What is Composting?

Composting is essentially taking organic matter like grass clippings and kitchen waste and turning it into a nutrient-rich soil enhancer. There are several different types of composting but the easiest and generally most accessible is garden composting.

These days garden composting generally involves a large plastic container with a lid on it which is filled with grass cutting, garden clippings and kitchen waste such as egg shells, tea bags and peelings.

Before the advent of cheap plastic compost bins, composting could have been a pile of garden waste in the corner of the garden but the process is nevertheless essentially the same: organic waste rots and is broken down by bacteria, worms and other small creatures, releasing the nutrients and compounds into a form that plants can easily absorb and use from their roots.

Composting can be enjoyable and rewarding and include the whole family. Whether you are just curious about the process or excited by the alchemy of turning waste into ‘garden-gold’, composting is a great way to help the environment and potentially save money at the same time.

What are the main types of composting?

There are three main types of composting: Cool composting such as the type mentioned above, hot composting such the large scale municipal and industrial type and worm farms.

The large scale composting is done on such a scale that as the bacteria breakdown the organic matter, the heat produced builds up to temperatures 70 degrees centigrade plus. This is what the ‘hot’ in hot composting refers to and this is the quickest and most efficient method.

Worm farms use a high concentration of worms and regular aeration to breakdown organic waste quickly. High temperatures are not achieved and this method can be quite labour intensive as the conditions need to be right for the worms including turning the mixture regularly.

Cool composting or garden composting is the type of composting you can easily do in your garden and the process generally takes about a year to produce good useable compost. There is little maintenance involved in creating compost this way and the plastic compost bins which are most commonly used are available from most DIY stores.

The main benefits of the Hot composting process are the speed and the fact that the temperatures reached are enough to kill off most harmful bacteria and weed seeds.

One of the main problems with cool composting is that as the heap never reaches very high temperatures, weed seeds and bacteria are not killed off as they are with hot composting. This does put slight limitations on the types of organic waste which can be composted in this way; dairy and meat waste, animal faeces and diseased vegetables should not be disposed of in this way.

What are the mechanics of composting?

Composting in your garden is just a controlled version of the same process going on all around us, for example, in gardens and forests. Plants and trees need essential nutrients which can only be absorbed through their roots in liquid or gaseous form and insects and micro-organisms break down organic matter in the soil which releases these nutrients, making them available to be absorbed and used by these plants.

Bacteria use carbon for energy and nitrogen to grow and reproduce. They oxidise the carbon turning it into carbon dioxide (CO₂) and this oxidisation process is what causes the heat build up within a compost heap.

These bacteria also need air and water to thrive. To keep enough air within the compost heap it may be an idea to turn the mixture regularly or add screwed up newspaper which creates air pockets. The moisture content should be close to 50%. Too little (less than 40%) and the bacteria will slow down. Too much (above 60%) and water will fill the air pockets pushing out the oxygen cotentent.

The main source for the carbon or ‘brown’ element are things like woody matter, straw, leaves, newspaper or cardboard and for the nitrogen rich or ‘green’ element, things like grass clippings and kitchen waste.

As a general rule, you should try to keep the green / brown mix at about 50:50.

A very important thing to remember is that if the balance of carbon and nitrogen is badly wrong or there is not sufficient air or water, the bacteria will die and the compost heap will fail.

How do I start composting?

If you now know the basics of composting and the mechanics of the compost heap you should now be ready to start composting.

The simplest and quickest way is to buy a plastic compost bin from your local council or DIY store. They are normally cylindrical and around 1 metre tall.

Place the bin in your garden and simply start putting your kitchen and garden waste into the bin (remembering to try to keep the correct ratios of ingredients).

As mentioned before, there are several things you should not dispose of on your compost heap. The main ones being:

• Meat and dairy products or animal faeces. The temperatures reached are not high enough to kill off the dangerous bacteria present in these waste products.
• Weed seeds. You may end up accidentally spreading these round your garden from within your finished compost as the temperature inside your compost heap won’t kill these.
• Dense woody material. This type of thing can take several years to decompose properly.
• Diseased plants. Again, the temperatures inside your bin won’t kill these harmful bacteria.

Regarding what can be recycled on your compost bin, you can add leaves, grass cutting, plants, slugs and snails from the ‘slug-pub’ (simply a plastic pot which you fill with a little beer once a week - slugs love it so much they fall in and drown), cardboard, newspaper, potato peeling, rotten fruit, mouldy vegetables, horse manure and stale bread, to name a few.

The composting process should take around a year before you can start to use your finished compost.

What do I do with the finished compost?

The ideal time to use your finished compost is in the Spring, before planting, however, there is actually no right or wrong time.

You can dig it into a flower bed to improve the soil or dig it into your vegetable patch or allotment to revive soil.

It can also be used as mulch, spread around the surface of the soil and around plants. It conserves moisture, suppresses weeds and the nutrients will slowly leach down into the soil beneath it.

If you want to use it as potting compost it may be useful put it through a garden sieve it first to remove large pieces before adding equal amounts of garden soil and sand.

Poor quality clay soils benefit much more from large amounts of compost dug in to it over several years