Composting in the Garden

The recent news about recycling in the Gouves Demos got me thinking. Haven’t gardeners been recycling since the year dot? I refer, of course, to composting, which  is the reduction of organic materials to produce useful compost as a soil conditioner or mulch (as opposed to a potting compost – although home made compost could be used as an ingredient of a potting compost).

Many people shy away from composting, thinking that it is some mysterious procedure, shrouded in intrigue and superstition with old gardeners having their own secret formulae and recipes. Let us now dispel some of these myths.

The first thing to realise is, left to her own devises, Mother Nature composts every organic substance (including us) without any help from anyone. Composting is her means of converting spent materials into a food source for soils. All we are doing is concentrating the process into one area of the garden from where we can harvest the produce.

A heap in the corner of the garden will eventually compost. This, however, may take up to two years, so we need to speed up the process providing optimum conditions. Far from a mysterious recipe, this consists of air, moisture, carbon, nitrogen and heat.

These ingredients are controlled by the structure of the bin and the mixture that you add.

A homemade bin has to be built with the aim of ensuring the entry of air into the heap and the retention of heat and moisture. Wooden bins are often built of boards with 2-3cm gaps between them. My own bin is a cylinder of ‘weldmesh’ fencing, lined with cardboard. To help with moisture retention (and to prevent too much winter rain washing away nutrients), simply cover the bin with some old carpeting.

Site the bin on soil so that excess liquid produced in composting process can seep away and soil organisms (worms, bacteria, beetles etc.) can enter the heap to aid the process.

Two types of material are added to the bin. Care just needs to be taken not to add too much of one type of ingredient at a time.

Soft, “green” waste provides the nitrogen to our mixture. They also compost quickly, producing heat and have high moisture content. Examples of these materials are: soft hedge and lawn clippings, raked leaves, annual weeds and kitchen waste (peelings, tea bags, coffee grounds, egg shells etc). Their soft nature does, however, mean that they easily compact and form smelly anaerobic messes.

Bulky “brown” waste provides the carbon for the mix. It also stops the softer waste from compacting and allows air pockets to form. Examples of these materials are: chopped or shredded woody clippings, herbivore animal bedding, straw, crumpled paper, cardboard etc. This coarser material should form between 25 and 50 percent of the mixture. The higher the rate, the slower the composting.

Heat is produced during composting and encourages the process. Indeed, in the centre of the bin the temperature may reach 70c – hot enough to kill many weed seeds and diseases. The bin lid and sides should stop this heat escaping.

What not to add: perennial weed roots, cooked foods and dairy products,  dog or cat faeces, glossy magazine paper, seeding weeds, and, obviously diseased material.

It cannot be guaranteed that all of the heap will attain a high enough temperature to kill off all seeds and diseases. It is better to be safe than sorry.

If you have the time and the energy you may wish to turn your heap periodically. Although not essential, it does speed the process by exposing more of the heap to the high temperatures in the middle, and by opening up any compacted pockets.

As mentioned earlier, my bin is a simple structure to which I regularly add materials. It may, or may not, get turned. In the spring, the resultant, sweet smelling compost is used as a soil conditioner. Any material that has not composted will simply be used to start next year’s bin.