Composting Systems

There is no one best system for managing compost. Instead, there are many ways, each offering advantages and benefits. Systems can range from mulching leaves on a path to gathering a batch of organic matter for a three-week hot compost.

To determine which system is most appropriate for you, consider such factors as how much time you want to devote to composting, how much garden space is available, how much organic waste you have and how much money you want to spend.

What to Compost

Anything organic can be composted but some materials are more appropriate for composting than others. Material that would otherwise go out in your rubbish, like food waste and leaves, can go in the compost. The wider the variety of material the better. Variety increases the chances of achieving a balance of carbon and nitrogen and widens the range of elements that will be returned to the soil. How well your compost bin controls the environmental parameters of moisture, humidity, aeration and temperature determines how fast your wastes will break down.

Apples - source of phosphorous and potash (potassium).

Banana skins - source of phosphorous (P) and major potassium (K), decay quickly.

Beet wastes - source of magnesium, calcium and nitrogen

Blood meal - good nitrogen source (12 per cent); helpful to add when material to be composted is carbon-rich.

Bone meal - good nitrogen source (2-12 per cent), major phosphorous source (20-25 per cent).

Citrus waste - minor P high in K, nutrient source.

Corncobs - will take a long time to break down unless finely shredded.

Food waste - vegetables and fruit - nitrogen-rich material, decompose faster when they are chopped into smaller pieces. Dig into centre of material and cover with carbon-rich material or soil.

Grapes - stalks and leaves minor nutrient source, adds bulk promoting aeration, cut into smaller pieces.

Grass clippings - Actually, it's usually easier to leave grass clippings in the lawn, where they will decompose and benefit the soil directly. However, they can be composted, too as they are excellent source of nitrogen in compost bins but be sure to add grass clippings in very thin layers and mix them with brown materials like leaves, otherwise they tend to become slimy and matted down, excluding air from the pile. Caution: avoid use of clippings from grass treated with pesticides until after three to four cuts.

Hair - good source of nitrogen, mix with other materials. Do not use if hair has been chemically treated.

Hay - Farmers are often very happy to get rid of spoiled hay bales that have been out in the rain, and will give them away or sell them at a low price. Grass hay will probably contain a lot of seed, which unless your compost is hot enough to kill them may re-sprout in your garden. High in carbon, chop or shred and wet for faster composting. The greener the hay the more nitrogen it will contain.

Kitchen waste - Fruit and vegetable peels/rinds, tea bags, coffee grounds, eggshells, and similar materials are great stuff to compost. They tend to be high in nitrogen, and are usually quite soft and moist. As such, kitchen wastes need to be mixed in with drier/bulkier materials to allow complete air penetration.

Leaves - an excellent free source of carbon material. Collect in the autumn for use during the gardening season. Mix with nitrogen-rich material. Ash and poplar leaves can raise soil pH if used in compost -- this may not be beneficial if your soil is already alkaline.

Manures (horse, sheep, cow, chicken) -Best to compost before use as some fresh manures will burn plants. Good source of nitrogen and other nutrients (the fresher the manure, the more nitrogen it contains). Fresh manures can get a compost pile to heat up quickly, and will accelerate the decomposition of woody materials, like autumn leaves. Some manures may contain weed seeds.

Mushroom manure - excellent soil builder, low in nutrient value but could possibly contain pesticides. Check when obtaining.

Newspaper - best to recycle, contains no nutrients but shredded can serve as carbon material. Good to mix with a very wet material like grass clippings.

Sawdust, wood shavings - good carbon-rich material for composting but takes a long time to break down.

Straw - Dry straw is a good material for helping to keep a compost pile aerated, because the stems are hollow and stiff it tends to create lots of passageways for air to get into the pile. Be sure to wet the straw, as it is very slow to decompose otherwise. Many stables use straw as a bedding material for horses -- straw that has undergone this treatment is mixed in with horse manure and breaks down more quickly.

Weeds - good nutrient source. Best to use when green and no seed heads. Pernicious/perennial weeds should be dried before adding to compost. Avoid weeds that have begun to go to seed, as seeds may survive all but the hottest compost piles.

Wood ashes - excellent source of potassium. Sprinkle directly into garden soil.

Rhubarb leaves - There are at least two points of view on the composting of rhubarb leaves. One suggests not to compost rhubarb leaves because they contain chemicals, which may be toxic to organisms in the soil. The other point of view suggests that the oxalic acid released by decomposition will lower pH and inhibit microbial activity, but that as long as the rhubarb leaves are mixed with other materials and as long as not too many are added at any one time, they are an acceptable composting.

Materials NOT suitable for Composting

Barbecue ashes/coal - contain sulphur oxides, bad for garden. There is also concern with the chemicals applied to the barbecue bricks to assist ignition.

Cooked food waste - may contain fats, which will attract animals.

Couchgrass or other grasses with a rhizomatous root system - require thorough drying before adding to compost bin or they will grow again.

Dairy products (butter, cheese, mayonnaise, milk, yoghurt, sour cream).

Dishwater - most dishwashing soaps contain perfumes, greases, and sodium.

Dog, cat faeces - may contain disease organisms. Cat droppings may contain Toxoplasma gandi or Toxocara cati, a roundworm. Both can cause blindness, particularly in children.

Fats, grease, and oils - putrefy and smell bad as they break down.

Fish scraps - attract animals, fish scrap contains a lot of fish oil and breaks down more slowly.

Grains -may contain fats, which give off odour in their breakdown and attract rodents or other pests.

Cat litter - likely to contain disease organisms.

Meat, bones - attracts animals and can be very slow to break down, because the fat can exclude the air that composting microbes need to do their work.

Weeds that have gone to seed - compost unlikely to reach temperatures high enough to kill off the seed

Weeds like Convulvulus and buttercups - may live on in the compost unless they are completely dead and thoroughly dried.

Chemically treated woods -Sawdust is often available from building sites, friends, or your own building projects. If you are considering composting sawdust, be sure of the origin of the sawdust. Sawdust from chemically treated wood products or creosoted wood can be bad stuff to compost. For example, pressure-treated wood (sometimes called Tanalised which usually has a greenish tint to it) contains arsenic, a highly toxic element, as well as chromium and copper. There is evidence to suggest that arsenic is leached into the soil from these products when they are used to make compost bins or raised beds, so composting the sawdust would certainly be a mistake.

Diseased plants - Many plant disease organisms are killed by consistent hot composting, but it's difficult to make sure that every speck of the diseased material gets fully composted. It's best not to compost diseased plant material at all, to avoid re-infecting next year's garden.

Human wastes - Human faeces can contain disease organisms that will make people very sick.

Making Compost - A Summary

  1. Buy or build a rodent-resistant bin.
  2. Locate the bin on well-drained, level soil.
  3. Use coarse organic material such as straw or prunings on the bottom few inches.
  4. Chop material into smallish pieces.
  5. Add green nitrogen-rich material (moist) and brown carbon-rich material (dry).
  6. Dig food waste in the centre and cover. Aerate the material once a week.

Compost Bins to Make

The Wire Mesh Bin

The Pallet Bin

The Baffled Bin

Brick Built Bin

Using the Compost

The final stage of composting is using the finished product.

The next stage is wishing you had more of it.

Your compost should be ready for use anytime between four months and two years from when you began composting. You know you have finished compost when it is dark in colour, crumbly but not powdered and smells earthy.

These are indications that the compost has stabilised - or matured - and that the original raw organic material has been converted into nutrient-rich humus. If you wish, a simple pH test kit can give you an indication of maturity.

Compost is classified as a soil conditioner rather than a fertiliser. To be classified as a fertiliser it would have to have higher levels of nitrogen, potassium and phosphorous. Finished compost does add these elements, and others, but tends to release them over a longer period of time than chemical fertilisers.

Compost also adds organic material to the soil, increases permeability of clay soils and increases water-holding capacity of sandy soils, promotes root growth and creates spaces for air and water. Finished compost is usually found at or near the bottom and centre of the compost bin.

For many applications it is desirable to screen the compost through a one-half-inch mesh before using it. Material that doesn't fall through the screen can be thrown back into the bin for further composting or used as mulch.

The early spring is the best time to add large volumes of compost to the garden. It can be dug into the top six inches of the soil. By mixing the organic matter with the slowly warming earth, it supplies nourishment just in time for planting. Screened compost can be used with an equal volume of soil and sand for a seedling mixture. Use it straight up for a top dressing on potted plants and patio container gardens. For containers and hanging baskets use one third compost, one third potting soil and one third vermiculite or Perlite.

Ways to Use Compost

Top Dressing - Top dressing is placing compost on the soil around the bottoms of flowers, vegetables, shrubs, and trees, leaving the stem free for air to circulate. With larger trees, the compost can be placed on top of the soil six inches from the tree's trunk to just beyond the drip line. Aerate the lawn in the spring by pulling cores (machine or hand tool) then rake 5 cm of screened compost over the lawn surface.

Mulching - Mulching is similar to top-dressing. The compost or other organic material is placed on the soil to finish breaking down. (See separate feature for more details) Aside from adding organic material, mulching helps retain moisture in the soil, smothers weeds and inhibits soil compaction. Be sure to remove weeds before mulching. Grass clippings left on the lawn, as a mulch will help retain moisture and provide nutrients. Mulching has many benefits. Many gardeners mulch with organic materials to discourage weeds, to keep plant roots cool and moist, to protect plants from frost, to prevent soil erosion and compaction and to reduce the need for watering in the summer. Spread the organic material on top of the soil around plants and on garden paths.

Transplanting - Dig a hole twice the size of the root ball, mix compost with an equal part of topsoil and fill in around the root ball, tamping the mixture just enough to eliminate air pockets. Water gently.

Compost 'Tea' - Fill a cloth bag with a litre of compost. Tie the bag and soak in a garbage can full of water. Let it steep overnight and pour the "tea" into the soil for your plants. If you let the compost steep longer than overnight, the water may need to be diluted before pouring.

Common Compost Problems and Solutions

To deal with possible nitrogen shortage, add an additional source of nitrogen, such as bloodmeal. You may experience an increase in the snail and slug populations, especially if the weather is wet.




Compost pile has a bad odour

Not enough air: pile too wet

Turn it; add coarse, dry material (straw)

Pile is dry throughout

Not enough water; too much woody material

Turn it and moisten materials; add fresh wastes; cover pile

Compost pile is damp and warm in middle but nowhere else

Pile is too small

Collect more material and mix the old ingredients into a new pile

Pile is damp and sweet-smelling but still will not heat up

Lack of nitrogen

Mix in a nitrogen source like fresh grass clippings, fresh manure, bloodmeal, or ammonium sulphate

Pest infestation - dogs, rodents, insects

Improper food scraps added

Don't add meat, fats, bones or other animal wastes. Use a rodent - proof compost bin. Food scraps not covered Place fruit and vegetable wastes in the centre of the pile.

© copyright 1999, P. A. Owen

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