Rex Trulove
There are times when a person might want to have the many benefits of composting and using compost, but they might feel that a conventional compost pile is unsightly, even if they have room for a pile. They might consider an unconventional method of composting; doing it underground.
Pit and trench composting
There are a number of variations to underground composting. However, most use either a pit or a trench. The mechanism is the same in either case.
Pit composting consists of basically digging a hole and putting the compostable material in the hole. Some people take an additional step of using a barrel or similar container that has holes drilled in the bottom and sides. The barrel is then buried and is used to contain the compostable material.
Trench composting is simpler and involves merely digging a trench, filling the trench with compostable material, then burying the compost. This method is better if it isn’t practical to dig a hole that is three or four feet deep. Note: The short video above is a form of trench composting since it is shallow.
Understanding the mechanism
To understand how this works, it can be explained that plant material breaks down naturally because of the action of bacteria, yeast, and organisms such as worms.
In a conventional pile that is four feet high, as the material breaks down, a great deal of heat is produced. It isn’t unusual for a conventional pile to produce temperatures in excess of 140 F. In part, this is because of simple oxidation. This isn’t hard to understand if a person thinks about a fire, which produces heat because of a very rapid form of oxidation. Oxidation, the combination of a material with oxygen, produces heat.
If a conventional compost pile is less than four feet tall, it produces less heat. The plant material breaks down slower because of this. For example, garbage can composting seldom produces temperatures in excess of 80 F. This is called “cold composting”, for obvious reasons.
Aerobic vs. anaerobic composting
A conventional compost pile uses aerobic bacteria to break down the plant material. That is, the bacteria is oxygen-breathing and this is what allows for the oxidation of the material.
This whole process is also responsible for the lack of offensive odors in a properly working traditional compost pile.
Anaerobic bacteria also causes decomposition. These are bacteria that don’t live in oxygen and the lack of oxygen means that oxidation isn’t taking place during the breakdown of material, to the degree found in a traditional pile. Temperatures don’t get high. As importantly, anaerobic bacteria causes foul odors as the material decomposes.
A septic tank is an example of working anaerobic bacteria and the stink this kind of bacteria produces. As it happens, underground composting involves anaerobic bacteria. However, since high-temperatures are not produced, worms and similar organisms do a lot of the work of decomposition. Also, since the compost is covered, bad aromas are normally not very noticeable.
Advantages of underground composting
Unlike traditional compost piles, underground compost doesn’t need to be turned or aerated, though they can be in order to speed up the process. This means that the effort is mostly in digging the trench or pit. Once the compost is added, it is buried and nature takes care of the rest. The compost should be kept fairly moist, but that is simple to do with the use of a sprinkler or similar. This can be an enormous advantage. It is usually less labor-intensive than traditional composting.
The process isn’t a fast one, though. A standard traditional can produce usable finished compost in about two to three months. An underground compost pile can take two to three times longer.
Still, an underground pile encourages the presence of worms, which is helpful for the lawn and garden in general. The worms also produce worm casings which makes the finished compost much richer. Worms can’t live in the high heat of a traditional pile.
Additionally, an underground pit or trench allows for the compost to work out of sight, so it isn’t as unattractive as a traditional compost pile can be.
Underground composting isn’t for everyone, but it is an available option that gardeners can keep in mind. It might even be worthwhile trying both tradition and non-traditional composting so you can see which is the best for you.
I’ve got to find some composting solution. Right now I’m giving my kitchen garbage to a friend who feeds it to her chickens, but I don’t know how long that arrangement will last.
Burying it is one potential solution. You mentioned chickens…don’t forget to include eggshells, regardless of the way you compost. Calcium is one thing that most soil is a bit deficient in and it isn’t a mobile element, so once plants use the available calcium, there won’t be any more calcium unless it is added to the soil. Eggshells is a cheap way to do that.
Don’t worry. I always include eggshells. Sometimes I just scatter them on top of garden. The eggshells have also been proposed as a snail deterrent.
I really enjoyed reading this article, especially your comment about going ahead and planting on top of the underground compost. It seems one could make a sort of hybrid compost pile by digging into the side of a hill, maybe with cascading plants growing down over the opening. It would have some of the benefits of both options.
Doing the composting on a hillside is something I hadn’t even thought of. That is a great idea!
This is a great idea, thanks for the post packed full of information.
You are very welcome. It is a great way to turn marginal soil into rich loam in only a few years, especially if there are trees around. Some people don’t even wait for it to finish composting. They dig a pit, fill it with compostables, cover it with a couple of feet of dirt, and plant on top. Since it is cold compost, it doesn’t burn the plant roots by the time the roots get through the dirt covering.
Thanks again, always good to have choices.