Worm Farm




About: Just your average bloke 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.



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    18 Discussions


    5 years ago on Step 5

    And how much water do i nees to add to it per week?


    5 years ago on Step 4

    Hey just wondering how many worms do i need in one bathtub and how much juice would come out of a bathtub of worms per week..


    5 years ago on Introduction

    I have a worm farm made of 4 washtubs. In the winter I set up a bucket in a bucket and take it in the house for my coffee grounds, etc. the washtubs I empty by scattering all about the garden. Then I give them a week to burrow before turning the garden over and putting it to bed. I have been doing it for about 6 years this way now.


    9 years ago

    Hello Folks,

    I know this Instructable is 2 years old as of this writing, but I have to point out that old cast iron washware was made with as much as 88% Lead Oxide in the glaze.  There are even examples of people going through the same problems the Romans experienced by soaking foods in these tubs.

    As for what our boomer generation has experieced due to these affronts, I can't tell.  However raising worms for their ability to create soil we would then grow food plants in seems at the least, risky.

    Google seach, keywords: bathtub, Lead Glaze

    1 reply

    8 years ago

    Hey hey!! Have sourced old bath tub for the princely sum of about $30 and am collecting from Orewa next weekend.

    Now...... If only I knew someone who lives nearby who could help me set it up............. lol


    10 years ago

    what do you do for winter, we have freezing temps here, do you just close it down or ???

    3 replies

    Reply 10 years ago

    Hi, I am in the non freezing temperature part of New Zealand - so i can honestly tell you .... i guess the answer lays in what earth worms normally do in the wild in freezing temps? perhaps they hibernate? This bath farm is covered by a wooden lid ( not shown in the pictures) .... sure like to know what you find out...


    Reply 9 years ago

    I'm guessing they go deep and dig under the frost line (3 to 5 feet down) around a meter.


    Reply 9 years ago

    they probably do in nature but in a bath worm farm one doesnt  have a meter of space for them to go deep but then certainaly in the upper north island we dont get freezing temperatures so there is no concern lol


    Reply 9 years ago

    oh thats good to hear.... all though one must always remain skeptic if wiki is the only reference.

    dont know bout where you live but in Newzealand if you handle to much newspaper - ie tearing it up you end up with a smudge of black ink on your hands that is pretty hard to get off... doesnt seem all that botanic to me.. and makes every thing associated with it black...


    9 years ago

    Hi I made a worm farm out of my old bath want to know if i can put one catcher of lawn clipping in the farm but I have oxalis in the lawn  is any good or should I dump the clipping can any one help me

    1 reply

    Reply 9 years ago

    hi there,  no i wouldnt put lawn clippings on mass in a worm farm - a gentle yes but not a catcher full.

    This is because grass cuttings are a wonderful activator for a compost heap, the process by which they decompose (i guess) means they generate heat among other things - equally a big mass of grass clippings you will notice often gets slimy - air is excluded and the decomposition goes anerobic... ( with out air) both of these factors are not all that inviting to worms.

    if you were to mix those grass clippings with carbon material like leaves and food scraps in a compost heap *(recommend the rotary ones) then good compost comes ...


    9 years ago

    Tip for collecting the worms: Blend leftover salad to a fine green shake and pour it in one spot on the worm bed, than put a plate over the salad (face down) and wait until dark(10ish ), then look under the plate. The secret is the worms like the dark as opposed to the moon light, where predators lurk, plus it stays moist there longer.

    1 reply

    Reply 9 years ago

    aursome thanks.. that gives me and idea;-) love to see pics of your worm farm.


    10 years ago

    I live in Canada, where it gets to freezing temperatures in the winter (in case you hadn't heard).

    In this instance I would insulate the outside of the worm farm/ tub by putting some insulation materials around it, such as straw bales for example. You could also put a specially designed soil-warming electrical cord designed for cold frames in the bin to help keep them warm in the winter. A regular 25 watt light bulb will also keep it warm enough for the worms in the winter.

    Additionally, adding some fresh Horse manure will help keep them warm all winter. Red wigglers are actually manure worms, so horse manure is their favorite food (which is also bedding). You just have to make sure that the horses haven't been given and de-worming medicine for parasitic worms, since this will also kill your worms. Also, you have to be careful that the manure doesn't contain any Horse urine. The nitric acid in the urine will kill the worms too.

    In freezing cold temps, you DO close down the outdoor worm farm in that you no longer feed them scraps until the temps go above freezing. If you open the lid, you will expose the worms to freezing temps and this will instantly kill all of them.

    Red Wigglers are natives of warm places like California. They tolerate temperatures between 5 Celsius and 40 Celsius. When the temperature gets cold they huddle into a ball and remain dormant. If it goes below 5c they die.

    1 reply

    Reply 10 years ago

    wow thanks - always good to get a different prospective... here in New Zealand's north island we don't have that problem at all and can happily keep the guys feed and watered all year around...