Worm Composting

‘Vermes’ is Latin for worms, therefore, vermicomposting is the processing of organic materials through specific types of worms to produce a high quality soil conditioner. In other words, composting with worms. It is an on-site recycling system, taking food waste and making it into plant food, which in turn feeds the plant to produce more food!

The Process

Worms don’t actually eat the food waste, as such, but they thrive on the micro-organisms that grow on the decaying organic material.

All earthworms have a grinding gizzard that processes material into fine particles. During this process, important plant nutrients like phosphorous, potassium and calcium are converted through microbial action into forms that are more soluble and available to plants.

Some species of earthworm can consume organic residues very quickly, and these are the red worm (Lumbricus rubellus) and the tiger worm, (Eisenia fetida). The red and tiger worms suitable for vermicomposting work best at temperatures between 15 and 25 degrees C, with a moisture content of between 70% and 90%.  These worms generally don’t survive in the relatively cold South Island soil, but will live happily in a suitable insulated container. Worms will adjust their populations according to available resources of food, air, water and space.

Worm composting in an enclosed container simply copies what happens in nature, with you providing the food, air and water in the right ratios to keep the worms happy.

You can feed all kitchen scraps to the worms, as well as hand towels, tissues and food-contaminated papers. Some advantages of worm composting are that it is easy to do, can be done inside or out, takes little space and is educational and fun for children!

Environmental Benefits of Vermicomposting

  • Turns organic wastes into a finely divided plant growth media with excellent porosity, aeration and water holding capacity.
  • The ‘castings’ produced by worms contain nitrogen, phosphorous and calcium in a form that is readily acceptable by plants for uptake.  Worm castings, compared to same volume  of typical soil, has 5 times the nitrate; 7 times the phosphorous; 3 times the exchangeable magnesium; 11 times the potash and 1.5 times the calcium.

About worms

Worms are, simply put, a very efficient digesting tube, made of 90-150 segments. There are about 200 different types of worms in New Zealand, with about 2,700 species internationally, who all live in different habitats.

Earthworker worms live deep in the soil, creating tunnels for air, water and plant roots, and bringing subsoils closer to the surface where they mix it with the topsoil. All worms live where there is food, moisture, air and a temperature suitable to the species. If conditions aren’t right, worms can travel up to 2kms in search of a better home.

Worms can grow a new tail, but not a new head! They have no arms, legs or eyes, but they are very sensitive to light through cells in their skin. If an earthworm is left in the light, it will become paralysed after about 1 hour.

Worms breathe through their skin, and will leave their tunnels when it rains hard because the burrows fill up with water and drown them. They have bristles around their bodies and special muscles to push them through the soil. They also excrete mucous, which not only stops the walls of the burrows (tunnels) from collapsing, but also serves to encapsulate the castings (or worm poos), making them into a slow release fertiliser.

Worms are hermaphrodites – containing both male and female organs. They mate by joining their clitella (or saddle, the swollen area near the head of a mature worm) and exchanging sperm. Each worm will then form an egg capsule in its clitellum, which can contain from 1 to 20 worms, depending on the species. The capsules, or cocoons, start out pale yellow and turn to reddish brown when they are nearly ready to hatch. An adult worm can produce an egg capsule every 7-10 days, taking 21 days to hatch, with the worms becoming reproductively active from 60 to 90 days old onwards. Research doesn’t show how long worms can live for, - appears to be anywhere from 1 year to 10!

Did you know: It was a New Zealander who showed that the weight of earthworms found under pasture was similar to the weight of the animals grazing above the ground?

How to make a happy house for worms

Worms are living creatures with their own needs. It is important to create and maintain a healthy environment for them to live and work in. If you supply the right ingredients for a happy home, the worms will respond by making you the best compost possible.

  • Choose a container, - a wooden box, dresser drawer, or commercial bins available from hardware stores.
  • Make sure the bin is aerated – with plenty of holes to allow air in.
  • Make a ‘bed’ for the worms, out of moist, shredded newspaper and a handful of soil.
  • Add worms. Start with at least 500 grams for a family of four. Contact the Council to find out where to get them. The population will grow according to the amount of food available.
  • Feed regularly. Bury the food or make sure you have a moist sacking, carpet piece or similar cover to reduce vinegar flies.
  • It usually takes at least 3 months to fill, and the worms work on the waste all the time.
  • Keep the cover moist, and it will also help keep the bin dark for the worms.
  • Harvest the vermicast when the bin is full, and use the same worms to start the process again.

Hints to help

  • The larger the surface area of food, the more quickly it will decompose. Chop or 'whiz' food if you like
  • Before harvesting your compost, stop feeding worms for a week or two, then add an onion mesh bag or similar with food scraps in it to one corner of your compost. The worms will quickly move to where the food is. Remove bag with worms and put in a covered bucket (keep dark) while you deal with the vermicompost.
  • Tip the bin out onto a big sheet of plastic or onto a concrete floor. The worms will go down away from the light. Carefully remove top layers of compost. Return worms from bucket and plastic to worm farm and start again.
  • Use all food waste, including egg shells – these provide much needed grist for the gizzard.
  • Keep the bin moist but not wet, warm but not hot, fed but not overfed!


  • Unpleasant smell: A correctly functioning worm bin should not smell. Increase the air holes, and gently stir the contents of your bin to introduce air. Stop adding food until most of what is available has been eaten.
  • Too wet: Check that the drainage holes do not become blocked. Add shredded paper to absorb moisture. Make sure that there is plenty of air circulating the bin.
  • Fruit flies: These are more of a nuisance than anything. Discourage by burying the food in the bin, or ensure that you have a good, weighty cover of wet carpet or similar. Do not overload bin.