By Joan Morris

Contra Costa Times

WALNUT CREEK, Calif. — The biology and chemistry of composting is pretty complicated, says Master Composter Linda Mizes, but you don’t have to understand it completely to successfully create a compost pile.

Mizes, a Contra Costa master gardener who also teaches composting classes for the Central Contra Costa Solid Waste Authority, shares these tips.

Simple recipe

A compost bin or pile needs four things: food, water, air and warmth.

The food consists of an equal mix of green and brown material, which feed the bacteria, fungi and other creatures. The BFFs, as Mizes call them, help with decomposition, converting the materials into humus, or soil.

Green materials are high in nitrogen and can include grass, kitchen scraps, manure and coffee grounds. Mizes also puts her weeds into her compost bins, as long as the weeds have not yet gone to seed.

Brown materials are high in carbon and can include leaves, twigs and paper.

Eggshells are neither green nor brown, but they can add calcium to your mix and are OK to add to your pile.

In a drier climate, compost piles and bins must be watered. Don’t drown the mix, though. Your compost materials should have the consistency of a damp sponge.

Air also is essential for the decomposition to take place. Stirring your compost will help aerate it.

There are two kinds of composting — hot and cold — but a certain amount of warmth is required for both. Locate your piles or bins in a sunny spot, especially in winter. Most bins are black to help absorb and maintain the heat in your pile.

Managing your bin

Chop your materials into smaller pieces to help increase the surface area and facilitate the decomposition process. Many plants have a protective cover that resists decay, so cutting them into bits or shredding can break down that cover.

To minimize water and heat loss, pile your materials in a heap, or use a composting bin.

Tend your compost by turning the materials to add air, distribute the moisture and to enhance decomposition.

Monitor the pile for moisture levels and check for surprises, Mizes says, such as mammals moving into the bins to build nests.

You can harvest your compost when about half of the materials have turned to humus. Return the materials not fully decomposed to the pile.

Running your finished compost through a sieve or screen can help remove pieces that aren’t fully composted.

The best way to do this is to pull all of the material out and sift it. Keep the humus and use the rest to start a new batch.