Doing your aerobics

Composting isn't just a case of piling everything up in a heap and leaving it alone. This is the approach many gardeners take, and the results are generally disappointing. Without turning the heap to let air in, the heap cannot break down properly. You are likely to be left with a sticky smelly mess that is quite difficult to work with.

In technical terms the process you want to avoid is called anaerobic decomposition (meaning without air).

To get nice light fluffy compost you need to use a process called aerobic decomposition. Letting air into the heap helps evaporate off excess moisture and lets the "good" bugs do their job.

Color coordination

Traditionally a compost pile is made up of roughly equal proportions of greens and browns. Greens provide nitrogen and include:

  • Grass clippings
  • Most kitchen waste
  • Most garden waste

Browns provide carbon, and include:

  • Newspaper*
  • Cardboard*
  • Untreated wood chips/shavings
  • Dry leaves

*Newspaper is fine to put in your heap because the inks are usually soy-based and will break down. Cardboard is another great addition to get more carbon but use only the basic "brown" stuff, not glossy or laminated material.

Most composting guides stress the importance of getting the balance between greens and browns right, but the home gardener can be left feeling confused by this advice. It is very difficult to know how much of each essential material is going in your heap. For example, did you know that coffee grounds are actually a green material for the purposes of composting? Hedge clippings contain both green and brown material and the ratio depends on the species of hedge being cut. So how does the home gardener get the balance right?

Most home compost heaps lack brown material. Gardeners often lump lawn clippings, garden, and kitchen waste in the heap and wonder why it just turns to a sticky mess. The best approach for 99% of gardeners is to therefore focus on adding as many browns as possible.

You don't have to worry about getting the proportions exactly right, just make sure you don't end up with lots of one type of material and almost none of the other type.

Although it is possible to have too many browns, it is unlikely that you will find yourself in this situation, especially if you put your grass clippings in your heap. Most gardeners should therefore concentrate their efforts on finding brown material to help balance out the greens.

If you do end up with a heap that is not decomposing and you think you have too many browns, just mix another load of lawn clippings through.

You don't have to build your heap all at once, but heaps built quickly will give better results because they heat up and kill weeds and other undesirables. The activity of microbes generates heat and a larger heap is able to trap this heat.

Water water everywhere?

Water is a crucial part of the composting process, but too much of it will choke your heap. It is best not to add any water at the start, as the material you start out with is likely to already have a high moisture content. When you turn your heap you may need to add small amounts of water so that the heap stays damp but not too wet.

It is desirable to keep your heap covered in wet weather because rain will saturate the heap and stop air getting in.

What about tumblers?

There are very few shortcuts to successful gardening, but a compost tumbler might just be one of them. A tumbler usually consists of a large barrel which sits on a stand so it can be easily rotated. The barrel is filled with finely chopped garden waste and then turned every 1-3 days.

Because the action of tumbling the compost lets lots of air into the material, decomposition is hastened significantly. Given ideal conditions the material can become mature compost within just a few weeks.

Enterprising gardeners have been known to make their own tumblers out of old 44 gallon drums. You don't even need a stand as the barrel can be filled up and then simply rolled around on the lawn to achieve the same purpose. The most difficult part of this project is devising a lid that can be closed after the barrel is full to stop the contents spilling out. It is also a good idea to drill some holes in the barrel to let in air (but don't make the holes too large or finer material might escape).