How to build a compost heap
Step 1. Prepare compost area
Select a site that does not flood. Choose a shaded and well-drained area. For drainage, bare soil is better than a hard surface such as concrete.
Step 2. Gather Materials
Gather all materials together at the compost area. The exact amount of each material used varies on what is available. The basic mixture should include:
- Green plant material of all kinds (around 50 %)
- Straw or similar carbon-rich material (20 – 30 %) (some rice husks can also be mixed in but the amount used should not be too much)
- Animal manure (best mixed as liquid) (20 – 30 %).
The green material will provide carbon and nitrogen, the straw mostly carbon, while the animal manure provides nitrogen and food for bacteria.
Mixing certain types of materials or changing the proportions can make a difference in the rate of decomposition. Achieving the best mix is more an art gained through experience than an exact science.
Step 3. Piling the materials
- Make a heap in a series of layers – each layer is about 15 – 25 cm thick.
- The first layer should be with coarse and woody materials such as thin sticks or twigs. This will ensure good air circulation and drainage.
- Add a layer of more difficult to compost materials, such as rice straw, rice husks or leaves and stems of maize.
- Add the animal manure (wet) to cover the plant material.
- Add the green material that is easily composted, such as fresh grass, leaves, vegetables and fruit residues.
- Ash and urine can then be lightly sprinkled onto these layers, to accelerate the process of decomposition.
- Repeat all these layers except the first layer of coarse material, until the heap reaches a height of 1 to 1.5 m. The last layer is again green material.
Each layer should be laid down by starting at the edge of the pile so that the heap does not collapse. Care should be taken to avoid pressing the materials too much or walking on the heap while building it. If the materials are too much compacted, this will reduce the airflow in the heap and cause the composting process to develop slowly or not at all. Air vents, made out of bamboo canes with holes cut in them and placed both vertically and horizontally throughout the heap, will improve the air circulation.
Step 4. Water compost heap
Water the whole pile well until all is sufficiently moist. (See section 12 on how to check moisture.)
Step 5. Cover compost heap
The heap should be covered to protect it against evaporation and heavy rain, as this will wash away the nutrients. Use bags, grass or banana leaves for this.
Managing a compost heap
To ensure successful compost production it is important that the heap is well managed after it is built. It requires water, turning, heat and a maturation phase.
In dry conditions, the heap will need to be watered twice a week. A way of testing the moisture is by placing a small bundle of straw in the middle of the compost heap. When removed, after five minutes, it should feel damp. If it does not, water needs to be added to the heap.
There are a number of ways to reduce evaporation from the heap and therefore the amount of water that needs to be added to it:
- Cover the heap with banana leaves or grass cuttings
- Cover the heap with a layer of mud
- Do not turn the heap
If the heap becomes too wet it should be opened up and mixed with dry organic matter or allowed to dry in the sun before rebuilding.
Within three weeks of building the heap, its size will have decreased considerably. Turning the heap will replace the oxygen supply and will ensure that the material on the outside decomposes as well. To turn a heap, take it apart, mix the ingredients and rebuild it. The material on the outside of the heap is put in the middle of the heap. If the heap is dry, add water, and if it is wet, add dry matter. The first turning should be done after 2 or 3 weeks and the next after another 3 weeks.
The temperature and moisture of the heap should be tested a few days after each turning. A third turning may be necessary before all the material, other than twigs and thick stems, has decomposed.
Compost can be made without turning, but material left at the edge of the heap may not compost properly. Weed seeds and any diseased plant material present in this may not be killed. These materials should be separated from the finished compost and used in the next compost heap. Although turning is not essential it is recommended to produce better compost.
To test the heat of the heap put a large pointed stick into the heap, as shown, about 10 days after it has been built. The stick should feel slightly too hot to touch when removed after a few days. If it does not this may be because decomposition has not started. In this case, more air or water may be needed, or the heap may just need to be left for a while longer. If the heap is very hot, decomposition is happening but the excessive heat may kill the microbes. In this case, the supply of air will need to be reduced and more water added to cool it down. You should test the temperature of the heap from time to time using the stick method.
When is Compost Ready?
Compost is ready to use after 1 to 12 months, depending on the size of the materials placed in the compost system, the degree of management, and the intended use. Compost that will be used as a top dressing or mulch can be applied after the least amount of time. Compost that will be used for growing plants in the field must be composted more thoroughly.
Signs that your compost is ready to use (finished compost):
- The pile has shrunk significantly, up to one-half its original volume.
- The original organic materials that you put in are no longer recognizable for what they were.
- If you are using a hot composting method, the pile will be no longer generating a significant amount of heat.
- The compost has a dark crumbly appearance and has an earthy odour.
If your compost is not ready for its intended use, it should be “cured” for a period of time. Curing is the process of allowing compost that has completed the hot phase of composting to finish the composting process. Even at this stage the heap should be kept covered to protect it from the rain and sun. Make sure the compost is moist (but not wet!) and aerated during the curing period, which can be as short as one month or as long as a year or more. However, if the compost is stored for too long before use it will lose some nutrients and may also become a breeding place for unwanted insects.
Your composting system may not break down all the larger materials, such as corn cobs or wood chips, in the first batch of compost that you make. When you sieve your compost, any material larger than grid of your sieve can be removed (see picture). These materials are called “overs” which can go back into the compost system the next time that you build a pile. The overs provide bulk for aeration and microbes attached to these pieces will help jumpstart the new composting process.
Compost maturity tests
Most farmers don’t do any testing of their compost. After a while, you’ll get a “sense” of the look, feel, and smell of finished compost. For uses other than top-dressing or mulch, immature (unfinished) compost may stunt or kill plants. Therefore, a farmer should determine compost maturity before incorporating compost into the soil.
A simple testing method is to put your compost in a couple of pots and plant some radish seeds (or seeds of any other plant that germinates and matures quickly) in the compost. If 3/4 or more of the seeds sprout and grow into radishes, then your compost is ready to use.