One of the first choices you need to make is whether continuous or batch composting is best for your needs.
Continuous composting is a technique that works best if you have a steady stream of new material to work with. If you’re composting the scraps from your household, this is probably the system you’ll want to use. You can start with a small amount of compost and a handful of soil (or compost starter). Then, as you get extra ingredients, just add them to the mix. The compost will blend together — fresh ingredients will blend with more mature compost that’s at an advanced stage of decomposition.
As your compost bin starts to fill up, you’ll just want to stop adding to it for the last few weeks while you keep mixing up the materials so that the newest materials can finish breaking down too. Alternatively, you can sift out the unfinished materials with a compost screen, and throw them back into the pile or the bin to finish up.
The other method is called batch composting. If you have a large amount of organic waste (such as a pile of leaves or several bags of yard clippings) it can be enough to fill up your entire compost bin all at once. As the compost decomposes, this pile of compost will gradually shrink. Finished compost often takes up about 30 to 50 percent less space space than the original ingredients. It can be tempting to add additional materials to the batch as it starts to shrink and turn into compost, but if you add additional waste, the entire pile of compost will take longer to finish.
Any composter or compost pile can be used for continuous or batch composting or a mix of the two methods. When a continuous composter fills up, it is often converted into a batch composter. As the ingredients compact down, the compost can be left alone (batch composting) or new ingredients can be added as space permits (continuous composting)
Indoor vs Outdoor Composters
Compost bins come in a wide variety of designs. One of the biggest differences is whether the composter is designed to be used indoors or outdoors. Outdoor compost bins are intended to be placed outside, or in a covered space where odor isn’t important (such as a barn or garage). On the other hand, indoor compost bins are designed with odor controls built in. These features tend to either reduce the size of the composter or drive up its price. Indoor compost bins are either air-tight or include a special filter to control smell. The filters have a limited lifespan and need to be replaced every 6 months to a year. They are often made from activated carbon.
Single vs Multiple Chamber Composters
A single chamber compost bin is the most common. This type of composter has several benefits – large chambers are an optimal size for generating heat, single chamber compost bins have minimal cost, and assembly is usually very simple. On the other hand, single-chamber composters have one major weakness: when the compost bin fills up, there’s nowhere left to add waste while the contents decompose. Often, it requires more than one single chamber composter to run staggered batches of compost.
Multiple chamber composters were created to deal with this problem. They offer 2, 3, or more separate compartments for compost. As each compartment fills up, it’s possible to seal that compartment and keep adding waste to a different chamber. This allows old waste to completely break down in one part of the composter while new waste is added elsewhere. Uninterrupted composting in the full compartments will quickly yield finished humus, while the additional capacity prevents a backlog of raw waste.
Tumbling vs Manual Aeration
Photo found on Flickr.com courtesy of HoyasMeg.
There are many different ways to aerate compost. Most composters are designed with vents that allow air to flow through the bin. Since compost generates heat and hot air expands, composters generate a slight overpressure. As hot air rises from the unit, fresh air is pulled in from below. This airflow doesn’t penetrate very far below the surface of the compost though.
These vents are generally not adequate to aerate the entire compost pile. Some composters only have air holes or small vents, which means that a bit of elbow grease is required to aerate their contents. The traditional method is to use a pitchfork. Digging up the compost breaks up any airless pockets and also helps to blend the contents. This is called ‘turning’ the compost, and it can be hard work. Labor saving compost turning tools are also available, such as compost stirring rods or other specialized compost aerating tools.
Not all compost bins require manual aeration. Self-aerating composters are designed with components that break up clumps and inject fresh air. One of the more popular features is a tumbling bin. Tumbling compost bins are designed with a metal rod through the center that acts as a pivot point. The bins spin around this metal rod, and gravity pulls compost across the metal rod. As the contents of a tumbling composter fall, they break apart against the metal axle and fresh air is blended into the mix. Other composters include fins that stir the compost when it is tumbled or stirring rods that can be cranked with a lever on the side of the bin. Electric and manual models are available.
Compost bins with bottoms vs ground sitting compost bins
Composters usually sit on the ground, so many composters are designed with only sides and a lid. This reduces the weight of the composter and it also allows compost tea to filter into the earth below. Ground sitting composters can help fight erosion. When bottomless composters are placed over sink holes or cracks in the ground, the finished compost will naturally settle into crevices. Composters without a bottom can even be used to help keep underground bulbs warm during the winter and jump start the germination of certain seeds.
Compost piles and trenches
Compost bins make composting easier, but some people prefer to use compost piles or compost trenches. There is no need for a container when composting, but these types of composting require very different ground preparation. Compost piles are built on top of the ground, which should be cleared of weeds or other plants that might intrude. A fully functioning compost pile can get hot enough to sterilize weeds, but piles on the ground rarely reach optimal temperature. They are usually designed to support their own weight, with layers of twigs between other compost. Compost piles occasionally require turning and may need to be watered in dry climates. Compost piles can attract insects, rodents, and larger animals, so they should be located away from buildings and gardens.
Compost trenches, on the other hand, are dug into the ground. Compost pits operate the same way that a latrine or trash midden does, and should be dug at least 3 feet below the surface to keep animals away. Composting is not recommended in areas with bears, and you should check local laws before building a compost pile or digging a trench.
For instructions on building a compost pile, visit our guide: ‘How to build a compost pile’.