Composting Basics

Composting is the controlled biological decomposition of organic material in an aerobic environment (with oxygen) that generates enough heat to reduce the number of possible pathogens in the initial feedstocks. The are several different methods of composting (windrows, turned windrows, aerated static piles, in-vessel systems, backyard bins, and more). 

Learn more about composting through the frequently asked questions below.

For questions, please contact a staff member.

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Compost is the product resulting from the controlled biological decomposition of organic material that has been sanitized through the generation of heat and stabilized to the point that it is beneficial to plant growth. Compost bears little physical resemblance to the raw material from which it originated. Compost is an organic matter source that has the unique ability to improve the chemical, physical and biological characteristics of soils or growing media. It contains plant nutrients but is typically not characterized as a fertilizer.

Composting helps keep organic matter out of landfills (which reduces greenhouse gas emissions), saves money by reducing the need for fertilizer, water and garden supplies, and helps to limit pollutants contributed to the environment. Composting organic wastes at home or through a commercial composting facility (leaves, yard trimmings, food scraps, etc.) can reduce the waste annually disposed in landfills by 20%.

  • Carbon to nitrogen ratio of the compostable materials
  • Amount of surface area exposed
  • Amount of aeration in the pile
  • Moisture content
  • Temperature
  • Time

  • Physical benefits: it can help improve soil structure and moisture management, thus preventing compaction, increasing water retention, and reducing runoff and erosion.
  • Chemical Benefits: it can help modify and stabilize pH, increase cation exchange capacity, provide macro and micronutrients needed for plant growth, bind contaminants to prevent water pollution, and bioremediate contaminated soils.
  • Biological Benefits: it can help provide beneficial soil biota, suppress plant diseases, and control weeds.

Be aware that the use of incompletely decomposed compost in the garden may damage plants. If unfinished material is used, than the decomposer bacteria in the compost compete with plants for nitrogen in the soil to break down materials. As a result, plant leaves may turn yellow and growth can be stunted. In addition, organic acids in decomposing materials may cause harm to plant roots.

Finished compost qualities:

  • Smells earthy
  • Will not reheat when turned or wetted
  • Looks like dark soil, original trimmings are not identifiable

Immature Compost Qualities:

  • Smells sour or like ammonia
  • Significant heat is generated when compost is turned or dry compost is wetted
  • Is light colored; leaves, clumps of grass or other trimmings are identifiable

  • Soil Incorporant:

    • Stormwater BMPs
    • Erosion and Sedimentation Control
    • Turf establishment
    • Garden bed preparation
    • Crop production
    • Reclamation/remediation
    • Nursery production
    • Sod production
    • Roadside vegetation
  • Growing Media Component:

    • Container/potting
    • Landscape (e.g. rooftop, raised planters)
    • Backfill mixes (tree and shrub planting)
    • Golf courses (e.g. tee, green, divot mixes)
    • Manufactured topsoil
    • Bioremediation
  • Surface Applied:

    • Garden bed mulch
    • Crop production mulch
    • Nursery production mulch
    • Erosion control media
    • Silt/sediment control berm
    • Turf top dressing

  • Bioremediation and pollution prevention
  • Disease control for plants and animals
  • Erosion control
  • Composting of contaminated soils
  • Reforestation and wetlands restoration
  • Habitat revitalization

On flower and vegetable beds:

  • Remove weeds and grass that may grow through mulch.
  • Screen or pick through compost to remove large, woody materials. They may be unattractive and will compete for nitrogen if mixed into the soil.
  • Apply 1"-3" of compost over the entire bed, or place in rings around each plant extending to its outermost leaves.
  • Always keep mulches a few inches away from the base of the plant to prevent damage by pests and disease.

On lawns:

  • Use screened commercial compost, or sift homemade compost through a ½" or finer mesh.
  • Spread compost in ¼" or ½" layers after thatching, coring, or reseeding.

On trees and shrubs:

  • Remove sod from around trees and shrubs as far as branches spread. If this is impractical, remove sod from within a minimum 4" diameter circle around plants.
  • Use coarse compost or material left after sifting. Remove only the largest branches and rocks.
  • Spread 1"–3" of compost.

For erosion control:

  • Spread coarse compost, or materials left after sifting, in layers 2"-4" deep over entire planting area or in rings extending to the drip line.
  • Mulch exposed slopes or erosion-prone areas with 2"-4" of coarse compost.

Grasscycling - the natural decomposition of grass clippings left on the lawn after mowing - encourages those tending lawns to leave clippings where they are cut instead of bagging them. Grass clippings are a major component of residential yard waste, sometimes as much as 50 percent. Four good reasons to start grasscycling:

  1. You'll need less fertilizer.
  2. You'll save water.
  3. You'll save your community money.
  4. You'll also save one of your most precious resources: time.

Xeriscaping is landscaping with less water while maintaining a traditional look. Americans routinely overwater their lawns by as much as 20 to 40 percent. By not overwatering, water use can be reduced by about 12 percent during summer months.

Wormcomposting, vermicompost, or vermiculture is a process that uses earthworms to break down organic material.  Several earthworm species can consume organic wastes rapidly and then fragment the materials into fine particles. These particles contain essential nutrients such as nitrogen, phosphorus, potassium and calcium that are valuable to plant growth.  Vermicomposting (the process) generates vermicompost or wormcompost (the product) which tends to be higher in nutrients than regular compost. To learn more about this, please visit NCSU's Vermiculture page.