Using compost before it is ready can damage plants. Undecayed “brown” materials in the soil can temporarily reduce plant available nitrogen. Undecayed “green” materials can harbor pests and diseases. Immature compost can also introduce weed seeds and root-damaging organic acids.
Compost is ready when:
Compost can be shoveled out of a pile or bin and used just as is, especially for mulch. Remove undecayed objects by sifting them through a screen. If you are using compost in preparing soil for planting or sodding, sift it through a one-inch mesh screen. Compost used in potting mixes or as top-dressing on lawns is commonly sifted through a 3/8-inch or 1/2-inch mesh screen.
Make a simple screen by mounting hardware cloth or other durable wire mesh in a sturdy wooden frame that will fit neatly onto the wheelbarrow or other container into which you will screen the compost. Spread compost onto the screen in a thin layer and shake it. You can work the finer material through the screen with a paddle if it is clumpy. Add the oversized material that remains on top of the screen to a new pile to help it start composting faster.