What is a worm farm?

A worm farm is a self-contained composting system that retains most nutrients for reuse. The worm's digestive system imparts a stable crumb structure to the worm compost, which is a nutrient/rich humus material, consisting of partially decomposed organic waste, bedding material and worm castings (manure). If properly maintained, it is an odourless system.

How do you make a worm farm?

You will need to get one or more suitable worm containers, which can be made of plastic, wood or metal, e.g. a wooden box, a plastic basin, bin, or crate.  You can buy a commercially made worm bin from your local hardware store or garden centre, use an existing container, or make your own from recycled materials. 

Commercially made worm bins may be preferable if you don’t have much room, and if you get one with a tap, you can collect the ‘vermi-liquid’ for use as a fertiliser. 

Make a worm farm from recycled ingredients. Anyone can start a worm bin. All you need are the right ingredients.

Ingredients:

  Old carpet or sack. 
  Old phone books. 
  Corrugated iron – 60 cm x 60 cm. 
  3-4 car tyres. 
  Lid (use a piece of wood with a rock on it). 
  35 Saturday newspapers (or equivalent).

Step 1: First get your worms (see 'worm farming' in the yellow pages).
Step 2: Soak the newspapers in water and stuff the sides of the tyres.
Step 3: Raise one edge of the corrugated iron base with old phone books.
Step 4: Cut out carpet to the size of the base.
Step 5: Add bedding material and worms to the bottom tyre.
Step 6: Continue stacking stuffed tyres and bedding material.

Feed regularly and keep the mixture moist to touch.

Where do you get worms from?

You will need to get worms either from someone you know who has an established worm farm, or look under “Worm Farming” in the yellow pages. The species of worm most suited for worm composting is the Tiger Worm Eisenia fetida.  For a family of 4, start your worm farm with about 1000 mature worms (450 grams).

What do worms eat?

Worms are voracious eaters. They don’t have teeth, so they like their food scraps small:

• Vegetable peels and fruit peels (except acidic fruits)
• Waste from vegetable juicers
• Soaked and ripped pizza boxes
• Coffee grounds
• Tea bags
• Paper 
• Tissues 
• Dirt 
• Leaves 
• Hair 
• Cardboard fast food packaging 
• Egg shells 
• Potato peelings 
• Apple cores 
• Pea pods 
• Wood ash

What shouldn't you feed your worms?

You shouldn't feed your worms:

• Onion and garlic 
• Spicy foods  
• Meat and dairy products
• Citrus or acidic fruit should be given in small quantities only (e.g. lemons, oranges and kiwifruit)  
• Large amounts of grass clippings. Large quantities of grass clippings can cause the worm farm to be too hot

How much do worms eat?

This depends on how many worms you have. In ideal conditions, worms can eat up to ½ their own body weight every day and can double their population every few months.

If you start your worm farms with 450 gms (about 1000) of mature worms (identify mature worms by a distinct ring-shaped swelling around their body) they will consume up to ½ a pound/225gms of food waste per day. The baby worms won't eat much and will take about 3 months to mature.

It doesn't matter if you are unable to obtain this number of worms initially – just reduce the quantity of food. If you provide ideal conditions, the worm population will steadily increase, doubling their numbers every 40 or so days.

How can you help the worms eat more?

• Mash, blend, or food process scraps.
• Maintain temperature to around 24 degrees Celsius.  
• Avoid acidic foods.

What do worm farms produce?

Worm farms produce 3 products, all of which are useful. These are: 

• Worm casts or faeces, which are high in nutrients. These can be mixed with potting mix, garden soil or used as mulch.  
• ‘Vermi-liquid’, which is the liquid that drains through into the collection bin. This is very high in nutrients and can be used as a liquid fertiliser once it has been diluted with 10 equal parts of water. Diluted vermi-liquid can be used on office plants and in the garden.
• More worms. Over time your worms will breed and outgrow the space available. You can then remove some worms and give them to other people to start their own worm farms.

For more information, have a look at the Christchurch City Council’s brochure A Guide to Worm Composting (pdf 1.63 MB).