Worm farms

Worm farming is an easy way to compost kitchen waste. You can keep a worm farm inside in a garage or spare room or outside in the shade. Worm farms are particularly suitable for people living in units, small residential lots and small families.

You can buy worm farms from large hardware or gardening stores. Alternatively, you can make your own from two polystyrene boxes. One worm farm can consume the kitchen waste created by a two or three person household.

Make your own worm farm

Materials

You will need:

  • two polystyrene boxes, such as broccoli boxes (one should have a lid)
  • a piece of fly screen to fit in the bottom of the box
  • a piece of hose or tubing about five centimetres long.

Method

Take one box. Using a screwdriver or pen, make air holes in the lid for airflow and holes in the bottom of the box for drainage. Make sure your holes are evenly spaced.

Spread the insect screen in the bottom of the box over the holes. This will stop the worms from falling through into the tray below.

Take the second box. Cut it in half horizontally with a sharp knife so that the top box (where the worms will live) fits on top of the box just cut in half. This smaller box will act as the liquid collection tray for the worm tea that will generate in your worm farm.

Make a hole at one end of the smaller box. Insert the hose or tube in the hole for drainage.

Place the worm farm on bricks or wooden blocks in a cool, shady location. Place a container below the hose outlet to collect the worm juice.

Setting up a worm farm

  1. Begin by lining the top tray with a few sheets of damp newspaper or cardboard. This will prevent worms from falling through the holes into the drainage tray.
  2. Place a five centimetre layer of 'bedding' material on top of the newspaper. If purchasing a new worm farm this will come with a block of coir peat (coconut fibre) that requires soaking. Other bedding materials you can use include shredded paper, leaves or mulch. These should be dampened before use.
  3. Start with a minimum of 1000 worms or at least three or four decent sized handfuls. Worms breed very quickly and double their population every three months. Don’t be afraid to give worms away to other new worm farmers. You can purchase compost worms online. Do not place earthworms from your garden into your worm farm. Compost worms are a particular type of worm that breed very quickly. They can consume large amounts of fruit and veggie scraps.
  4. Place your worm farm in a cool, shaded area as worms don’t like heat. Even a little sun can cook them. Worms enjoy a dark and moist environment. Keep a layer of damp newspaper, hessian or carpet on top of the food waste to encourage the worms to come to the surface to feed. They will eventually eat this layer, so replace it as necessary.

​​Worm tea

The liquid that accumulates in the bottom tray is ‘worm juice’ or ‘worm tea’. You can use this liquid to replace the fertilisers you would normally use on your garden. You must dilute the liquid until it is the colour of weak tea (approximately 1:10 ratio). Use this to feed your plants every two to four weeks.

Feeding your worms

Feed your worms in the top tray, underneath the layer of newspaper. You can feed your worms every day or even once a week. Worms will eat approximately half their body weight in food per day. A standard-sized worm farm will cater for approximately two to three people’s food scraps.

If you produce a lot of food waste, you may have to use a compost bin to take care of the rest.

Compost worms eat almost all nitrogen-rich materials you would add to a compost heap. However, there are some ingredients you should avoid in a worm farm including:

  • citrus products such as orange and mandarin peels
  • onions
  • chilli and garlic
  • dog and cat manure.

The smaller the food scraps are when you add them, the faster the worms will get through them.

 If you are going away on holidays, the worm farm will be fine to leave for up to two months. You can fill an entire tray with harder vegetables such as:

  • celery
  • pumpkin
  • carrots
  • broccoli stems.

Harvesting the castings

As the worms consume the food in the main tray, they produce castings that resemble dark soil.

When the main tray is full of castings, it’s time to add another feed tray to your worm farm. Fill the new tray with worm food and add a new layer of damp newspaper on top. The worms will move up to the new tray when there is no food left in the first tray. This may take several months. Once the worms have migrated to the new tray, you can harvest your castings. They will be full of rich nutrients for your garden.

If you have a home-made worm farm, expose the castings to the sun. The worms will burrow away from the sunlight. You can then scrap the top layer of castings off for use. Repeat this process as necessary.

Using your finished compost and castings

Your compost and castings are ready to use when they are a rich, dark colour and resemble soil.

You can use these in a variety of ways, including:

  • using an equal amount of compost/castings to garden soil to make potting mix
  • digging the compost/castings into the top 10-15 centimetres of soil in your garden beds before planting
  • digging the compost/castings into your established garden beds, taking care to keep it away from plant stems
  • using it as a top dressing for your lawn.

Solving worm farm problems

Table about solving worm farm problems.
Problem Cause Solution
Smelly Too much food
Not enough worms
Not enough oxygen
Too acidic
Reduce food
Add worms
Aerate by stirring
Add dolomite or garden lime
Slow to break down Food pieces too big
Too much food
Cold weather
Cut food into smaller pieces
Reduce food
Feed less during cold weather
Other creatures in worm farm It is normal for small insects or other creatures to attract to the food. Some animals can help with the decomposition, others may harm the worms. Place feet of worm farm in bowls of water, or wipe Vaseline on the legs (ants)
Stir food scraps into castings
Add extra water
Vinegar flies around worm farm Too much food
Exposed food
Reduce food
Stir food through
Worms are dying Too wet
Too dry
Not enough food
Add shredded paper
Add water, place in shade
Feed more often

More information

For more information, attend one of Council's free compost and worm farm workshops.

Last updated:3 May 2019