Ann Wright: Compost — the gardener’s best friend

Usually at this time in August, Master Gardeners of Nevada County are moving compost from the Nevada County Fairgrounds back to our Demonstration Garden in preparation for our compost workshop. This year is quite different.

Although we are not able to meet at the Demonstration Garden for our compost workshop, we are offering it live online today! Join Master Gardeners of Nevada County on Zoom at 9 a.m. for “Compost is the Gardeners Best Friend.” Go to our website at to find instructions for accessing the free program. The workshop will be recorded, so if you miss it or want to watch it again, the recordings of all our Zoom workshops are on the website.

Traditionally at the Nevada County Fair, our compost display demonstrates the components added to a compost batch pile to produce successful “hot” compost. Nitrogen rich “greens” and carbon “browns” are added to wire enclosures containing the compost. Daily temperatures show how hot a compost pile can be. The sustained heat of a hot batch pile helps to kill pathogens and weed seeds. Last year the compost pile was around 160 F at the center and 141 F about six inches from the edges of the pile. (We will miss not being able to crown a “Compost King or Queen” – the person whose guess is closest to the actual temperature of the pile.)

For those who are not familiar with the process, composting is nature’s way of recycling. Organic waste is biodegraded in an aerobic condition (meaning that it requires oxygen), the result of which is organic matter transformed into a rich substance that can be used to amend soil.

Composted material is rich in microorganisms and nutrients benefitting the soil in many ways. The addition of compost to the soil helps decrease the need for chemical fertilizers and it helps conserve water — compost can retain 100% of its weight in water and is an important consideration to protect our water resources. Overall soil health is improved with composting. The healthier the soil, the healthier the plants. The composting process also diverts kitchen, yard and garden waste away from landfills where the material decomposes anaerobically (without oxygen) emitting methane gas which is harmful to the environment.

The four basic ingredients for composting are greens (nitrogen), browns (carbons), water and oxygen. Greens include things like vegetable trimmings, egg shells, coffee grounds, lawn clippings and animal manure (not dog, cat or human). Browns include sawdust, chopped woody prunings, pine needles, dry leaves, and newspaper. Meat, bones, fish, dairy or grease products should not be composted.

Hot composting occurs when a pile, the minimum of which is three or four feet wide and tall, of mixed greens and browns is combined. This volume is necessary for heat-producing bacteria to speed the decomposition process. Heat can accelerate composting and kill weed seeds and pathogens. The bigger the pile, the more heat-producing bacteria will be present; the smaller the pile, the fewer thermophilic-bacteria. But heat is not necessary for decomposition to occur. “Cold” piles will also decompose, but will take longer.

Water and air are also a requirement for composting. Wet the pile so it’s like a wrung-out sponge. Turning the pile helps add oxygen – particularly if there are dense, soggy areas. If the pile dries out, add water then move the material on the outside edges toward the center to promote quicker decomposition. When the pile stops heating up, allow it to sit for about six weeks. As compost cures particles will shrink, and pH will stabilize, moving closer to neutral. Compost is “done” when the original materials are unrecognizable, and the compost it is dark brown, with an earthy smell.

Once the process is complete (a well-managed batch pile will be ready in two to four months) the compost will be ready for use to build good soil. The best time to top dress or incorporate compost to the vegetable or flower garden is during fall or spring. Compost can also be used in potting soil or for starting seeds. Mix up to 30% compost with other materials such as potting soil, perlite and/or vermiculite. Research has shown that microorganisms found in mature compost can suppress plant diseases such as those causing “damping off.”

Finished or unfinished compost can be applied as a mulch three or four inches thick on the soil surface. Keep compost mulch two to three inches away from plant stems/trunks. Nutrients will filter into soil without robbing nitrogen from the root zone. Compost insulates soil from extreme temperatures and increases moisture retention, while providing nutrients and organic matter for soil structure. Compost is indeed a gardener’s best friend! As we are nearing the end of August, it is a good time to consider compost techniques and allow the heat of summer to help compost process along.

While our office at the Veteran’s Hall is still closed, we are answering questions via our website under the “Got Questions” link under the left navigation menus. We are also LIVE on KNCO radio, 830 on the AM dial – every Saturday from 10 a.m. to noon. Watch our website for more virtual workshops.

Ann Wright is a Nevada County Master Gardener.

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