Alison Swanson of the Scottish Allotments & Gardens Society sets out the recipe for perfect compost.

As the growing season slips gently into winter allotments that once burgeoned with produce are now littered with wilting vegetation. This can lead to a touch of melancholy in sensitive souls but for plotters, who are pragmatic by nature, all this plant waste means now is a perfect time to make compost.

Too much is not enough
In scientific terms the wonderful dark and friable stuff called compost is in fact organic material that has decomposed through the action of micro-organisms and bacteria found naturally in the environment. In other words, it is stuff that once lived, has died, has been eaten by bugs and, is no longer recognisable. Plotters can never get enough of it.

Scottish Gardener:

The benefits speak for themselves
Compost is greatly prized for several reasons. First, it contains essential plant nutrients such as nitrogen (N), phosphorous (P), potassium (K) and trace elements and using it on beds and around plants provides these in suitable concentrations. It is impossible to overdose the soil with compost which can occasionally happen with more concentrated fertilisers used injudiciously. Second, compost contains high proportions of humus which improves the structure of soil. Humus is very complicated but in simple terms it can be thought of like a mass of light and strong spongy granules. These have the capacity to lighten heavy clay, to give substance to sandy soil and to improve water retention in all soils. Humus also promotes a crumbly soil structure necessary for good root development and the take up of nutrients.

Scottish Gardener:

It’s all in the mix
There are two methods for making compost, namely the hot method and the cold method. The former produces compost in weeks and the latter takes months. Both methods use the same recipe consisting of a mixture of ‘green’ and ‘brown’ ingredients in a ratio of 2:1. ‘Greens’ are mainly wet plant and garden waste materials such as grass clippings, old stems, potato haulms, and vegetable peelings whereas ‘browns’ consist of dry organic biodegradables such shredded paper, cardboard, dried grass, hay, tea bags and sawdust.

Scottish Gardener:

Compost is cool
The hot method of composting involves building a heap of alternative layers of greens and browns all in one go to form a good sized heap of around one metre cubed in size. Once it has been created the micro-organisms set to work digesting the material and the heap will get hotter. With hot composting it is necessary to keep recording the heap’s temperature with a thermometer every few days because at some point it will start to cool down and the composting process will slow. At this stage the compost should be turned to introduce more air, thus triggering the process to rejuvenate. This business of checking and turning continues till the compost is fully formed. The cold method of composting offers a much simpler approach and is usually the preferred alternative. This involves throwing the brown and green ingredients in a pile as they appear, not worrying about layers, and waiting. Both methods make good compost however because the hot composting process reaches a high temperature it kills weed seeds and plant pathogens. Unfortunately it kills indiscriminately and therefore also destroys good soil biota. Cold composting however keeps the good soil bugs and also has the benefit of attracting pretty pink and stripy brandling worms (Eisenia fetida). These will appear, as if by magic, and their worm casts provide further nutrients for crops.

Avoiding problems
Not much can go wrong with either composting method but a few rules of thumb should be adhered to. Never compost cooked foods, meat, animal matter, pet faeces, or anything that is not biodegradable such as plastic. It is also sensible to avoid composting anything that may contain contaminants such as creosote or lead which could ultimately be ingested by you via any produce grown on it. If compost gets too dry simply add more ‘greens’ and if it gets too wet simply add more ‘browns’. Always locate your heap directly on the soil and whilst an unrestrained heap works just fine, containing it in a simple slatted wooden box made from pallets or similar looks neater and avoids problems with the allotment committee. Finally, to deal with particularly irritating committee members it may be necessary to learn bokashi (a Japanese method of recycling green waste by picking it before turning it into compost.)