Gardeners talk a lot about compost, and how it benefits us all. Making home-grown compost sounds like a lot of work. But if one thinks about it, having a place to dump leaves, garden debris, manure, grass clippings and kitchen scraps can be downright rewarding – and helpful – particularly when the finished product is so useful.

Finding the place to build a compost pile, or to put a compost bin is a start. Think about the organic material (browns and greens) in your yard that you can use to compost, add a compost thermometer to the list, and you’ll be ready to start. Some examples of compostable browns include: dry leaves and grass, straw, woody prunings, coffee filters, eggshells, and shredded paper bags. Green material may include: vegetable and fruit scraps, fresh grass clippings, wilted flowers, coffee grounds, young green weeds without seed heads or other green clippings from the garden. Items that should not be added to the compost pile include: wood ashes, seed bearing weeds or invasive plants, diseased plants, animal products, dairy products, or cat/dog feces. Likewise, grease, fat, oil, or sawdust from treated lumber or plywood should not be added. For a more complete list of things to compost, check the compost section on our website and the browns/greens list https://ucanr.edu/sites/ucmgnevada/files/192648.pdf .

Once the setup is ready and the pile is built (it doesn’t have to be complicated – a simple pile of leaves will actually decompose) the work is turned over to the numerous little creatures that get the ball rolling, compost-wise. The larger macro-organisms include sow bugs, beetles, ants, centipedes and earthworms. These are the grinders who tear, chew, pulverize and mash materials into smaller pieces. Once the material has been worked by the macros, the microorganisms (the ones we can’t see) continue the decomposition process. Bacteria, fungi and thread-forming actinomycetes are responsible for the majority of the breakdown of organic material. The microorganisms in a compost pile are considered chemical decomposers, because they use chemicals in their bodies to break down organic matter. The result of this process is heat, which is why compost piles heat up.

In order for the “mighty “M’s” (macro and microorganisms) to turn organic material into compost, they first need plenty of material to decompose. Typically, this includes a mix of carbons (browns) and nitrogen (greens), along with water and air. By keeping the mixture damp, similar to a wrung-out sponge, and adding a variety of sizes of material like twigs, stalks or straw to create air pockets, decomposition is faster. Also, the composting process will be slower or faster, depending on the amount and type of the compostable material. For example, by mixing 1 or 2 volumes (say, a large container or a wheelbarrow full) of browns with one volume of greens, and keeping it aerated by routinely “turning” the pile and adding water to maintain it, a rich, finished compost may result in less time than a pile just left to decompose without intervention. Typically, the slower method may take 12 to 18 months to process finished compost. The faster, “hot pile” method — where temperature and amount of browns and greens are monitored — may take 6 to 8 weeks. With this method, as the compost temperature (at the center of the pile) goes up, bacteria begin to feed on nitrogen-rich, green material. These bacteria thrive at temperatures between 120 to 130- degrees F. Science has shown that temperatures above 135 F kill weed seeds and pathogens in the material. But, if the temperature goes higher than around 155 F to 160 F, the heat kills the decomposing bacteria and the process comes to a halt. The optimum temperature for a hot compost pile (meaning “faster” decomposition) is between 100 F and 150 F.

Finally, finished compost is the material that can then be used to amend the soil – whether in garden beds or containers. The addition of compost helps promote healthy soil by retaining moisture, adding enriching nutrients to the soil, and supporting beneficial bacteria that breakdown organic material to further the process. Finished compost is a lovely, crumbly brown material with an earthy odor. Gold, to gardeners!

To learn more about composting, join the Master Gardeners of Nevada County for a free outdoor workshop, “Compost – Good for You, Your Plants and the Earth” to be presented at the Demonstration Garden on the NID grounds (1036 W. Main Street in Grass Valley) – Saturday, September 10, 2022 from 10 a.m. to noon. The workshop will include how to maximize your use of free raw materials, the basics of cold and hot composting, tools to make composting easier, and more. Check our website for more details, https://ncmg.ucanr.org/ .

Ann Wright is a Nevada County Master Gardener

Gardeners talk a lot about compost, and how it benefits us all. Making home-grown compost sounds like a lot of work. But if one thinks about it, having a place to dump leaves, garden debris,…

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