Understanding Compost: What You Need To Know

Compost, compost, compost — any time you talk to anyone about gardening or farming, all you hear about is compost. The stuff seems so important for growing any amount of anything, and it totally is! But what exactly is the stuff that's on everybody's mind?


Compost, in essence, is the product of rotted organic materials that contains many essential nutrients, and has the physical properties of being both airy enough to lighten up compact soil and dense enough to hold water efficiently. Whoosh, that's a lot of stuff! But it's not that complicated. What it boils down to is that compost provides the type of environment that plants crave — like a perfect house for them to live in, or the perfect furniture to complement their existing house. When you've got compost you can grow plants really well, and baby, you can't get enough of it.

Now, when we talk about “rotted organic materials”, we're referring specifically to things that are either found in nature or made by humans, but out of natural materials. Kitchen scraps are a very common thing to put into a compost pile, but you can also put in things like 100% cotton clothing, broken sticks, sawdust, grass from mowing your lawn, leaves from raking, dirt, hair — anything like that. What this also means, though, is that you shouldn't put anything non-organic in your compost pile. This is stuff like plastic, polyester clothing, or motor oil. These things not only won't break down, but they may actually leach toxic materials out into your own pile and, in turn, could poison you or your garden.

So What's Happening In A Compost Pile?

To avoid confusion, it should be noted that the word “compost” is both a noun and a verb — that is, you compost materials to make them into compost. With that out of the way, what's the process to make compost, and what exactly happens when you do it?

The first step in making compost is to get a bunch of organic materials and throw them together into a big ol' pile. There are some philosophies behind the “best” way to pile things up, but there's no wrong way to do it. The process of composting isn't something you can easily stop in the natural world, and to make a compost pile is just to facilitate it and help it along. Trust me, it'll figure itself out.

So, once you have your pile of organic materials, a myriad of bacteria are going to be attracted to it and start breaking down the materials. This is the same phenomenon that happens when you, say, leave a banana out on the counter for too long: bacteria get a hold of it and start eating away at it, causing it to rot. That's pretty much what you're doing: creating a controlled pile of rotting things.

When you have a large enough pile (any amount will do, but the bigger the better), the center of the pile should start heating up. The larger the pile the longer it'll take to heat up, but the hotter it'll get. This heat is good for the compost since the bacteria thrive in a warm environment. The heat also helps to kill off any pathogens or weed seeds that may be viable. If you're throwing your weeds into your compost pile (and you totally should), you don't want to be planting happy, living weed seeds in with your garden next spring.

Now, since the center of the pile heats up more than the outsides, the pile is turned periodically to heat up the outside parts, but also to help incorporate oxygen into the compost. The bacteria that are eating the materials need oxygen to survive. More oxygen means happier, more productive bacteria.

And then, after a few weeks to a few months, you'll have something that in no way resembles what you originally put in. Where did those watermelon rinds go? Where did all that horse manure go? Everything's turned into a crumbly black material, and that's your compost! It's this black gold that farmers and gardeners (not to mention plants) crave.

Carbon vs. Nitrogen

Now, organic materials are made up of a bunch of elements, but two important ones in gardening are carbon and nitrogen. Most everything contains both of these, but some things contain more of one than another. Carbon-heavy materials are usually things like branches, paper, sawdust, cardboard, leaves — anything that's kind of dry and woody. These are referred to as “brown” materials. Nitrogen-heavy materials are things like vegetables, grass clippings, seaweed, blood, coffee, manure — anything that gets kind of stinky when it rots. These are referred to as “green” materials.

When you're putting materials together in a pile to make compost, you typically want a good mix of carbon and nitrogen. Too much carbon and your compost pile will take way too long to break down. Too much nitrogen and it'll get slimy and smelly, attracting fruit flies. A good ratio of carbon to nitrogen (referred to as “C:N” most places) is 25:1 to 30:1 by weight. So if you have a pound of kitchen scraps, mix it in with about 25 pounds of old straw and you'll be set.

This is just the ideal amount, mind you, and it's nothing to stress yourself out about. You'll definitely notice if you have too much nitrogen or carbon. If your compost looks like nothing's going on with it, it probably needs some kitchen waste or grass clippings. If it's wet and smelly and is attracting a lot of flies, throw on some old hay or straw, chopped branches, anything like that. Just try things out! You can't screw it up.

Oxygen is Important

One step mentioned above was turning the compost pile, and this is something that ranks fairly high in importance. The type of composting that most people do is what's called aerobic composting, which means that it is exposed to air. It's similar to people doing aerobics in the 80's — they're doing exercises that get more air into their lungs. The opposite of aerobic composting is anaerobic composting — composting without exposure to air. An example of this is the muck that you find at the bottom of a swamp. The water prevents air from getting to the organic material down there, which is why when you bring a handful of it up it usually smells pretty nasty. That's just different bacteria working its magic, but it's compost all the same!

So when you create a compost pile, you're going to have a big amount of stuff all stacked together. As it breaks down it's going to compact and take up less space. Air won't be able to get into the middle as much, and any nitrogen-heavy materials might start to smell at this point. This is where turning the compost comes in. You want to take the pile and, chunk by chunk, transfer the stuff that was on the outside to the inside, and the stuff that was on the inside to the outside. The easiest way to do this is with a long-handled pitchfork, but a garden fork will work as well.

There are some designs for composters (structures built for the purpose of keeping your compost pile together, although it's fine in a standalone pile if that's all you can do) that have three compartments, all in a row. You start by piling your scraps and what-have-you into the first compartment, then when it's time to turn it you move it all over into the second compartment, allowing you to start a new compost pile in the first compartment again. The second turning moves it into the third compartment, and by the time that stuff is done you should have compost!

Little Critters

Now, when you start creating a compost pile, you're probably going to notice that many little friends are going to take shelter inside of your pile of refuse. Flies, bugs, worms — all of these things are absolutely loving what you've created for them. And for good reason! The warmth of the pile creates a beautiful habitat, and there's practically endless amounts of food there for them to eat.

It may be tempting to get rid of these bugs, but don't do that! They're only helping the process along. You see, it's not just bacteria that are at work in there. In fact, the bacteria are just the first step in the entire process. Worms, for example, happen to be one of the best things for compost. That's because they crawl their way through the pile, creating little tunnels for air to get into. When the bacteria has reduced your carrot peelings down to a slimy goop, they eat that goop and create what's known as vermicompost. Vermicompost is just a fancy word for worm poop, and it's probably what the majority of your finished compost is going to end up being. In fact, most of the dirt where any sort of plant grows is probably poop of some sort. That's one of the beauties of how so many different species survive on this earth. New food has to come from somewhere, so it ends up coming from what the old food has turned into.

Things To Avoid

Now, I know that I mentioned that all organic materials can be composted, and this is certainly true, but to an extent. There are some things that are recommended to avoid composting in your normal bin or pile, especially if you live in an urban area or someplace that's fairly popular.

Meat, dairy, and bones are typically recommended against because when they rot they usually attract flies, which in turn produce maggots, and those things attract specific bacteria. Maggots also cause rotting meat to smell badly, which is an offensive smell to humans. Also, the poop of animals that eat meat (e.g., dogs and humans) is recommended against for the same reason. Poop from vegetarian animals, like cows and horses, is usually fine.

Another reason to avoid putting human poop into your normal compost is that the poop may contain what are known as pathogens. A pathogen is a thing that can cause disease, and some of them can't be killed by the temperatures that compost reaches when it heats up. This means that if you spread compost with pathogens onto the soil that's growing tomatoes, those tomatoes may become infected with that disease, which would be transferred to you when you eat them.

Human poop, of course, is different from human urine. Human urine is actually sterile and is a good source of nitrogen. If you've started off a compost pile and you want to give it a little kick start, go ahead and pee on it. The bacteria inside will thank you for it.


So that's it! What are you waiting for? Composting is easy-peasy and it's a wonderful way of reintroducing nutrients back into your soil that costs you literally nothing. Start a compost pile or grab a bin, throw some stuff in, and watch this magical process take place. I guarantee you'll love it!

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