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Washington State University

Home Composting

Why Should We Compost

Compost contains valuable nutrients that could replace or supplement use of commercial fertilizers by homeowners.

Proper home composting of organic garden wastes can reduce air pollution, reduce the volumes at the landfill or incinerator.

Volunteer home composting is the most cost effective method of dealing with the yard and compostable kitchen waste.

Many organic materials which you may have been burning or throwing in the garbage is recyclable by composting. Composting being the most efficient way to divert organic wastes from our county’s solid waste stream.


What Materials may be Composted:

grass clippings




chopped cornstalk


farm manure


hedge clippings


kitchen vegetable & fruit scraps


Do Not Compost:

pig and pet manure

fats & oils

meat scraps

diseased plants

vegetation treated with fungicides

perennial weeds, such as: morning glory, quack grass, other hard to kill weeds



Locate the compost pile or bin in an inconspicuous location. A shaded area is preferred. Place it close to water since the decomposition needs moisture. Don’t locate compost piles under trees, because tree roots will invade a compost pile rapidly in the lower layers.

Size of the Compost Pile

The size of a pile needed may vary greatly with the amount of material available. A good size is 4 by 4 feet and 5 feet high. A minimum of 3 by 3 feet and 4 feet high is necessary to reach the high temperature of 150°. These high temperature is a requirement for the composting process, and is needed for killing weed seeds and disease bacteria. You can add small quantities if you can’t generate two cubic feet of materials at one time; it just takes a little longer to break down into compost. Although it is possible to stack the compost in a loose pile, decomposition is more efficient in a contained bin or enclosure. The sides should be open enough to provide some air movement through them. One side should open for turning and removal of the compost.

Many types of materials can be used for building enclosures. Scrap lumber, woven wire fencing, chicken wire, cement blocks are all possibilities. Some wire fencing is too loose to contain smaller materials. Line the inside with some plastic (containing some aeration holes). Pile bricks or concrete blocks without mortar. Leave space between some of them to allow adequate air movement through the sides.

Starting a Compost Pile

Starting the compost pile is usually described in terms of layers. Layering provides the quickest and most complete decomposition. The pile may be started directly on the ground. However, you need to provide aeration to the bottom of the pile and drainage. Dig a trench across the base of the area and cover with a stiff wire mesh before starting the layers. Begin the pile by spreading a layer of coarse organic material over the area.

First pile a layer of 6-8″ of organic materials, then add a layer of 1-2″ nitrogen rich material, such as farm manure, (no pig manure) or 10-6-4 fertilizer. Then add good soil or old humus. Repeat the process until the bin is full. You don’t need special compost activators or starters when soil, old compost or fertilizers are used.

Shredding or Grinding

Shredded or chopped materials decompose the fastest. If a shredder is available, then shred coarse organic matter. Some materials such as leaves and grass clippings tend to mat. Place these in layers only 2″ to 3″ thick. Better to shred or chop this materials in small pieces.

Moisten, but do not soak the layer of organic material. Over the layer of plant material, sprinkle a high nitrogen source. Some sources are: bloodmeal, cottonseed meal, kelp meal or parts of leguminous plants like clover, vetch or alfalfa. Substitute a 1-2″ layer of fresh farm animal or poultry manure if it is available. A complete garden fertilizer, such as 10-10-10 may also be used to supply the nitrogen. One cup for each 25 square feet of top surface area should be adequate.

Next add a layer of soil or sod 1-2″ thick. The soil contains microorganisms that help to start the decomposition process. Use a layer of finished compost if there is not an adequate source of topsoil. Continue to alternate the layers of organic materials, fertilizer or farm manure, and soil. The maximum height is about 5 feet. Air is needed, so do not compact the layers. Water each layer as it is added.


The compost pile must be kept moist for proper heating and decomposition. Too much moisture will bring the composting process to an anaerobic condition, which has an offensive smell. A moisture content from 50% to 75% is recommended for composting in the open air.

It may be necessary to sprinkle the compost if the material is getting too dry. Covering the compost pile with black plastic keeps the moisture loss to a minimum, and helps the moisture loss to a minimum, and helps the decomposition during extremely dry periods. The plastic covering also protects the pile from becoming too wet during periods of heavy rainfall.


Proper temperature is a very important factor. Much heat energy is released by microorganisms as decay occurs. Check the temperature with a thermometer, if available. The experienced composter usually checks the temperature by putting his hand 8 inches deep in the pile. The compost should feel too warm to hold your hand for more than a few seconds in the pile. The temperature of 150°F is needed for killing many of the pathogenic diseases and weed seeds. Failure to reach this temperature might be caused by too much water, improper aeration, too little nitrogen or too small a pile.

Composting Time

Hasten the decomposition by turning the pile regularly. This will help aeration of the pile and reverse any undesirable reactions.

Complete composting can be achieved in about 1 month if the materials are finely shredded and turned at 2 days intervals. Turning the pile monthly will produce compost in about 6 months. The pile should be turned immediately if at any time a strong ammonia or other offensive odor is released. During the decomposition the pile will shrink to about half of its original height. The time needed for decomposition will also vary with the size of the pile and the season of the year.


Because the winter climate in Western Washington is mild, the process of decomposition will continue in fall and winter, but usually at a slower pace. The pile should be made a little larger at winter times.


To maintain the temperature, turn the pile regularly. The wetter the pile, the more frequent the turning should be. If the moisture content seems dry, add water. If adequate space is available, it may be easier to have two bins. Turning can than be done by shifting the entire pile into another bin, and later moved back again. The main objective of turning is to shift materials from the outer parts of the pile closer to the center, where they are better able to heat to the 150°F temperature. This temperature is needed for killing many of the pathogenic diseases and weed seeds. A 150°F temperature, will be reached in the center of the pile by the about the third day after starting the pile.

When to use Compost

Compost is ready for use when the temperature in the compost pile drops to the temperature of the surrounding air. The developed compost should be a fine crumbly, dark mixture. The pH is usually around 7.5. It should have an earthly smell. You can use compost as soon as it becomes ready. Compost stacked in a pile for later use may loose some of the nutrients through leaching. Old compost is still a good soil conditioner even if some leaching out of the nutrients occurred.

Compost Uses

– Mulch around tree and shrubs
– Preparation for new lawns or garden beds
– Screened as a top dressing on established turf
– Starting seeds
– In house plant soil


Composting requires about two cubic feet of equal portions of grass, leaves, plant and vegetable trimmings, all chopped up, moistened and thoroughly mixed to cause the pile to heat. The outside air temperature must be at least 10°C or 50°F. It usually takes 3 to 4 days to heat up to a maximum temperature.


Wet material

Too much fresh fruit skins, rinds, bruised fruit or vegetables.

Solution: Add shovel full of dry soil, shredded leaves or newspaper.

Soggy material

Rain or excessive watering.

Solution: Turn pile to aerate and add shredded leaves or newspaper.


Moist material

Not enough nitrogen material.

Solution: Add nitrogen materials like grass cutting, manure or an organic activator.

Dry material

In direct sun and no new materials added.

Solution: Add enough water to dampen only and add nitrogen material if necessary.