How Compost Works

compostingCompost just happens – it’s a natural phenomenon. If you pile leaves and twigs in a corner of your yard, eventually you’ll discover they have turned into a dark, fluffy, crumbly material: compost. While you can allow compost to happen, you can also help speed things along if you understand the process.

The workers that break down organic matter include microorganisms, fungi, and soil fauna (earthworms, millipedes, ants, etc.). You’ll create compost most efficiently when you design an environment that provides ideal conditions for these organisms.

Normally, decomposition takes a few months to several years. But if you create optimum conditions for the decomposers, you’ll get compost more quickly, maybe in as little as 14 days.

Start With the Right Ingredients

To produce compost, decomposers need four things: carbon, nitrogen, water and oxygen. Offer these ingredients in a balanced way, and you’ll get a quick turnaround from raw materials to finished compost.

Carbon. Materials rich in carbon (called “browns”) equate to energy food for decomposers. High-carbon materials are typically brown or tan, tough, and dry. Examples include corncobs, cornstalks, dry leaves, straw and shredded newspaper.

Nitrogen. High-nitrogen materials (called “greens”) provide protein for decomposers. Many nitrogen-rich items are green and moist, such as spent annuals, grass clippings and garden prunings. Kitchen scraps fall into this category, including non-green things like coffee grounds and eggshells. Although manures or meals (blood meal, kelp meal, etc.) aren’t green or moist, they’re also excellent sources of nitrogen.

Water. Like other living things, decomposers need moisture to survive. How much water is enough? The rule of thumb is to keep your compost pile as moist as a well-wrung sponge. You can water a compost pile if it dries out. Covering a pile with a tarp or using an enclosed container can help regulate moisture.

Oxygen. Your army of decomposing organisms also needs oxygen to function best. As materials start to decompose in your pile, air pockets disappear. It’s vital to incorporate some method to introduce oxygen into your pile. Turning the pile accomplishes this, as do air vents on manufactured compost bins. For homemade compost systems, consider building the pile off the ground – on a pallet or layer of branches. You can also insert one or two pieces of 4-inch perforated plastic pipe into the center of the pile; shaking the pipe vigorously every other week increases airflow into the compost.

When you have the right ingredients present in the right proportions, decomposition occurs speedily. The decomposition process generates heat, which is vital for destroying weed seeds, plant pathogens, and disease organisms. Turning the pile helps ensure that adequate heat is maintained to produce problem-free compost.

Follow a recipe – or not!

The ideal ratio of brown (carbon-rich) to green (nitrogen-rich) materials in a compost pile is 25:1. Compost piles with too much brown and not enough green take years to decompose. Too much green and not enough brown produces a smelly, wet pile.

Achieving a perfect 25:1 ratio isn’t necessary for composting to occur. Remember, it’s a natural process. Try this approach:

  • Layer materials to form a pile, aiming for three to four times as much brown as green. For the fastest composting – called “hot composting” – layer green and brown materials in a 1:1 ratio.
  • Build layers that are 3 to 4 inches thick.
  • Sprinkle a half shovelful of finished compost or topsoil (both contain decomposers) between layers.
  • Water every other layer.