Basics

  • -“Composting” means the controlled decomposition (decay) of organic material such as yard trimmings, kitchen scraps, wood shavings, cardboard, and paper.
  • -“Compost” is the humus-rich material that results from composting.

Compost Benefits

Plant Nutrition

  • -Compost contains all the essential plant nutrients, including micronutrients such as iron and manganese that are often absent in synthetic fertilizers.
  • -Compost releases its nutrients slowly, over several months or years.
  • -Compost balances both acid and alkaline soils, bringing pH levels into the optimum range for nutrient availability.
  • -Soil enriched with compost retains fertilizers better than lifeless soil does, reducing runoff and water pollution.
  • -Compost can reduce or eliminate your use of synthetic fertilizers.

Beneficial Soil Life

  • -Compost promotes the growth of beneficial microorganisms, insects, and worms, which support vigorous plant growth.
  • -Compost bacteria break down mulch and plant debris (and even nitrogen from the air) into plant-available nutrients.
  • -Compost reduces the need for chemical pesticides because it contains beneficial microorganisms that protect your plants from diseases and pests.

Soil Structure

  • -Compost helps bind clusters of soil particles (aggregates). Soil rich in aggregates is full of tiny air channels and pores that hold air, moisture, and nutrients like a sponge, allowing you to water and fertilize less.
  • -Compost helps sandy soil retain water and nutrients that would normally wash right through.
  • -Compost breaks up tightly bound particles in clay soils, allowing roots to spread, water to drain, and air to penetrate.
  • -Beneficial insects, worms, and other organisms are plentiful in compost-enriched soil; they burrow through the soil keeping it loose and well aerated.
  • -Compost makes any soil easier to work and cultivate.

And…

Compost makes good mulch. It can also be mixed into garden and potting soils.

Buyer's Guide to Compost Quality

Chemical fertilizers that carry a label by law must declare their nitrogen, phosphorus, and potassium (N-P-K) content. Compost contains much less concentrated amounts of these elements, but is typically called a "soil amendment" rather than a fertilizer. Compost is a living organic product that has the unique ability to improve not only the chemical balance, but also the texture and biological characteristics of soils.

Some large-scale compost buyers like the Texas Department of Transportation (TxDOT) have developed detailed specifications for General Use Compost, Erosion Control Compost, and Compost Manufactured Topsoil (soil blend) based on extensive laboratory testing. However, commercial compost sales are not subject to any legal rules for reporting product contents.

Here are a few simple guidelines that can help you make good choices when buying compost products:

  • -Mature compost should be dark brown in color.
  • -It should have a loose, crumbly texture, and briefly hold its shape (but not drip water) when squeezed in your hand.
  • -It should have an "earthy" smell, not an ammonia or "rotten egg," odor.
  • -Rough-textured compost containing un-composted woody chips or shreds can be used as a topdressing mulch around plants, or for erosion control on slopes, but should not be mixed into the soil, as it can reduce the availability of nitrogen to plant roots.

Using Compost in Your Yard

There are a wide variety of applications for compost on your lawn, garden, trees, and planting beds. The amount of compost you need for a particular use will depend on the quality and condition of the soil, the type(s) of plants to be nourished, and the quality of the compost. Ask your prospective compost supplier for references or test results on their product.

The following application rates are “ballpark” only. For more specialized advice, contact the horticulture specialist at your local AgriLife Extension office, city compost specialist, compost supplier, or landscaper. The good news is, it’s very hard to go wrong with good compost.

Typical Compost Application Rates

Application

Approximate Rate

Notes

New grass establishment

1 - 2 inches

Till in to a depth of 4 – 6 inches, depending on soil texture.

Lawn maintenance

1/8 – ½ inch

Aerate compacted soil before applying.
Apply mid-April and/or mid-October according to need.

Planting bed preparation

1 - 2 inches

Till in to a depth of 4 – 6 inches.

Planting trees

Mix 1/3 compost into backfill soil.

Rough up edges of planting hole before backfilling.

Mulching around trees and shrubs

1 – 3 inches

Apply out to drip line. Leave bark and root crowns of trees exposed.

To determine how much compost you will need for a particular application, enter the square footage of the application area and the application rate in the appropriate spaces in this online calculator:

University of Minnesota – Compost Application Calculator

Additional Resources

San Antonio Water System – Compost Application Rates