Introduction: Worm Farm

About: Just your average non engineer in beautiful New Zealand, solving my seemingly unique problems because I cant find any one else that has.

How to make a Bath Worm Farm

If you look in the hardware shops and garden centres you will see all manner of Domestic "Worm Farms" for sale, most with a collection chamber built in and designed to be kept indoors;

What they don't tell you, is you are essentially buying "another child" who will require a similar amount of time to keep it running properly.


Worms don't eat the scraps you produce directly, instead they wait for a healthy population of bacteria and fungus to "chew" it in to a smoothy style for them. These Domestic worm farms are just not big enough to run without a lot of help from you;

  • You will need to "mush" all the scraps you are putting in with water to produce a nice smoothy for the worms to enjoy. ( a slower way is to dump your indoor bucket into a 20 litre bucket with a lid, and only empty in to the farm when its full and sloppy)
  • You have to be selective about what you add - no citrus, no onions, no egg shells in particular
  • You must water daily if not every couple of days, and equally makes sure the collection container is emptied.

The Bath sized worm farm however, is big enough to be pretty much self sustaining - you just need to add scraps straight from the kitchen,( all though i tend to use the 20litre bucket method) and empty the bucket when you need the stuff..

What you will need;

  • Bath: a standard domestic bath (at least 6 foot long)
  • A stand (this can range from blocks of wood to a built stand - see photo examples of my three later)
  • Bucket: 10-20 litre
  • Shredded paper: couple of big bags (start only)
  • Pebbles: approx 25 litre bag about 20-30mm size)
  • Insect screen: approx 200mm x200mm
  • Broken bricks: half bucket
  • Roof material(sheet of iron, packing case lid...)
  • Carpet: cut to fit bath out line inner.

The picture below is my latest bath worm farm, the rolls royce of worm farms i am calling it, a light tin bath mounted on a welded tube frame(recycled from an old trampoline- guess who finally got a welder)

Step 1: Whats a Worm Farm

The parts of a Worm Farm

When first starting out with worm farms its good to think of the farm as a three level house;
1.) The Basement: (Picture 1 - yellow) Loaded with gravel this is where the water and goodies drain out of the levels above and exit to the collection container.
2.) The Middle floor Bedroom: (Picture 1- Dark Green) Who wants to sleep in basement?
3.) The Top floor Dinning Room: (Picture 1 - Lime Green- Where the food arrives.

In small domestic worm farms the different levels are defined by separate containers, where as in the bath, its just interconnecting layers.

Step 2: Construction - Step 1

Decided how you are going to elevate your bath.

You need to achieve a height and method that allows you to place a suitable bucket under the plug hole, while remaining safe as the bath can gain a bit of weight when the residents move in with all their furniture and food.
  • My first farm was elevated on wooden blocks. (photo 2a)As it was a cast bath it stayed put with out a problem, however it was so heavy i had to use scissor jacks to lift it - very delicate and potentially dangerous - a controlled fall at one stage bent a scissor jack with ease...!
  • My second farm we built for a primary school, so we built a custom pole frame cut from a fallen pine tree and bits out of a near by skip - it was a light tin bath so this kept it secure.(photo 2)
  • My third farm - the rolls, as you have seen - a custom steel tube frame.(photo 2b)
  • The play center farm, built strong parents to resist the inquisitive youngsters..(photo 2c)

Natural fall
Once you have reached your ideal height, lay a the spirit level along the inside bottom of the bath (photo3a&b) and prop up the end oppisite the plug hole so there is a natural fall to the hole.

Step 3: Basement Construction

First the basement needs to be built -

  • Place a piece of fly screen over the old plug hole (plug removed) and weight down around the side with the broken bricks
( photo 4)
  • Pour your bag of pebbles into the bath, spreading out over the base about 1-2inchs and piling a little over the plug hole(photo 5)

Step 4: The Bed Room Construction

Worm Bedroom
Fill the bath to the top with shredded paper(Photo 6). This is only required for starting the farm.(more later when it comes to harvest)
Dampen down with the hose, (Photo 7)so it sinks.  If the paper sinks more than a couple of inchs, top up and re water.

Don't use newspaper or glossy paper as its full of ink and the worms tell me they get a headache eating the stuff. (they do eventually eat out their bedding too during mid night snacks)

  • The first farm i built i used a wooden crate lid, and when that rotted out i replaced it with one i made with wood and a sheet of roofing iron, hinged at one side (Photo next to green house)
  • The roof of the second farm for the school, we made from a wooden table top.
  •  The roof for my latest farm(Picture 8b)  Roofing iron over a welded steel frame with wood inserts
  • the roof of the play centre farm ( Picture 8c)
You don't need to have any holes in the roof, provided you add regular scraps there is sufficient water in them alone to keep the farm moist. ( i add about a 20litre bucket a week)

The Food and the Workers
  • Once its all damped down - add your vege scraps on top(Photo 9)
  • Chuck in your worms -  ive just added castings from my old farm - here is and indication of how its going to be;-) (Photo 10)

Step 5: Dining Room Construction

Worms are introduced to their new bedding along with some soil from their last house.(contains worm eggs) Then you start adding the food directly on top of the bedding.

Cut out your carpet to cover the food layer to the edges of the bath - this keeps the fruit flys down.

Obtaining worms
If you are starting fresh then then you need worms. Technically i understand there are at least two types of worms in New Zealand, those that live in the humus (compost layer) and those that live deeper.

I have always used the compost worms without difficulty, trapping them by placing pieces of carpet or commercial 40 litre bags of potting mix (how i discovered this) flat in the garden for a few days to a week, then harvesting when i lift.

You can also by worms in a box from some garden stores / Hardware stores.

Food of the kind that worms like best needs to be served in the dining room on at least at a weekly basis, if not daily as we do with the vegetable scraps.

Worms dont attually directly eat the food you put in, rather they wait for the microbe population to reduce it to an appertising mush. Generally thus we dont add meat scraps of any kind and, only citrus or onions skins(really slow to break down) when we are kind enough to pre mush the food - ie using a liquadiser.

All other kinds of food are ok, just break up the large bits and maybe break open things like pumpkins or stalks...

Shower and Drinking water.
All worm farms need to be kept moist, the bigger the farm the easier that is, this one we rarely added water - relying on rain water coming through the cracks in the roof. In a more dry enviroment you will need to add a weekly shower to the list, using about a 5 litre watering can fully each week or so - you will work out your level.

Step 6: Time to Empty

Then about a  6 months to  a year later when all that yummy food has been consumed and the dining room has increased in size to almost fill the bath, its time to have a clean out.

i don't try and separate worms from castings, with a good food supply they regenerate rapidly any way.  I just remove the layer of vege scraps on top, and dig out the castings, leaving a layer about 3 inch's think over the drain pebbles to restart the farm.

At this point you don't need to add more shredded paper, pile your vege scraps straight on to the remaining layer and away it goes again.

Worm Reproduction
Well feed worms make more worms... as simple as that - you can if you look closely see little white eggs,(cocoons)hence the reason for including handfuls of worm casts in any new start.

There is plenty of information, regarding worms on the Internet - it pays to get to know your workers just like any big boss.