Aerobic Decomposition - Give 'em Air

There are two paths your compost can take, aerobic decomposition or anaerobic decomposition.

Decomposition in air, the aerobic type, is the best path for your compost. Your compost decomposers, at least the ones you'll want to have around, need air - specifically oxygen - to carry out their excellent work of recycling, renewing and restoring the world.

Aerobic Decomposition - Yum

If you manage to keep a decent flow of air through your compost the aerobic microbes will thrive and the process of decompostion will be fairly quick. Your materials will break down cleanly into CO2, H2O, minerals and humus.

Your plants will be happy not only with the humus, but also with the types of soil organisms sure to come with it. They will be aerobic and will fit right in with your plants preferred habitat.

Anaerobic Decomposition - Yuck

Anaerobic conditions might occur as your compost decomposes and air is used up, or if conditions are too wet, again excluding air. When this happens the aerobic organisms die and anaerobic organisms move in and take over.

Anaerobic decomposers have a harder time digesting and breaking down material. As well water and some nutrients will be released but along with them come a number of organic acids and amines that are not useful to plants.

Your pile will start to stink as Hydrogen Sulfide (which smells like rotten eggs), putrescine (which as you might have guessed smells putrid) and cadaverine (which smells like a cadaver or dead body) are released.

The decomposition process will also slow down. Decomposition is different - it yields a slimier result and one of the by-products is methane gas, a gas 23 times more potent than CO2 in its effects on global warming. The other thing is that your compost will be loaded with anaerobic bacteria, not your plants favourite friends.

Strategies to Maintain Aerobic Decomposition

Given the nightmarish vision of the anaerobic compost I believe you will want to try to maintain an air flow through your compost, or maintain aerobic decomposition. There are a number of strategies - some requiring muscle, others brains and planning. Here is the short version followed by details:

  • Turning Your Compost
  • Using Compost Aeration Tools
  • Making Air Pockets as You Build
  • Using PVC Aeration Pipes

Turning Your Compost - For the Fit Athletic Types

Many books and articles on composting advise you to turn your compost pile when it cools down and/or when it starts to stink. Turning a pile is done mainly to add air or keep aerobic decomposition processes going. Don't forget when turning the compost to check and make sure the material is moist. If you find dry spots moisten them and carry on. What you want to do apart from adding air is to more or less turn the pile inside out so that what was at the center moves to the sides and the top to the bottom.

Turning compost can be satisfying to those with good strength and endurance. An "officially big enough" pile of a cubic yard or cubic meter weighs a ton or more. A truly energetic person might flip a pile back and forth a couple of times a week and probably most piles would benefit from being turned at least twice.

If you know darn well that you are unlikely to cheerfully shift a ton of material from one place to another, is a stinking mess your only alternative? Of course not. Even the lazier weaklings like myself are able to keep aerobic decomposition fires burning with a few brains.

Passive Aeration

- For Those Who Know Darn Well They Won't be Turning That Compost Anytime Soon

Compost Aerator Tools, Sharp Sticks and Things

I suspect many of us have our compost cleverly enclosed in a fairly small plastic bin we bought at a bargain price from our town or city. The problem with these little numbers is that it's tough to get a shovel or fork into them. If you were to actually turn the compost you'd have to pull the bin completely off the compost and proceed.

Enter the compost aerator. I have one and it works better than I thought it would but...

It is a pole with a pair of collapsing wings at the end. You plunge the pole into the middle of the compost and when you pull it up and out the wings open and fluff the compost thus adding air. It can be hard to get the tool into the compost and sometimes the wings won't open. I think they get bound up with bits of compost.

If you'd like to give it a try you can get a compost aerator through amazon.

You can also use any stick or pole and just sort of stir it around as best you can. This is helpful, but many people would find it hard to do. Also, it does not maintain an air tunnel. The compost closes back in to some extent after the aerator or pole is removed.

Make Air Pockets as you Build

This is something I'm only now beginning to do on purpose. The trick is in the types of brown materials you use to build your compost. Grinding your materials into small bits generally speeds up the compost process, however, there is a place for some rougher materials.

Use rough sticks and stalks as the bottom layer to help with drainage and air circulation. A few rough sticks and stalks throughout your compost will give it some structure. As the compost collapses in the process of decomposition the sticks and stalks continue to hold it up leaving some air pockets intact.

Other items such as toilet paper, paper towel, and gift wrap rolls, as well as paper egg cartons create small tunnels of air wherever they are in the compost. While these eventually collapse they'll maintain air pockets for a good length of time.

Aeration Pipes

Finally, though feel free to send me your solutions, you can use aeration pipes. These could be inserted vertically after the fact. They need to be porous. Some ideas include a tube of wire mesh or a bundle of cornstalks.

A great option is using PVC pipes drilled every few inches with 1/2 inch or 1 cm size holes. Use about 2 inch pipe. Larger pipes have a tendency to cool the pile down too much.

The Open Road people from NYC developed a compost box they call the Hot Box. It's designed to maintain an air flow using a clever system of horizontally placed 2 inch PVC pipes. Three drilled pipes are placed near the base of the bin and a second set of three pipes about a foot or so higher. Research and field tests have shown that this does indeed maintain enough air for aerobic decomposition without turning the compost. Yippee!

  1. Compost Home
  2. How to Make Compost
  3. Aerobic Decomposition