All organic matter will decompose naturally sooner or later. Microorganisms – tiny living creatures invisible to the naked eye – feed on decaying food, plant matter, and other organic materials and help transform them into a nutrient-rich soil additive. Rather than have this organic material sitting all over the place, nowadays we keep it in a container known as a composter – but what is a composter and how does it work?
Nature has been composting since the beginning of time, and many cultures throughout history have embraced the practice. There is even a mention of composting in Cato the Elder’s De Agri Cultura in 160 BCE.
The practice was modernized in the early twentieth century and various methods and containers have been developed since then.
What is composting?
The composting process allows decomposable organic materials to be converted into fertilizer; plant waste is broken down by bacteria and recycled into plant food.
Traditionally, composting involved piling up organic materials until the next planting season, allowing them to decay enough to be mixed into the soil – very little time or effort was involved on the part of the composter.
Farmers over the centuries used their animals’ manure or the waste from their harvests and kitchen tables to help enrich the soil in their fields.
The composting process
Researchers from Cornell University have identified three distinct stages in the composting process:
- In the first stage – which lasts only a couple of days – microorganisms that thrive at 20-45 °C (68-113 °F) begin to break down the biodegradable compounds and the temperature within the compost can quickly rise to over 40 °C (104 °F).
- During the second stage, which can last from just a few days up to several months, heat-loving microbes break the organic matter into finer pieces; in this phase, the compost could become so hot that it might actually kill off the helpful bacteria and it should be monitored.
- In the third stage of decay, which usually lasts several months, the same heat-loving microorganisms will use up the available supply of organic compounds and the temperature will begin to drop, allowing the original type of organisms to resume breaking the organic matter into humus – the organic component of soil.
What can and can’t be composted?
A large variety of organic matter can be composted. These items will biodegrade quickly without causing a strong odour, releasing dangerous chemicals, or spreading illness or disease:
What can be composted
- Coffee grounds and filters
- Cotton and wool rags
- Dryer and vacuum cleaner lint
- Eggshells
- Fireplace ashes
- Fruits and vegetables
- Hair and fur
- Hay and straw
- Houseplants (so long as they carry no pests or diseases)
- Nutshells
- Sawdust
- Shredded newspaper, paper, and cardboard
- Tea bags
- Woodchips
- Yard trimmings including grass, leaves, branches, and twigs
If using an open composter, it’s best to bury food waste within the pile so as not to attract animal scavengers such as rats or raccoons.
There are, however, some items that should not be composted as they may either take too long to decay, create an unpleasant smell, or contaminate the soil with harmful chemicals:
What cannot be composted
- Certain types of tree leaves and twigs such as black walnut
- Coal or coal ash
- Dairy products, eggs, fats and oils, and meat or fish bones and scraps
- Pet waste (including dog and cat faeces and used cat litter
- Yard trimmings treated with chemical pesticides
What is a composter?
Modern compost bins speed up the decomposition process, but they usually require more care and maintenance. They are typically designed to hold in moisture and aerate the organic matter which creates a warm optimal environment for the microorganisms involved in breaking the compost down. They can also help to keep vermin away from the rotting plant matter.
There are many types of compost bins; they can be homemade or store-bought. Composters can be made of ceramic, cinder blocks, plastic, stone, wire fencing, or wood (either branches or lumber).
An important thing to remember if building your own composter out of lumber: you should not use pressure-treated lumber if you’ll be using the compost in a vegetable garden as it isn’t food-safe.
The chemicals in the treated wood leach out into the compost and can be absorbed by the vegetables grown with it- avoid this.
How do I choose the right composter for me?
Most gardeners prefer aerobic composting – which means the organisms that break down the organic matter need oxygen to thrive.
In aerobic composting, the right amount of water should be applied to the correct mix of yard waste and kitchen scraps and the compost will need to be turned occasionally, aerating it.
Some people prefer anaerobic compost – which uses bacteria that don’t require oxygen.
The goal is for the organic matter to ferment and decay, which requires far less effort on the part of the gardener, but generally produces a strong, offensive odour.
Continuous Composters
These enclosed bins allow you to add material at any time and compost is generated slowly, with the finished compost settling at the bottom of the bin.
It can be difficult to stir the compost, resulting in less aeration and a longer composting process.
They can, however, handle a variety of materials and the lid will help to keep vermin out.
These are best for the gardener who would like to toss in kitchen scraps, weeds, and yard waste without maintaining the composter regularly.
Batch Composters or Tumbler Composters
A batch composter is the fastest way to create compost, but it requires the most upkeep.
Each batch of compost requires a balanced mix of ingredients and should be turned daily and checked for sufficient moisture; the compost can be ready to use in as little as four to eight weeks.
When full, the batch composter can get rather heavy and may be difficult to spin.
While one batch of compost is cooking, you can begin to stockpile the ingredients for the next batch in an open bin, pile, or continuous composter.
Some tumblers have two compartments so that two batches of compost can be started at different times.
The batch composter is ideal for gardeners who want more compost quickly and who can maintain the composter daily. Read my article What is a compost tumbler – what do they do? for more information.
Indoor composters
These are a solution for apartment dwellers and allow composting of kitchen waste on a smaller scale; there are several specially designed indoor composters including vermicomposter – worm bins – that are a fascinating way to turn kitchen scraps into compost for houseplants or small gardens. Children especially love worm bins, which make these composters a good choice for classrooms.
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