Fertilizer Friday -- Composting V - Aerobic vs. Anaerobic

It's Friday, and that means a visit to Fertilizer Friday over at Tootsie Time.
Check out her blog party and see what other people have blooming in their gardens.


This is number five in my series about compost, you can read the others here:
A step by step tutorial for the beginning composter.

Composting I -What is Compost?

Composting II -Getting Started

Composting III -What to Compost

Composting IV -pH

Composting Q & A

Today we are going to meet two of the main organisms that help make compost.

Two different types of Bacteria. Aerobic and Anaerobic.

Both are composters, they will eat organic matter and turn it into compost, but they work differently and each do best in a different environment.

Anaerobic bacteria thrive in water . They are the bacteria largely responsible for composting algae at the bottom of lakes ,and for composting in swamps, bogs and other wet places. Some anaerobes do not like air, while others simply do not require air to live, as a result, they do their best work in places where there is no air. They have a slower metabolism than aerobic bacteria, and take much longer to convert a pile to compost than aerobic bacteria will.

When you hear talk of Cold Composting, it is anaerobic bacteria who do most of the work. The upside of cold composting, or anaerobic composting is that the pile is much less labor intensive. You simply pile everything in a corner somewhere, and a year or so later, you have compost. An additional benefit is that these bacteria have a tendency to reduce the overall size of the pile less, so the same amount of raw material cold composted will produce more humus than it would if it were hot composted.

The downside is that it takes a lot longer, and anaerobic bacteria tend to give off a nasty smell we often think of as swamp gas.

One way to combat the smell is to cover the pile with dirt. If you are composting primarily to reduce your contributions to landfills, cold composting or anaerobic composting is a good solution. You dig a hole, throw everything in and bury it. Or, as an ongoing operation, dig a trench and fill it in, covering it as you go.

In a few years, there will be no evidence that anything beside dirt was ever there.

Aerobic Bacteria on the other hand, require air to live and grow and do their job. Just like a gym full of people working out, they generate heat, so Aerobic composting is what we call Hot Composting. It is the fastest way to make compost.


In order to keep aerobic bacteria happy, you need to keep the compost pile moist but not waterlogged, imagine a sponge that you get wet, then wring out. That’s how wet your compost pile should be.
You also need to make sure they get air. There are several ways to do this.

The easiest way is with an aerator. You can buy a fancy-shmancy one for $35 from the garden store, or, you can use a stick. You poke a whole bunch of holes down through the compost to let air get in.

I cannot stress enough that composting doesn’t have to be, and should not be, an expensive endeavor. There are people who will sell you everything from a fancy bin, to a compost fork, to an aerator to a compost thermometer, compost activator, and a variety of other compost implements, but you don’t need any of those things to make compost.

My preferred method of aeration is to turn the compost. This isn’t necessarily easy, it takes time and it can be a lot of work. But that’s why I have a two compartment compost bin. I take it, one shovelful at a time and move it from one side of the bin to the other, The stuff I scoop from the outside, I toss toward the center and the stuff from the center I toss to the outside, so it all gets rotated.

All the experts say use a pitchfork, but I don’t have one. I do have a shovel, so that’s what I use.

I like this method because it gives me a chance to see how everything is doing. If there are any big chunks or clumps that need to be broken up usually a good whack with the shovel takes care of them. And it lets me see if I need to add water.

I can also check from time to time to see if it is hot, while I am turning it.

Funny that I should mention this, after my mini rant about buying things, but I ordered a compost thermometer from Amazon recently, with an Amazon gift card I got for participating in a study group, so I may not have to keep sticking my hand in it any more. It is a convenience and didn’t cost me out of pocket, but it is not a necessity and nobody should think they cannot compost without one.

Your compost should be between 110-160 degrees F. 110 degrees will feel warm to your touch, but not hot. Imagine the temperature of a baby bottle. or the temperature of the water when you bake bread.

When it drops below 110, or no longer feels warm to the touch, it is time to make some adjustments. If you can still see big pieces of your browns, it means your greens have done all they can and you need to add more. If it is dry add a little water, if not get some air into it.

All those things can be checked while you turn the pile.

Some compost zealots advocate that you turn your pile every day, but the most efficient composting occurs at 130-160 degrees. It often takes a day or two to reach those temperatures, so if you are turning every day, you will cool off your compost, and it will never reach the ideal temperature. It will still compost eventually, but not as fast.

There is no magic formula for time and temperature to make compost, like baking a cake. But you will have compost most quickly if you keep your pile moist and aerated, and keep a good balance of greens and browns.

This will keep your pile aerobic, maintaining the most efficient bacteria for compost. If it gets too wet, and anaerobic bacteria develop, you will notice a swampy smell coming from the pile. The best way to counter that is to get dry material, preferably browns at this point, and air into the pile.

With an efficient aerobic pile, in anywhere from six weeks, to six months, you should have finished compost that is ready to use for a whole bunch of garden needs. The time is influenced by what you put in the pile, some things break down faster than others. Think, Overripe banana, underripe apple, which one will break down first?

Time is also influenced by how big the pieces are. If you blend your greens, and run your browns through a shredder, they will break down faster than if you just chop them and throw them in.

A final factor? Many people suggest "lasagna composting" where you layer your greens and browns, this is a great way to start a pile and a good way to make sure you are putting in even amounts of greens and browns, but if you mix them together in a bucket or wheelbarow before you add them, they will break down faster.

So now we have addressed the last part of FAT TOM, Time, Temperature Oxygen and Moisture.

Next time we will talk about what to do with all that compost once you make it, and I'll reveal an I-knew-better-but-did-it-anyway moment from my compost experience this year.

We were able to finally get the tiller into our garden and run through it, but the ground was still pretty wet and clumped up pretty good, so it is not quite ready to plant, I'm hoping that with some sunshine and wind, it will dry out enough so that we can run the tiller through it again this week and maybe be able to plant it soon.

It was so discouraging to see our plans for a big garden this year all wash away, but we have all summer to build the ground up, dig some drainage ditches and take some other steps so that next year we should be all ready to plant the garden we hoped to plant this year.

Be sure and join me each Tuesday for Tuesday Trivia Tie-in, where readers are invited to share trivia and show off their treasures.

Read all about it here