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Browns? Greens? Hot? Cold? What the F, compost?

Yep, I feel you. So here’s my semi-scientific explanation of how composting happens, from memory, and a marginal amount of experience. You’re welcome.

Home compost is free fertilizer that makes your plants grow awesomely because it does awesome stuff to the soil. Like what?

• Compost adds nutrients to the soil like nitrogen, phosphorus, potassium, calcium, iron, just about anything your plant might need. Your plants use these nutrients for all kinds of stuff, but short hand is, these nutrients make plants grow to full size and then do all the stuff grownups want to do like have sex and make babies flower and set fruit.
• Compost helps your dirt to hold on to more water without drowning your plants, so if you forget to water for a bit, they’ll have a better chance of surviving. Or so you don’t have to water as often as you would without the compost mixed in.
• Compost acts like life-rafts for beneficial microbes that help your plant to take up nutrients and access water. A compost twofer!
• Compost helps to create air pockets in the soil so your plants’ roots can get oxygen. Bet you didn’t know that one! Plant roots need oxygen. True story. They don’t get it from the leaves (much), they get it from the dirt, and then use it to photosynthesize. Without plenty of air around their nethers, plants die.

All that good stuff. It’s also good because making compost stops you from shipping all that material to the dump, or allowing it to accumulate for 30+ years against your back fence. What? You don’t do that?

So how do you make a happy compost pile or bin that actually results in composted food? You need three ingredients: air; water; microbe food. It helps to know what nature’s objective is, and how nature accomplishes its objectives.

Air

Nature wants stuff to rot. First it wants stuff to have sex and make babies, and then it wants stuff to rot. There’s two top level methods for rotting stuff in nature, anaerobically (without air) and aerobically (with air). We’re talking about the microbes that do the work to make the stuff rot. Do the microbes use oxygen to grow up and make babies divide and colonize.

If you’ve got a wheelbarrow full of dried leaves and rain water (what? you don’t do that?), then microbes that thrive without air are going to be what lives in there to break down those leaves. That’s rotting that happens anaerobically. You probably already have enough experience at life to know that that stinks.

On the other hand, you’ve got rotting that happens in the presence of air (and also water) that smells to most humans like damp earth, or forest floor – because a healthy forest floor is made out of aerobic rotting leaves. There are lots of little spaces and gaps between leaves, branches, and whatnot, and that allows in air for the aerobic microbes to populate your forest floor. The anaerobic microbes are there too, they’ll go gangbusters as soon as it gets waterlogged and some of aerobic microbes die off to make room. But until they do, the aerobic microbes will have the upper hand because aerobic respiration is like eight times more efficient than anaerobic. They can make babies divide that much faster.

Really, eight times?! Yeah, I dunno. I’m not looking it up! But that’s what I remember from high school biology. It was all like, ATP and some jargon. I promised you semi-scientific and that’s what I’m delivering. Point is, if you have an environment with plenty of air circulating around small enough bits of microbe food, you’ll get aerobic decomposition, also known as compost!

Water

You’ve got two basic kinds of aerobic microbes, bacteria and fungi. In compost a lot of these guys are simple, single cell organisms that can’t move around. They need to live in a moist environment or else they’ll dry out and go dormant or die. “Moist,” I said. Too much water, and you’ll end up with anaerobic respiration, which stinks. We don’t want that. You can get water from the tap, or once you’ve started a bin, a lot of the time you get enough moisture from the kitchen scraps you throw in. Weather and the type of bin will affect how much water you need to keep your pile moist. Too dry? Add some water. Too wet? No problem, add some dry stuff.

If you’re pile is too wet, you’ll know pretty quickly. It’ll start to get that pond water smell that no neighbor wants to be smelling over the fence. Take it easy though, it’s no big deal. The aerobic microbes are still in there, they just aren’t in the right environment to do their job, and the anaerobic microbes have gotten the upper hand. Just mix in some dry stuff and pretty soon you’ll be aerobic again. If I had to do this in a hurry, I’d throw in some white rice. It’s dry and it’ll absorb moisture from the pile. Dried leaves and sawdust are also classics.

The funny thing about aerobic microbes and anaerobic microbes is that you have both in your pile. I’ve learned the hard way not to throw halves of fruit peels like orange rinds or avocado peels into my compost tumbler because they’ll fill up with a bunch of compacted materials from the bin and go anaerobic. Same thing happens with egg shells. Crush or chop those up before you throw them in, and you’ll be just fine.

Microbe Food

Here’s where the greens and browns come in: composting microbes need food for energy and to make more microbes. The carbon rich “browns” in compost are the energy source. The nitrogen rich “greens” in compost are what they make more microbes out of. Microbes need three times as much carbon (browns) as nitrogen (greens) in order to make more microbes. Composting is the process of converting browns and greens into partially or fully digested browns and greens plus extra microbes.

Basically, to get your compost pile to compost down, you’re aiming to make an environment in which microbes, single cell organisms that can’t move themselves, can get what they need to make more microbes. Air to breath, water to stay alive, and the right proportion of food to make more microbes out of.

So are all “greens” green and all “browns” brown? Nope, just mostly. Some nitrogen rich brown colored materials would be manure and coffee. And everything green in color actually has quite a bit of carbon in it as well. Some materials can also be brown or green depending on their stage in the life cycle. Whatnow? Yep. Turns out live plants can pull nutrients out of their leaves before they drop them. It’s part of what gives leaves fall color. So if you add green leaves to your pile, they still have all the nitrogen they needed when they were on the tree. If you add natural leaf fall to your pile, the tree already pulled the nitrogen out of those leaves and now they’re carbon rich browns.

Hot or Cold Composting

By changing the proportion of these three ingredients, you can make your compost compost down more quickly or more slowly. Shorthand, this is what we call “hot composting” or “cold composting.”

In hot composting, you’re optimizing your pile to get those microbes to reproduce as quickly as possible. Get this right, and the inside of you pile will be steaming hot. How do you get this right? By making sure your pile has about three times as much browns as greens, in small enough pieces for those microbes to get all up in there (they can’t get themselves inside of a solid branch, but can cover every bit of a dead leaf, which do you think will compost faster?), making sure all that microbe food is moist enough to keep the microbes alive, and then make sure they have lots of fresh air by turning or aerating your compost pile as often as every 1-3 days. Aerobic microbes use up the oxygen in the pile as they grow, so if you don’t get them more, they’ll start to die off, and your compost will slow down and cool.

Microbes are everywhere, so they’ll be in your compost naturally. But if you really want to speed up the process by a couple weeks on the front end, you can buy them in a prepackaged compost starting power. Basically, you add millions of microbes to your pile and don’t have to wait for them to procreate on their own. I’ve tried Jobe’s Organics Compost Starter (check it out on Amazon here). It totally worked. Hot compost in four days. For seriously.

In cold composting, you’ve got your aerobic microbes doing their thang, but you’re also inviting critters like insects and worms to the party. Cold composting is slow. It can take a year to get usable compost, but it’s also much lower maintenance. You still want to make sure that you pile has moisture and air, but since you don’t have a giant population using up that air, you don’t have to turn the pile as often. Also, burrowing critters like beetles and worms will add air to the mix too. This might work better in some climates than in others. We’ve got 100+ degree summers here, so compost piles that don’t get regular love and care (water) tend to dry out. Dry compost material means dead microbes means no compost for you. My MIL cold composts in Norway where spring, summer, and fall are cool and wet, and she’s turned a granite outcropping into an English garden in 35 years.

Both methods are good, some people advocate more for one than the other. Here are some factors to think about as you decide which type of composting you want to try:

• How often do you want to turn your pile?
• How much material do you want to compost?
• How much space do you have for compost piles or bins?

If you have plenty of space or not much compost material, and are in no hurry to turn your yard waste and food scraps into compost you can use, cold composting could be for you!

If you have limited space for composing, have lots of material to compost, want to be able to use your composting in about two months, and are willing to turn it every one to three days, then congratulations! Hot composting is for you!

Think I got something wrong? Maybe. I did this from memory. Hit me up on Twitter @decentmadam, and we can haggle over whether I’ll change it.