How to... make the perfect compost heap
Learn to make your own garden fertiliser
Composting can seem a mysterious business but, once you understand how it works, it's quite straightforward. Thanks to a new generation of super-efficient bins, many previously forbidden ingredients can be composted for the benefit of both your garden and the environment. Get started now and it won't be long before you're digging black gold' into your soil.
The science bit
Every living thing eventually dies, decomposes and turns back to earth. If air is involved in this process - called aerobic decomposition - the bacteria feed on oxygen and the result is a compost rich in nitrogen and other plant foods. A by-product of this is heat, which is a good indicator that the bacteria are hard at work and, as a bonus, kills off harmful bacteria and weed seeds.
The idea of a compost heap is to help decomposition take place in a controlled way. Regular turning incorporates air and reinvigorates the bacteria. If air is excluded, the bacteria are powered by nitrogen, resulting in a compost that is low in nitrogen but still useful for improving soil texture. This is anaerobic decomposition. Both peat and leaf mould are formed this way. So, if you stack your garden waste in a heap and leave it, it will eventually rot down, but it will become compacted with all the nitrogen used up in the process. As no heat is given off, the compost may well be full of weed seeds. Anaerobic decomposition is therefore better restricted to leaves only.
Bays or bins?
There are two ways to go - the traditional route, where you buy or construct a series of bays (ideally three) from wooden planks, pallets or straw bales, or the modern way, using purpose-made bins. These are available from garden centres or your local council, which may provide them at a discount or even free. Traditional bays are generally better for bigger gardens, as having sufficient bins for large amounts of waste could end up looking like a Dalek invasion.
Compost bins are increasingly sophisticated. New from Sweden is the Green Johanna (www.greencone.com), which can be used for a mixture of garden and kitchen waste. It has a vermin-proof base and lockable lid, but should be positioned where it cannot be knocked over by foxes or badgers.
Recipe for success
The ideal mix for compost is 50 per cent dry ingredients and 50 per cent fresh. This is the carbon/nitrogen ratio - newspaper, cardboard, spent potting compost, straw and dry bracken are all carbon rich, while kitchen waste, lawn mowings and annual weeds are nitrogen rich.
Ideally, all the ingredients should be shredded if necessary, then thoroughly combined before they are added to the bay or bin. Although shredded twigs, branches and autumn leaves can be incorporated, the lignins they contain take longer to decompose, so it will be longer before you have usable compost. Avoid the roots of perennial weeds, such as ground elder and bindweed, unless they have been thoroughly dried, and go easy on the citrus, as it can make the compost too acid.
Turn and turn again
The more you turn, the quicker your compost will be ready and the richer in nutrients it will be. Turn or mix it once a week and you can have usable compost in 12 weeks. If that seems hard work, you can get similar results from the rotating ComposTumbler (www.henchman.co.uk). Another new composter, the Earthmaker (www.earthmaker.co.uk), uses gravity to feed ingredients through its three chambers over three months.
The end product should smell earthy and be dark and crumbly with lots of texture and more character than commercially produced soil conditioner. Store it in black plastic bags or a lidded dustbins.
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