Compost – bins and tips

Compost Bins

Compost can be made in a variety of containers. The examples below show a double bin made from recycled timber, a double bin made from recycled, heavy gauge bird wire covered with knitted polypropylene shadecloth, and a commercial single bin. Double or triple bins are best as you can turn the compost from one bin into the next, with the third bin used to start a new heap.
dblcompost compostbins2
Compost tumblers (below, right) do the work of aerating the mixture. They are suitable for composting small quantities of fairly soft ingredients quickly, for people who are not able to turn compost easily, but the mixture may not generate enough heat to kill diseases.
SAMSUNG DIGIMAX A503 SAMSUNG DIGIMAX A503
Homemade containers don’t require skilled carpentry. What goes into the compost container is more important than how it looks. The main points to remember in deciding on the size and site of your compost container are:

  • When ingredients form one cubic metre (i.e. 1 m. x 1 m. x 1 m.), aerobic bacteria will generate enough heat to kill diseases and weed seeds.
  • Open-base bins that are in contact with soil allow earthworms to enter the mixture (when it has cooled down) and provide worm castings to the mixture while they help complete the composting process.
  • Recommendations to position compost bins in full sun do not apply to many parts of Australia, as too much heat can kill off composting organisms. A shaded spot is ideal.
  • Compost bins need a cover to prevent the ingredients becoming sodden in heavy rain.

Some Composting Tips

If you are new to compost making, don’t be intimidated by statements of the ratio of carbon to nitrogen in compost making. Most recommended ingredients contain a mixture of both. With a little practice, you will quickly learn to identify and correct any imbalances.

  • Chop up tough items using shears, a shredder, or a sharp spade (spread items on soil or grass first to prevent jolting). This assists faster decomposition as bacteria work on the surfaces of organic waste. The more surfaces you can provide – the faster they can work.
  • The secret to making compost quickly to turn it regularly to keep it aerated, and to keep it damp as aerobic bacteria that commence the process require nitrogen, air and moisture to process the carbon.
  • The secret to fast composting is regular turning and mixing of the ingredients. Weekly turning while the ingredients are generating heat will produce mature compost very quickly. As the compost breaks down, the mass is reduced.
  • You don’t have to wait until you have a cubic metre of ingredients – turning and mixing ingredients will get the bacteria working.
  • If the pile looks grey or contains ants – it is too dry. Turn and mix the ingredients, while adding enough water to dampen the mixture.
  • Don’t be concerned about slaters in your compost heap. They feed on semi-decomposed organic matter.
  • If the pile is black with an unpleasant smell – it is over-wet. Air has been forced out, and anaerobic composting has begun. Turn and mix the ingredients, while dusting with agricultural lime every 15 cm, and adding some straw to the mix. Protect pile from rain.
  • If the pile seems inactive – it may need more nitrogen. Turn and mix the ingredients, while adding some manure every 20 cm. If manures are unavailable, you can substitute a generous sprinkling of poultry-based, organic-allowed fertiliser.
  • Your compost is ready when it is dark brown, crumbly, with a pleasant earthy smell and ingredients, apart from pieces of egg shell, are no longer recognisable. A 5 cm layer added to topsoil provides your garden with all the minerals that plants, animals and humans need for good health.

Compost materials

OLYMPUS DIGITAL CAMERA Compost is made by combining organic waste than provides nitrogen and/or carbon. The advice to make compost from waste that is green (provides nitrogen) and brown (provides carbon) is a bit confusing when manure contains a lot of nitrogen, but most of it is brown. When suitable dampened materials are combined in a heap that has contact with the soil, heat is generated and millions of aerobic bacteria get to work transforming the fuel into a compost-making factory.

Good Fuels

  • Manure from animals that eat grass (lots of nitrogen)
  • Chicken manure (lots of nitrogen)
  • Weeds without seed heads (nitrogen and carbon)
  • Lawn cuttings that have wilted (nitrogen and carbon)
  • Green prunings – shredded (nitrogen and carbon)
  • Raw vegetables and fruit – chopped for fast break down (nitrogen and carbon)
  • Uncooked kitchen waste – including tea bags and coffee grounds (nitrogen and carbon)
  • Old plants – chopped for fast break down (nitrogen and carbon)
  • Bedding straw for animals that eat grass or seeds (lots of nitrogen and carbon)
  • Straw and hay (lots of carbon)
  • Cardboard boxes and egg cartons – shredded (carbon)
  • Undyed wool, feathers and hair (nitrogen and carbon)

In Small Amounts

  • Newspaper and waste paper – separate sheets crumpled or roughly shredded (carbon)
  • Woody prunings – shredded (carbon)
  • Wood shavings – (very slow to break down and tie up a lot of nitrogen)
  • Seaweed – well-washed (helps factory work faster)
  • Herbs – comfrey, yarrow and chamomile (help factory work faster)
  • Egg shells – crumbled (keep compost smelling sweet and earthy)

Do Not Add

  • Plastic or foil containers, wrapping or disposable nappies
  • Fruit or vegetables that have been attacked by fruit fly or codling moth (larvae can pupate in factory)
  • Plants with diseases
  • Cat, dog or human faeces* (these can spread diseases through compost)
  • Rats or mice* (can spread diseases through compost)
  • Grey water (upsets pH balance and slows process)
  • Soil – makes compost heavy and harder to turn (amount clinging to weed roots is sufficient)
  • Earthworms – the initial heat will kill them. Earthworms know when to move into a compost factory.
  • Synthetic fertilisers (delays process and deters earthworms)

If you only have small quantities of organic waste to recycle, a worm farm would be a better solution. See Compost Worm Farm.
For information on how compost makes garden soil healthy, see Compost.
** Cat and dog faeces, and vermin, can be composted anaerobically in a small pit or container, but this compost should not be added to garden beds.

Fixing nitrogen

I get very irritated at gardening books and experts which tell Aussie gardeners that peas and beans will fix nitrogen in their garden soil. The theory being that the nodules on legume roots hold nitrogen, and when the roots die off, the nitrogen is returned to the soil for other crops. Some crop rotation patterns and recommendations for fertilising legumes are based on this myth.
Legumes roots require the presence of suitable bacteria in soil to efficiently fix nitrogen in the nodules on their roots. The legume vegetables and flowers we grow originated in the Northern Hemisphere where nitrogen-fixing Rhizobia bacteria occur in soils, but they are not naturally found in Aussie soils; they must be introduced by sowing seed that has been inoculated with a suitable rhizobium. Some groups of rhizobia are effective for several legumes; others are specific to a particular crop. Some crops, such as French beans, require a specific rhizobium that is very difficult to find here, and these will not be able to fix nitrogen effectively.
You can verify nitrogen fixation yourself by gently digging down beside a legume plant to expose some of the roots with nodules. The nitrogen-fixing nodules can be clearly seen on the White Clover roots in the photo below.

Nnodules1.jpg
Split one of the nodules in half with a thumbnail. If the interior colour is deep pink to dark red, your legumes are efficiently fixing nitrogen and a suitable rhizobium is present in that garden bed. If the interior colour is pale pink, your plants are trying hard, but there is little of the appropriate rhizobium available. If the interior of the nodule is white, your legumes are not fixing nitrogen. (See the close up of the split nodule, below.)

Nnodscut.jpg
When sowing uninoculated legume seed, you will have to include enough nitrogen in the fertiliser for good growth, and avoid lower leaves of legumes becoming yellow. This occurs when the plant contains insufficient nitrogen or magnesium and the plant draws these elements from the lower leaves to the young tips in an effort to keep growing.