Composting & Organic Waste

Composting is controlled aerobic decomposition - the breakdown of organic matter by microorganisms in the presence of oxygen. Understanding the basic science helps you create and maintain an effective compost system.

The key to successful composting is balancing carbon-rich materials (known as "browns") with nitrogen-rich materials (known as "greens"). Browns include dry leaves, straw, cardboard, sawdust, and wood chips. Greens include fruit and vegetable scraps, fresh grass clippings, coffee grounds, and garden prunings. The ideal carbon-to-nitrogen ratio is approximately 25-30 parts carbon to 1 part nitrogen (25-30:1). Too much carbon and the pile decomposes very slowly; too much nitrogen and the pile becomes slimy and smelly.

Decomposition proceeds through distinct phases. In the initial mesophilic phase, bacteria that thrive at moderate temperatures (20-45 degrees Celsius) begin breaking down easily digestible materials. As microbial activity intensifies, the temperature rises, initiating the thermophilic phase (45-70 degrees Celsius). This high-heat stage is critical because it kills weed seeds, plant pathogens, and many harmful bacteria. Thermophilic decomposition typically lasts several weeks in an actively managed pile.

As readily available food sources are consumed, the temperature gradually drops and the pile enters the curing or maturation phase. During this stage, fungi, actinomycetes, and larger organisms such as earthworms and woodlice colonise the material, further breaking it down into stable humus. The curing phase can last several weeks to months, depending on conditions.

Three factors are essential for healthy composting: moisture, aeration, and particle size. The pile should feel like a wrung-out sponge - moist but not waterlogged. Regular turning or mixing introduces oxygen, which the aerobic microbes need to function. Chopping or shredding materials into smaller pieces increases the surface area available for microbial colonisation and speeds up the process considerably.

There is no one-size-fits-all composting method. The right system depends on your living situation, the amount of organic waste you generate, the space available, and how much time you are willing to invest. Here are the most common options.

Backyard compost bins are the most traditional approach. A simple enclosed bin or open pile in a garden corner can handle kitchen scraps and garden waste year-round. Bins keep the material contained, retain heat and moisture, and deter animals. You simply add a mix of greens and browns, turn the pile occasionally, and harvest finished compost from the bottom after several months. This is ideal for households with gardens, and the resulting compost enriches flower beds, vegetable patches, and lawn soil.

Compost tumblers are sealed, rotating drums mounted on a frame. They are easier to turn than traditional piles (just spin the drum), produce compost faster due to better aeration, and are more resistant to pests. Tumblers work well in smaller gardens or on patios, though they have limited capacity compared to open bins.

Vermicomposting, or worm composting, uses specialised composting worms - typically red wigglers (Eisenia fetida) - to process food waste. Worm bins are compact, odourless when managed correctly, and can be kept indoors, making them perfect for apartments. The worms consume food scraps and produce vermicast (worm castings), which is an exceptionally rich fertiliser. A well-maintained worm bin can process roughly half a kilogram of food waste per day.

Bokashi is a Japanese fermentation method that uses an airtight bucket and a bran inoculated with effective microorganisms. Unlike aerobic composting, Bokashi works anaerobically - you can add meat, dairy, and cooked food scraps that would attract pests in a traditional bin. The waste ferments for about two weeks, after which it can be buried in soil or added to a compost bin to finish decomposing. Bokashi is an excellent option for apartments and households that want to compost all food waste without exceptions.

Community composting programmes serve residents who cannot compost at home. Many European cities have established neighbourhood composting sites where residents can drop off food scraps. These sites are managed by trained volunteers or municipal staff and produce compost used in community gardens, parks, and urban agriculture projects. Community composting also builds social connections and creates a shared sense of environmental responsibility.