The Organisms in Your Compost

Bacteria

Bacteria are single-celled microorganisms that exist virtually everywhere. In fact, they are inside your body right now, about a hundred trillion of them, or ten times the number of cells you have. (Are you freaking out? Don’t.)

In a compost pile, bacteria do most of the decomposition work. Me­sophilic bacteria chow down on sugars and starches and are most produc­tive in a temperature range of 70 to 90 degrees Fahrenheit. Most backyard compost piles are mesophilic, taking their temperature cues from the ambient air. As mesophilic bacteria eat, they produce heat, and the tem­perature of the compost system begins to rise. If they achieve temps of about 104 degrees, it gets a little too warm for them and their population dies off.

But when a door closes, a window opens, and through it charge heat-loving thermophilic bacteria. These are the dudes behind what you’ve heard of as hot compost piles. These powerhouses survive temperatures up to 160 degrees and plow through proteins, fats, and complex carbohy­drates such as the cellulose in plant matter. Per EPA guidelines, once these sauna-like conditions reach over 131 degrees for three days, the heat suc­cessfully kills off weed seeds and pathogens—two big bonuses that solve problems posed by mesophilic piles.

Eventually, thermophilic bacteria tear through their food supplies, and their activity and population slow until they disappear. The compost’s temperature decreases and another mesophilic phase returns. The cooler bacteria, along with their fungi pals, clean up anything the hot guys left behind.

One particular group of mesophilic bacteria that shows up around this time gets a special shout-out. Actinobacteria, also known by its earlier classification actinomycetes, are a special group of bacteria that appear as a cobwebby, fibrous fuzz. Like fungi, actinomycetes have enzymes that can break down tough debris like stems and bark. If you see some in your compost pile, take a sniff. These bacteria create the yummy smell associ­ated with healthy earth.

Invertebrates

What invertebrates lack in backbone, they make up for in guts. Countless invertebrates, a mix of creepies and crawlies that might otherwise give you the chills, plow through your compost pile consuming organic matter and microorganisms. After this stuff travels through their digestive systems, what’s pooped out is incredibly nutrient-rich matter that breathes life into soil.

Mites, grubs, insects, spiders, and slugs are just some of the inverte­brates that dig through, chew, digest, and mix the material in your com­post pile. But the superstars? Earthworms. It’s possible that you’ve only seen them floundering on sidewalks after a good rain, but in areas rich with foliage like the forest floor, earthworms are essential in transforming organic matter into food for soil.

This process can actually be replicated in containers in your own home using a method called vermicomposting.

Putting it All Together: Cooking Up Compost

Now, back to Ma Earth’s original recipe. You’ll recall it goes like this:

• 1 part nitrogen-rich greens
• 30 parts carbon-rich browns
• Several parts micro- and macroorganisms (species vary based on recipe)
• Water (as needed)
• Air (optional; not needed in anaerobic piles)

In general, too many greens in an aerobic compost pile cause a back­log that microbes and macroorganisms can’t consume quickly enough. This results in the unappealing anaerobic conditions described earlier.

On the flip side, too many browns result in a dramatic slowdown of activity. Without the water and nitrogen offered by greens, there’s little in­centive for fast-working bacteria to move in and do their job. While an excess of browns doesn’t cause any unpleasantness for your pile, it may seem like an eternity before you get any usable compost. As it stands, passively main­tained piles (which you’ll learn about in later chapters) can take months to produce compost. If you fail to add enough greens, it could take years.

In general, finished compost has a carbon-to-nitrogen ratio of 30:1. What does that mean? Every brown and green out there has its own unique carbon and nitrogen content count. Coffee grounds are roughly 20:1; saw­dust is about 500:1.

See where this is going? Numerical brain freeze!

I’d rather eat a pineapple than figure out its carbon-to-nitrogen ratio and how it affects my compost pile’s C:N balance. To make sure my com­post piles are balanced, I follow these simple guidelines:

• Use more browns than greens
• For every handful of greens, add two handfuls of browns.

Remember, it’s always easier to add water to a compost pile than to take it away. Err on the side of caution and be generous with your browns. In time you’ll be able to tell by the look and feel of your compost whether it needs more of one than the other. (Don’t you worry: there will be more on this in later chapters, as it pertains to different systems.)

And remember, if you’re wondering if you’ve hit the right balance, think of Armando the Wrung-Out Sponge. He will never steer you wrong.

More from: Compost City

• The Greens and Browns of Your Compost

From Compost City by Rebecca Louie © 2017 by Rebecca Louie. Reprinted in arrangement with Roost Books, an imprint of Shambhala Publications, Inc. Boulder, CO. www.roostbooks.com