Best Ways to Make Compost in the Tropics

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Turn leaves and organic scraps into Nature’s soil conditioner and improve plant performance in the garden

Our modern consumer orientated society annually discards billions of tonnes of what we consider rubbish. A large percentage of this is organic in origin. Paper, cardboard, food scraps, leaves, lawn clippings and garden trimmings are just some of the many organic materials that end up in the garbage bin and ultimately in landfill.

With a little effort and some basic information, these materials can be turned into nature’s best soil improver, compost. In the tropics this task is particularly easy to do.

Composting not only reduces the amount of rubbish that must be discarded by the community, it helps reduce the need for artificial fertilisers, improves their uptake by plants and greatly enhances water-holding capacity of the garden soil.

Compost is the result of decomposition of organic material by bacteria, fungi and soil micro-flora and fauna. The end result of this decomposition, sometimes called humus, is the best possible soil conditioner.

Most gardening techniques practiced today tend to destroy the organic components of our soils. Heavy applications of artificial fertilisers, flood irrigation, constant cropping and poor cultivation of the soil are all culprits.

As soils become deficient in humus, the degradation process accelerates and soil structure and fertility are rapidly downgraded. While chemicals can replace soil nutrients, it is a quick fix only and they are quickly lost without organic materials to bind onto.

There is no limit to the amount of compost that can be used in the garden. Compost will never hurt garden plants and, if properly made, will always enhance the soil.

Compost can be made in the traditional heap, in special bins, fibreglass containers, under plastic sheets or tarpaulins or in the many commercially manufactured containers on the market.

Where traditional methods are used, the heap should be open to the soil. That is, it should not be constructed on a concrete slab unless extra procedures are carried out. By having access to the soil, the heap attracts earthworms, crickets and other insects and their associated soil micro-flora which greatly assist the composting process. Their movement through the heap also allows the circulation of extra oxygen and keeps the heap open, friable and active.

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Use both green and brown organic materials in alternate layers as well as thin layers of animal manure if available for the most efficient composting. Keep the heap damp but not wet, and sprinkle each layer with dolomite lime. Illustration: Waldo Greiner CC BY 2.0

Where a large composting heap is envisaged, it is advisable to create a ‘chimney’ of wire or mesh, which facilitates air movement, allows entry of moisture and minimises the build-up of carbon dioxide, which can make the heap acidic and slow to fully compost.

During the Wet season, compost heaps may be covered to prevent the entry of too much water. Well prepared compost is a clean material despite its origins. This is because the process generates heat as a by-product and this heat destroys many pathogenic or disease-causing organisms as well as most weed seeds.

For maximum efficiency a compost heap or bin should be built up in layers 20-30 cm thick. Each layer of organic material should be moistened thoroughly if dry and covered with a thin layer of animal manure (or an alternative activator). In the absence of manure or in addition to it, a thin layer of sugar can be added to initiate rapid decomposition of close packed materials like lawn clippings.

Each layer should be sprinkled with dolomite lime to prevent the compost from becoming too acid and also provides two chemicals vital to healthy plant growth. When completed, each layer should be covered with a thin covering of garden soil or coarse river sand if available.

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Starting a new compost heap on banana stalks. This variation is called the Ecuador composting method. Instead of a wire ‘chimney’ there is a pole in the middle which will be removed once the heap is about a metre high to provide aeration to the centre of the pile. Image: Jan Banout CC BY-SA 3.0

This layering process is repeated until the heap or bin is full. Compost heaps should never be made too large. A far better system is to have several small heaps and be able to manage them, so one is in the process of being created, another busily fermenting and the third ready for use, rather than having one large heap that is too big to handle.

Turning of compost is not required in the tropics unless the heap has become waterlogged during the wet season or heavily compacted. The anaerobic conditions that this situation creates, leads to inferior composting and a poor-quality, acid product. Turning the heap and adding a little extra lime or dolomite re-aerates the heap and once again gives rise to the correct aerobic conditions.

As stated above, the ideal home garden compost system has one heap or bin ready for use, one composting and one being filled.

What to use

Anything organic can go into a compost heap. lf using paper and cardboard, shred these materials before use and tease the material into light layers. When placed into the heap in thick, compact slabs, they decompose slowly, become waterlogged and upset the correct working of the rest of the heap. Newsprint should never be used as folded newspapers but in single pages or shredded strips and may need extra dolomite lime to hasten its decomposition.

Grass clippings, leaves and softwood prunings are the gardener’s main source of compostable material. Thick twigs and branches can be chipped up before their addition or, if this is not feasible, burnt and the ashes added to the heap. This applies particularly to bougainvillea clippings. They are slow to rot and old spikes, which never seem to totally break down. may cause nasty wounds when handling the finished compost.

Coffee grounds are also a great additive to the compost heap, when used in moderation.  They are freely available for the minor labour of collecting daily waste from your favourite coffee shop, but they are quite acidic (pH around 4.5) so use them sparingly and counter the acidity with a little extra lime or dolomite. They are a great source of slow decomposing organic material and make an excellent soil improver.

Animal material such as prawn and fish bodies, bones, and even oyster and cockleshells may be added, but they can create an obnoxious smell during primary decomposition. If the smell is no object, they do provide valuable plant foods to the compost.

An average heap or bin of compost usually takes 3-4 months to mature and reach a stage where it can be easily used. This is, of course, dependant on seasonal conditions.

Compost is ready for use when it has a soft crumbly texture and a rich, earthy smell. lt may be either dug into the soil around the plants, used to replace poor soil, or placed at the base of mature plants. ln the latter case, compost should be protected by a layer of mulch while microfauna incorporate it into the soil.

For people concerned about pollution and creating a better environment in which to live, compost and gardening not only go hand in hand, they are essential partners.

Header image: ChameleonsEye

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