About Home Composting

Why compost?
The addition of organic material to a soil opens the soil structure to allow better balance of air and water. It also increases its retention of plant nutrients. All this encourages plants to develop a deeper, more fibrous root system which results in a more vigorous, productive, drought resistant plant. In addition, composting reduces your volume home garden output. Organic composts contain useful soil organisms which break down organic material and release essential plant nutrients such as nitrogen, phosphorous, potassium, calcium, iron, magnesium, copper, and zinc.

What materials can we use?
Organic composts are derived from such things as kitchen waste (not meats or fats), grass clippings, leaves, newspapers, hair, twigs, branches, weeds, sawdust, straw, coffee grinds, eggshells, and feathers. In other words, most organic tissue or products made from them.

Where can we compost?
Choose an out-of-sight spot with a soil that can be turned for drainage. It should be noted that working on a concrete pad or patio slab base helps prevent recontamination by soil-born plant pathogens. The space required depends on your volume of costable materials. Most people need an area of 1-3m squares (9-18 square ft.), 1-1.5m (3-5′) high. Bins of wood slatted to allow good air penetration, 4-6 stakes in the ground with chicken wire around them, or a commercial bin at least 90x90x90cm (3’x3’x’3′) are all excellent for composting.

How do I build my compost pile?
Organic material
It is important to provide a good balance of carbon (brown or dried material) and nitrogen (green material). The proportion is usually 50/50. Place layers of green then brown materials on your pile. Doing so will create compost faster and help avoid any bad odours caused by anaerobic decomposition (smell of rotten eggs). The dry brown materials compensate for the wet green materials. Your next layer should include the kitchen scraps. At this point, sprinkle small amounts of the following items in proportion to the size of your pile:

  1. One shovelful of ONE of the following: bloodmeal, raw manure, Iron Plus® 12-4-8, commercially prepared innoculant OR Ammonium Nitrate (small handful).
  2. Dolomitic lime – usually 1 handful per 1 cubic metre (3 cu. ft.) of raw compost.
  3. If you are finding your compost to be low in phosphate, add a small amount of rock phosphate or small amounts of super phosphate.

Please note that super phosphate may initially slow down composting down slightly so rock phosphate is preferable. Now cover your pile with a 3-5 cm (1-2″) layer of raw manure and then a thin layer of soil from your garden. The height of a compost pile should be 90-150cms (3-5′) as this will help generate the temperatures necessary for good composting. remember, your pile will settle, especially if it is working.

After building your compost pile, it should heat up in 1-3 days to a temperature range of 43 – 49 degrees Celsius (110-120 degrees F). After 4-6 days the temperature should be 54 degrees Celsius (130 degrees F). Higher temperatures will slow composting but most weed seeds, insects, and disease organisms will be killed. If the temperature of your compost pile begins to fall below the optimum temperatures, turn over your pile and in a couple of days it should heat again. If it does not, the composting is complete. If composting is not complete, add green materials to fuel your pile. If your compost is too dry, add water to the point that your materials are moist but not wet. To test, squeeze your compost and only very little moisture should come out. Completed compost is usually dark brown to black and has an earthy smell. It is usually clumpy and may have some uncomposted bits in it. This is normal and it may be used this way.

Compost piles must be moist but not wet. excessive moisture causes anaerobic composting which results in bad odours. Cure this by turning the pile and/or punching holes in the pile. Cover open compost piles during rainy periods to prevent anaerobic composting and the leaching away of nutrients.

After approximately 3 weeks, turn your compost pile inside out and if too dry, sprinkle water on the compost as you turn. turn again in 2 weeks. You should have some compost ready to use in 3 months. If you turn your compost every 3 days and ensure adequate moisture, you will have compost in 2-3 weeks (during mean temperatures of 20 degrees Celsius (70 degrees F).

Composting materials are usually acidic as they break down. The pH of the compost rises toward the completion of composting. Therefore, your previous light sprinkling of dolomitic limestone should be sufficient to achieve an optimum pH of 6.5 to 7.0. If your source materials were oak leaves, sawdust or kitchen scrap in large quantities, you may have to add a little more dolomitic limestone. Always test with a pH meter first before using.

If brown or dried material are in shot supply, use newspapers (cut up in strips) or dried grass clippings. Grind up all twiggy or hard to breakdown material as fine as possible. in cool periods, cover your compost to retain heat. it should be noted that excessive heat above 55 degrees (131 degrees F) slows the breakdown of your materials.

Do NOT use

  • Spruce and pine because they take too long to break down and add unwanted resins.
  • Walnut leaves and tree parts because they possess toxic Juglans.
  • Animal meat, fat and pet waste.
  • Plants that are infected with a viral disease, ie. Tobacco Mosaic.
  • Charcoal or coal ashes.
  • Plants with ripe weed seeds.

Courtesy White Rose Nursery.