Composting

Composting is a process in which organic material is broken down by bacteria and other soil biodiversity via decomposition. The resulting material is called compost, which is a valuable organic soil amendment, and mulch. Making your own compost is a good way to use garden and kitchen waste and is a cheap way to make organic matter for soil improvement.

What can you compost?

Compost is usually made from plant materials that are categorized into “Greens” and “Browns”.

“Greens” are materials with a lot of nitrogen and tend to be fresh and sappy. Some examples found at home and in the garden are:

• Freshly pruned leaves

• Weed-free grass clippings

• Uncooked leafy vegetable scraps

• Soft fruit peels, like from bananas and mangoes

• Tea leaves

• Coffee grounds (Do not use coffee grounds that have been roasted in oil, as the oil will turn rancid in your compost)

“Browns” are mostly made of carbon and are dry and pulpy. Some examples found at home and in the garden are:

• Dry leaves

• Twigs

• Sawdust

• Cardboard egg trays

• Paper

• Cardboard

• Woody stems and soft wood (Make sure these materials are broken down into small pieces before you add them to your compost as they take the longest to decompose)

Organic materials will break down faster if they are in smaller pieces, so it is best practice to cut up them up before adding new materials to your compost.

A good rule of thumb is to add 1:2 greens to browns to keep the compost healthy. Too many greens can result in anaerobic decomposition.This occurs when the liquid released by the greens prevents oxygen from reaching the middle of the compost, resulting in unpleasant smells and slimy material. Too many browns can result in the compost becoming too dry and slowing the decomposition process dramatically.

In the tropics, the humid and damp environment tends to cause compost to decompose anaerobically. This can be fixed by adding more browns and mixing the compost regularly. It is best to err on the side of caution and always add more browns than greens. The compost can be then watered as needed till the mixture feels damp like a wrung-out sponge.

Take note that compost can be made unusable by certain materials. Weeds, diseased plant parts, and cooked food with salt and oil will make the compost harmful instead of helpful in the garden!

What should I compost in, and where?

Composting in gardens and homes is usually be done in a container of some kind. These containers are usually made of plastic that can be drilled to make holes for aeration and still protect the compost from pests like rodents. Compost can also be made in a heap and covered with a tarp or shelter, but this is less secure from animals, generally messier, and will need a large space.

Compost should be left in a shady area out of the rain or sun to prevent it from getting too dry or wet. Dry compost will stop decomposing, while overly wet compost may start becoming anaerobic, and produce unpleasant smells.

Types of composting

There are many different ways to compost, with different methods having a variety of strengths and weaknesses. The most common methods in Singapore are:

Traditional composting

Traditional or aerobic composting is the easiest method, but also requires a large container or heap and some time. Decomposition will happen at the best rate when the compost is at least a cubic meter in volume and will take between 3-6 months to mature. Smaller amounts of compost may take longer to fully break down. If a container is used, it is important to have plenty of air holes to prevent anaerobic decomposition, which is caused by a lack of oxygen in the compost and causes bad smells.

For a new container or heap, greens and browns are mixed or layered in a 1:2 ratio. Garden soil or existing compost can also be added to introduce soil microbes and start the decomposition process.

Greens and browns are slowly added over time in a 1:2 ratio. The immature compost should be mixed with a garden hoe or spade at least once a week to keep it aerated. Over time, the older composting material will fully break down, and become mature.

Because of the mixing and continuous adding of materials, mature and immature compost will be mixed with larger materials that have not decomposed. Mature compost tends to settle at the bottom, so some gardeners will flip the entire bin or pile and dig out mature compost to use. Mature compost can also be filtered out from immature compost by using a screen. Mature compost should feel soft and fine with a pleasant, earthy smell. If the compost feels chunky and has an acidic, unpleasant smell, it is not ready for use, and can be returned to the compost.

Need a step-by-step reference on how to make traditional compost? Download our brochure on how to set up your own traditional compost bin here!

Vermicomposting

Vermicomposting is similar to traditional composting, but with the addition of composting earthworms. These worms are not the same species as the ones found naturally in gardens as they are adapted to living in mostly organic matter and not true ground itself. Composting earthworms eat the decaying organic material, producing vermicasts as they digest their food. Vermicasts are a useful organic fertiliser that can be used as a source of nitrogen for plants.

There are custom worm bins that can be bought to protect the earthworms from predators and to make the collection of vermicasts and mature compost easier. They come in various sizes and are usually much smaller than traditional composting bins. They need plenty of air holes to keep the earthworms healthy, and a drainage mechanism to remove excess liquid produced by the earthworms. This liquid is called worm leachate, and like vermicasts, can be used as organic fertiliser.

Earthworms will break down most kinds of leafy kitchen waste and fruit peels very quickly, but are sensitive to acidic materials like citrus peels, as well as strong-smelling produce like onions and garlic. They also eat pulpy brown materials like cardboard and newspapers. Unlike traditional compost, more greens can be added periodically as the worms eat these materials first.

Earthworms are sensitive to light and heat and are prone to escaping or dying if their container gets too hot. Similarly, they will escape if their compost is too wet, and die if it is too dry. Keep your vermicomposting bin in a cool, shady area out of direct sun and rain, and regularly check to see if the compost feels like a wrung-out sponge. If the material is too dry, add some water, and if it is too wet, add more browns to absorb excess moisture.

Like traditional composting, the final product should feel soft and fine, with a pleasant smell. Because the vermicasts are already mixed in the compost, the final product generally has more nutrients than traditional composting and can be used to boost plant growth.

In-ground composting (Worm towers)

In the past, people used to simply bury their composting material directly into their planting areas. However, the decomposition process tends to use up nitrogen while it is happening, resulting in plants growing near actively decomposing compost to become nutrient deficient and vulnerable to pathogens that might be in the immature compost.

Containing the compost in a pipe directly in your growing area is a more practical way to keep immature compost away from sensitive plant roots, and helps to feed your soil biodiversity.

Worm towers are pipes or pots cut in half to contain composting material above ground, encouraging earthworms that live in true ground beds to eat and bury the material throughout your growing area. Take note that these earthworms are different from the worms used in vermicomposting because they are adapted to living in proper soil with clay components, and not purely organic material.

Worm towers need very little maintenance as they don't require mixing and the compost is automatically added to your growing area, but the size of the pipe or pot does limit how much compost can be made at any one time. The pipe or pot will also need to be covered with a lid to prevent rodents from digging up unfinished compost and making a mess.

When is my compost ready for use?

Gardeners should ideally use compost that is no longer actively rotting. This is because actively rotting compost uses up nitrogen, has large chunks of food or plant waste that can attract pests. Additionally, it may have high levels of bacteria and fungi present that can cause disease. When the rate of rotting slows, the compost can be considered mature. Mature compost should feel soft and fine with a pleasant, earthy smell. If the compost feels chunky and has an acidic, unpleasant smell, it is not ready for use, and can be returned to the compost bin.