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Compost: How does it work?

Compost: How does it work?

Ask a simple question…get a long answer! Compost is a miraculous, complex and ultimately essential weapon in the armoury of the organic gardener, and while the stuff itself seems simple if not crude, the nourishment it gives your garden is the product of an intricate reaction, a miracle of biodiversity. The combination of decomposing matter and the moisture/warmth of the environment allows the development of a universe of microscopic cultures that can produce vital nutrients for your plants over time. Achieving the right balance of factors to maximise fertility in your compost is a knack developed over years of composting experience. While your regional climate, garden size and other factors can affect the approach you need to take to composting you will need to carefully consider the needs of your plants the chemical balance required to offer them the healthiest and effective compost you can.

Bacteria are the key to all the wonderful benefits compost can offer your garden. These microscopic critters get to work on eating your leftovers even if they go straight in the bin- however you can make the situation perfect for them by keeping the right kinds of foods (for bacteria) in your compost bin. The magic transformation they kick start hinges on their digestion, and the…ahem, broken down matter they leave behind.

There are actually a lot of creatures eating away at your compost- but the most important ones are bacteria, specifically the small (even by the standards of microscopic bacteria!) ones who first tuck in when you start composting. These tiny heroes will raise the temperature of your compost with their activity and the gas they release, and this attracts larger and larger specimens to tuck into your heap- eventually worms, insects and fungus will also arrive. All of these will contribute to raising the temperature and breaking down the solids. Some compost heaps can get up to 60 degrees Celsius!


Drainage, odour, sunlight, surface and space are all things you will need to consider when picking a location for your compost heap. Light and moisture are especially important to the development of bacteria that will add the maximum nutrients to your compost. It is vital that your compost remains warm but is not too hot- so a shady spot on soil is ideal, this will prevent sunlight from heating the heap too much in summer and drying it out, while situating it on soil will allow excess water to drain and prevent mould.

Meat, bones, and things that might carry dangerous bacteria shouldn’t be composted.

Carbon Nitrogen:

The two fuels that keep the bacteria going and

You also need to keep your compost heap topped up with nitrogen-rich green materials: cuttings and trimmings from your garden, grass being a perfect example. Avoid using too much, as this can lead to an unpleasant release of ammonia gas- while add too little and the bacteria may not be able to speed the process of decomposition by increasing temperature.


Mix your compost regularly with a fork or spade to add oxygen: this is a crucial ingredient for them to do their work. Too little oxygen will lead to anaerobic decomposition (while the kind we want is anaerobic) and this will both smell bad, and slow the process.