Composting Yard Waste

August 17th, 2021

Composting Yard Waste

by C.R. Wilson and J.R. Feucht 


All yards produce waste from pruning, lawn mowing, and other routine plant care activities. Composting is a way to reduce the volume of organic wastes and return them to the soil to benefit growing plants. 

Organic matter improves the drainage and aeration of clay soil. Compost can be thought of as a separator that “shoulders apart” tightly packed clay particles to allow water and air to enter. Composting helps sandy soil hold water and nutrients. Compost holds moisture “like a sponge” and releases fertilizer nutrients slowly. It also increases the activity of earthworms and other natural soil organisms that are beneficial to plant growth. Note: Compost is a soil amendment, not a fertilizer. It contains limited plant nutrients.


Making Compost 

To make traditional compost, alternate different types of shredded plant materials in 6- to 8-inch layers. Layering helps compost reach the correct nitrogen balance. Use equal parts by volume of dry and green plant materials in the overall mix. Use caution when you add layers of fine green plant wastes such as grass clippings. Grass mats easily and prevents water from moving through the mass. Use 2-inch layers of fine materials or process them through a machine shredder. Alternate fine materials with woody plant prunings to prevent clogging the machine and to create an equal balance of dry and green materials. 

Traditional composting includes soil as one of the layers. While soil can serve as a source of microbes to “inoculate” plant wastes, research has found that the microorganisms that break down plants also are present on the surface of the leaves and stems. It’s natural for some soil to cling to pulled weeds and uprooted vegetable and flower plants. When you add large amounts of soil, you increase the weight, which makes composting difficult and less efficient. Large amounts of soil also can suffocate microorganisms. Soilless composting is often practiced. 

Add water to the compost after every few layers of material. If the plant materials are dry and no green material is available, add a small quantity of blood meal or a commercial nitrogen fertilizer free of weed killers. One-half cup of ammonium sulfate per bushel of material is sufficient. Livestock manure also can be added and supplies some nitrogen. Like soil, manure adds weight and bulk. The space devoted to manure could be used to compost yard wastes. 

There is no advantage in adding compost starters or inoculum to the compost. The microbes that cause decomposition multiply just as rapidly from those that are naturally found on the plant waste.


Compost as Soil Amendment and Mulch 

Mix soil amendments well with the soil to separate clay particles or hold water in sand. For this reason, prepare soil before planting lawns or trees. Areas planted every year, such as vegetable or annual flower gardens, can accept frequent applications of compost. Indoor potted plants and outdoor container plants benefit from compost as an ingredient in potting soils. As with peat-based mixes, potting soils that use compost require a material such as perlite to avoid waterlogging. Some weed seeds can survive composting, but weed plants can be easily pulled. 

Mulches suppress garden weeds, cool soil, conserve moisture and reduce soil erosion. To mulch, apply a 4- to 5-inch layer of organic material on top of the soil instead of mixing it into the soil as with amendments. 

Compost can be used as a mulch. It has the disadvantage of being light and easily blown away in the wind, unlike bark or rock mulch that stays in place. Like any organic mulch, compost supports weed growth, which can cause problems if weed seeds blow into the area. While mulches eventually become incorporated into the soil, amending the soil directly with compost is a better solution where soil conditions limit plant growth.