Recycling – Composting Conditions and Requirements

Recycling – Composting Requirements

All composting methods are designed to meet the needs of the organisms and micro-organisms that decompose, organic matter. They need a varied diet which is balanced in protein and fibre — nitrogen and carbon — and they need air, moisture and warmth.



If there’s insufficient air in your heap aerobic bacteria and soil organisms will die off, but there are plenty of ways to keep a compost heap well aerated. You can simply introduce air by turning your pile regularly, the more frequently you turn it, the quicker materials will break down. But this is not always practical, particularly in a sizeable heap, so you’ll need to look at other methods.

composting-conditions-and-requirements Maximum aeration usually means fastest decomposition, so if you are at all impatient you’ll need to keep helping your heap. You can place layers of pipes or thin poles at intervals through a heap and take them out as the compost gradually heats, or use organic matter for the same job. The soft centres of sunflower stalks rot away quickly to leave hollow tubes, so keep some stalks whole and layer them through the heap every 20cm or so. Jerusalem artichoke stalks do the same job.


Building air circulation

Some composters build off the ground, with wire mesh at the base, collecting any liquids that drip through and recycling them into the container, but it is much better to build a compost heap on the ground so that soil organisms can get straight in. In this case start with a layer of branches and twigs around 15 cm deep. This will be slower to decompose than softer materials above and will allow some air to circulate from below. Keep materials in the heap above fairly well shredded so the mass doesn’t pack down too tightly and air can penetrate, and make sure you never add layers of over-wet or over-dry materials.



Good compost should be slightly damp, like a wrung-out sponge. If the heap is too dry decomposition will be slow and the heap won’t heat up. But if it’s too wet air will be driven out of the heap, organisms won’t be able to work, and you’ll end up with an anaerobic smelly mess with most nutrients washed away.

The trick is not to add too much wet or dry material to your heap at any one time. Always leave very wet stuff like farmyard manure or fresh grass mowings to dry slightly before it goes on the heap, and mix any wet kitchen scraps well into the heap. Dry materials such as hay and straw should be chopped or shredded then watered well before you add them.

If your heap gets a bit wet you can mix in dry straw to take up the excess moisture — dried grass clippings are also absorbent. If it tends to dry out, moisten it with water (or urine which also speeds composting), or with compost, manure or leaf tea.

Protect a heap from excessive rainwater by covering it. Polythene is fine as long as it doesn’t touch the heap, and you could remove it every so often to be moistened by light rain. Cardboard or old carpet are fine if you don’t mind their appearance. A thick covering layer of hay makes good insulation as well as a good water repellent. Don’t leave your finished compost uncovered or nutrients can leach out in rainwater.



Even cold temperature bacteria will be reluctant to get to work if temperatures drop below 13°C, so your heap needs to be well sited and reasonably insulated. Don’t put it in an exposed area or where it is subject to crosswinds, and if in doubt you’ll need to cover it well and insulate it with a straw bale surround or similar. Insulation will also help prevent the heap from drying out.

The size of your heap will determine how well it keeps its temperature. If it is too small the heat released by organisms will disappear quickly and it will never reach optimum temperatures; if it is too large it will take ages for you to get finished compost and the outer edges will stay cool. An ideal size for most home composting is at least im square. If a heap this size is properly built and insulated bacteria should keep on working even in freezing weather as they will maintain the internal temperature.


Carbon/Nitrogen ratio

If you provide your composting organisms with plenty of material, air, water and warmth, you should have no problems. But you also need to keep an eye on the proportions of fibre to protein that you add.

Decomposers need carbon (from fibre) for energy, and nitrogen for protein. If there is too much nitrogen in the pile, then it is released as ammonia or other gases from the breakdown of the proteins in which it is stored. If there is too much carbon, it will take a population explosion of bacteria to decompose it, and they will use up available nitrogen for their own development, causing a shortage. They’ll give it back eventually, when they die, but in the meantime nitrogen starvation means uneven decomposition. The same nitrogen starvation can also occur in the soil when you dig in living compost or fibrous mulches. Well-rotted matter is easily assimilated.

Garden and household waste will probably initially have an average carbon/nitrogen ratio of about 60:1 compared to the 10:1 of fertile soil. If the fibre seems to be breaking down very slowly, add materials with a lower C/N ratio to speed up the process; but if the materials reduce too fast add bulk with a higher ratio.

10. December 2010 by admin
Categories: Compost Making, Soil Cultivation | Tags: , , , | Comments Off on Recycling – Composting Conditions and Requirements


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