How To

Build a Worm Farm

Worm Farming

HOW To Build a Worm Farm Guide

Why worm farm?

Save $$$$$
Around 45% of an average rubbish bag is filled with organic matter that could be composted or worm farmed.  Why pay to dump it?

Help the Environment
Organic matter thrown into landfills gets broken down by bacteria and produces methane & carbon dioxide, gases we don't want in the atmosphere.  There are 1000 landfills in NZ , which have impacts on the environment.

It's fun & easy
Anyone can make a worm bin and maintain it.  Worm farms don't smell,  don't take up much room and kids love them!

Free Fertilizer
Why pay for organic fertiliser when you can make it yourself for free.  Watch your plants bloom and grow!

Vermiculture or worm farming

Worms break down and eat a lot of organic matter and excrete it as casts (vermicasts, or poos).  The casts are richer than many fertilisers and are more natural (the casts contain 5 times more nitrogen, 7 times more phosphorous and 12 times more potassium than the soil).  It is best to place your worm bin (or worm farm) in a shady spot.  This could be in the garden, on the porch, garage or deck.   Worms prefer 18-23 °C, although they can tolerate 10-30°C.

What do I feed them?

Worms eat most things, as long as the food is damp and small enough. Worms do not have teeth but a muscular mouth and oesophagus which pushes the food down into the gut.  Glands inside the worm excrete calcium carbonate onto the food to break it down.

Worms can eat most organic matter but some things should be avoided:

Tea bags

Coffee grinds

Paper (not too much coloured ink)
Vacuum cleaner dust
Dried leaves
Small amounts of grass clippings
Small amounts of citrus
Egg cartons
Egg shells
If adding carpet, make sure it is washed off first, so no detergents enter the bin
Food scraps



Spicy foods

Garlic / Onion
Pine needles
Sawdust (it may be treated)
Bread (only small amounts should go in)
Large amounts of citrus

Worm Bio

Worms are hermaphrodites (both sexes on the same worm) but require another worm to mate with.  They lay eggs in a cocoon which hatches into the soil in 3 weeks.  Each capsule contains 3-5 baby worms (sometimes more).
Respiration occurs through the moist membrane (skin) which is another reason why the environment for the worm should be damp.


  • There are around 200 species of worm in NZ.  However, only about 10 species are valuable to agriculture.
  • Worms mature in 60-90 days.
  • Worms can live up to 15 years.
  • Worms mate every 7-10 days.
  • A mature worm can produce over 1,200 young each year.
  • Worms ingest and excrete their weight once a day.
  • Worms have 5 contractile hearts.

Which worms & how many?

Tiger worms or red worms are best for a worm farm.  They live at different depths and eat different things to earth worms.

  • 1kg of worms is around 4,000 worms.
  • 20,000 worms can digest food created by a family of 4.
  • 10,000 worms will eat around 20 kilos of food producing 12 kilos of vermicasts.
  • A kilo of worms can eat through 500g of organic waste every 24hrs.


When preparing your worm farm or bin, leave the bottom bin empty for the worm wees to collect in.  Add layer of bedding to the top bin.  Bedding may be composed of a mixture of compost, soil, potting mix, hay, a small amount of grass clippings, paper and cardboard and food scraps.  The bedding needs to be porous, loose, damp, and partially broken down before the worms are added.  As with composting, some air is needed to enter the bin.
Occasionally you may need to add some lime to the bin to keep the pH neutral.  A small handful every month should be ample (try not to get it on the worms).
There are several worm bins on the market.  Can O' Worms is a really good system, but you could also make your own worm farm out of an old bath.


After several months, the contents of the bin break down, turn brown and soil like, and castings are produced.
There are different methods of removing the casts/ compost depending on the bin.  With Can O' Worms, add a new bin with food, and the worms will migrate, allowing you to remove and use the bin with the casts.  With other types of worm farms, you may have to remove the compost layers by hand and add new matter.
When the worms have become too numerous for the bin they may be added to the garden.  This should be done in the early morning when it is cool.  The worms do not like light and will burrow down to avoid it.  Add a layer of compost after they have buried down.
Liquid may be extracted from the bins.  When using it in the garden or on plants it will need to be diluted, 10:1 (i.e 10 litres of water to 1 litre of worm wees).

Trouble shooting

Smelly worm bin? Over feeding, not balanced. Try reducing food and keeping a balance by adding more paper (carbon stuff) than food scraps (nitrogen).
Vinegar flies?
 They are after citrus and fruit. Cover the bin and add a handful of lime.
 These are a natural part of the process and help break down food.
Tiny white worms?
 These are called entrachyadids and indicate acidic conditions. Lime again!
Too many worms?
  Sell them!

Where do I get worms from?

Kiwi earthworm   
Xtreme Waste     

Where do I get bins from?

At the Environment Centre Hamilton, 25 Ward St Can O' Worms $120

At the Warehouse

Homemade from Xtreme Waste

Whaingaroa Environment Centre - Bow St. Raglan

More Info?

Contact Xtreme Waste 07 825 6509 or Environment Centre in Raglan 825 0480 or in Hamilton 839 4452


Worms galore!