves and yard wastes. See MnDOT Specification 3890
2MnDOT Specification 3890 states: "Considered mature and useable when 60 percent decomposition has been achieved as determined by an ignition-loss analysis test method and any one additional test method including the Solvita test value of equal to or greater than 5. This means that the compost product has no offensive smell, no identifiable organic materials, and will not reheat to more than 20 °F [11 °C] above the ambient temperature."
3 MnDOT Specification 3890 states: "< 3% at 0.15 in [4 mm]"

This page was last edited on 2 August 2022, at 14:19.