Urban Garden CenterUrban Compost Tumbler


Too often we hear from people new to composting that "my composter is not working, maybe I should buy another," or "maybe your composter just does not work." Well they are half right. Composters do not work… it's the microorganisms in the compost that do the work. It is not about what composter you build or buy, it is more about microbiology. It is about science. Whether you create a compost pile, build a composter, buy a bin, get a compost tumbler, or put the material in the trunk of your car… if you create a healthy environment for the microorganisms to grow, you will get effective composting. If a healthy environment does not exist, then neither does healthy compost.

A composter is just a container for material and a tool to help create the most favorable environment for microorganisms to work. Doing that sometimes becomes an art but it must still be based on science. The design of a composter only matter to the degree it makes it easier to create a favorable environment for microorganisms, and thereby creating good quality compost, which in turn, encourages people to compost more. The composting effort is only effective to the extent a person follows the rules for the care and feeding of microorganisms. It is up to you to get good compost results.

The Urban Compost Tumbler (UCT) is specifically designed to bring the best features into play for a single small batch composter. It is in fact the best tool available in providing the opportunity to create a good environment for microorganisms.

Understanding the type of microorganisms involved in composting is important because they will really affect the outcome of your composting efforts. There are two basic types: aerobes and anaerobes. The most efficient are aerobes as they work much faster and harder than lazy anaerobes. However, they are much pickier about their environment and if conditions are not just right, they either do not develop or they die off leaving you with just anaerobes. The anaerobes will live and work through almost anything but can take a much longer time to get the job done. The key to rapid composting then is creating a healthy environment for aerobes.

The following components are essential to creating a favorable environment for aerobe microorganisms. These are also the five (5) areas the Urban Compost Tumbler (UCT) is specifically designed to address.

1) Material, 2) Moisture, 3) Temperature, 4) Oxygen, 5) Time

1) Material
Material is made of up of carbon (Brown stuff) and nitrogen (Green stuff). Nitrogen gives the microorganisms energy and carbon is what they eat. While it can vary based on the material, a 25:1 to 30:1 (C:N) ratio of carbon to nitrogen is considered a good starting point. Particle size is also important. The smaller the size of the material, the more surface the microorganisms can get to. Give the aerobes too much energy (nitrogen) and you can burn them out pretty fast. Don't give them enough food (carbon) and you starve them to death while degrading the quality of your compost. Mixing the right variety of materials will enhance compost quality.

2) Moisture
Moisture is the primary transport mechanism for microorganisms, but it also softens material. Lack of sufficient moisture prohibits microorganisms from traveling through the material to grow and work. Too much moisture and they get lost or drown. Compost material should be as damp as a wrung-out sponge and feel wet, but you should not be able to squeeze out water. Use rain water if possible when you need to add moisture to your compost. Municipal water is fine but remember, it is treated to kill microorganisms. Although the chemicals are in small quantities and will evaporate, it is something to think about.

3) Temperature
There are two temperatures to consider in composting; ambient (outside) and composting (material) temperatures. Once the outside temperature drops below 50 degrees F composting really begins to slow down and when it gets below 40 it is practically stopped. Temperature of the compost material itself is important and is a good indicator as to the health of your aerobe microorganisms. Heat generated in the composting process can (and should) easily reach 130 degrees F and is produced by the activity of the aerobes. The initial period of heating may only last a few hours but is important. The faster the aerobes consume nitrogen and eat carbon, the hotter the compost becomes. Hence, if your compost stays cold all the time, the aerobes are not working very hard and will let the anaerobes take over a lot of the work. The result will be compost that takes longer to create. Compost that heats up properly not only composts faster but is higher quality as it can help kill weed seeds, root structures, and pathogens. There is a big difference in both approaches and results as to whether you do COLD or HOT composting. Typically COLD composting is when you keep adding material over time. HOT composting is where you are putting a BATCH of material together all at once. While both approaches work, COLD is more practical for many people but HOT is more effective.

Mass is another important fact that people do not realize affects the composting process. To get effective heating you must have a critical mass of material. In general, material mass with less than 9 to 10 cu ft in an enclosed composter are going to have a harder time heating. Some of the composters on the market today are less than 7 cu ft in capacity and simply are not going to heat well at all. They will still compost, but you are not going to get enough mass to really heat the material.

4) Oxygen
Anaerobes do not need oxygen - this is why they have little energy and are lazy and slow. Aerobes are like you and me; they must have oxygen to work and play well. When you put your material together (your recipe) and start composting it can take only a few hours to burn the oxygen out of the core of the material. When this happens the aerobes sit back and wait until you give them more oxygen. This makes aeration of your compost critical if you want to keep these guys working. Remember, their working is where you get your composting heat and faster composting. No oxygen… no work… no heat. In large compost piles they frequently drive aeration tubes into the core to help get them oxygen. The Urban Compost Tumbler has a built in aeration tube in the center for this purpose.

5) Time
There needs to be a qualification here as to how long it takes to produce compost. You hear many composter manufacturers making claims they can produce compost in a couple weeks. The qualification is that you can spread it on the ground and use it before it becomes fully matured compost. The concept behind backyard compost bins and tumblers follows the 80/20 rule. Get 80% done in the composter and let the last 20% finish in the ground, container or pot. With the proper material mix you can produce compost in a couple weeks (80% done) if you understand that it could take the better part of a year to "finish" the last 20% in the ground. This is an extremely effective method for composting at home and cut the waste stream to landfills. Composting faster like this avoids waiting up to a year for "finished compost" in each batch and makes it easier to recycle yard and kitchen waste into organic compost. Turns out, this is works great for most people.

For more detail information on composting see our Guide to Small Batch Composting