Turning

A compost heap looks passive. It isn't. The microbes breaking down your kitchen and garden waste produce heat as a byproduct, and in a working heap that heat is dramatic — the centre can reach 60°C or more. Steam rising when you open the lid or plunge a fork in isn't a quirk; it's confirmation that the biology is running hot.

The problem is that microbial activity exhausts the oxygen around it. A heap left unturned becomes airless at its core, and anaerobic bacteria take over: slower, colder, and responsible for that sour, sulphurous smell. Turning the heap — physically lifting and inverting it so the outer edges move to the middle and vice versa — restores the oxygen, redistributes moisture, and reactivates the fast aerobic decomposition that gets you finished compost in weeks rather than months.

How often, and how to know

There is no single right frequency. A hot, steam-producing heap in summer may benefit from turning every week or two; a cooler autumn heap might need turning monthly, or less. The practical test is temperature: if the heap has gone cold and silent before the material looks broken down, it needs air and probably some moisture. If it smells bad, it definitely needs turning.

Use a fork rather than a spade — you want to lift and open the material, not slice it. Work from the outside in, physically placing the pale uncomposted outer layer into a separate pile or directly onto the cleared base, then rebuilding with that material at the core. It takes twenty minutes and makes a genuine difference. If your heap is in a fixed bin, do what you can: plunge the fork deep and lever, several times around the perimeter.

Steam reappearing within a day or two after turning is the sign you want. It means the aerobic microbes have found their oxygen, the temperature has climbed again, and decomposition has resumed at pace. No steam after several days of warm weather means the heap needs attention — more green material, more moisture, or both.