Urban Bush Carpenters, I organised a worm farm seat to be made at our recent Permaculture Design Course by our *wonderful* Course Coordinator, Blake Harder. 
The key functions of this particular worm farm are to process food scraps from the kitchen – providing worm castings and worm wee for the kitchen garden nearby. It’s also central to the social area that’s integrated into the same area, providing a big comfy seat for a few people to hang out on.
In case you don’t know about compost worms yet, they’re highly beneficial for the soil and food crops – you can read about them here. In short, they’re awesome and you want them.
Blake built it out of an old bathtub and timber, only the screws and hinges were bought from the local hardware. We didn’t quite manage to take step-by-step photos of the process as we were all a bit busy (sorry), however here are some of Blake’s sketches and photos of the students filling it up and getting it operational… 
The lid detail
Crucial to a good worm farm is drainage. Blake made a false floor out of lattice and shade cloth which is cut to the right size that it can wedge into the bathtub nicely, leaving a gap that’s approximately 10cm deep, plenty of room for the worm wee to travel through the plug hole and letting in good air to the system.
James and Blake showcasing the false floor which is cut to just the right size so it wedges into the bath tub, approximately 10cm from the bottom.
The next step is to fill the worm farm with a range of organic matter. I’ve seen worm farms with only cow poo/horse poo, so it’s not essential to have diverse ingredients, but I prefer diversity at every opportunity. With this in mind, we filled the worm farm with leaf litter, some half composted organic matter, mixed greens from the kitchen and water. 
We emptied the compost worms into the top of the bath and quickly covered them as they hate sunlight. So quickly, I didn’t get a chance to get their photo. Bummer. To help moderate the moisture and temperature levels, we put a simple layer of damp cardboard on top. You could also use newspaper, hessian or thick pads of straw. I generally recommend against using carpet as most modern carpet has heavy glues in it which will harm the worms. 
Directly below the bathtub’s plug hole sits a bucket to collect the “worm wee” which can then be diluted and placed on the garden. You could build your worm farm slightly higher so you can have a large bucket beneath it, or find a bucket with a bigger capacity (and is still short) – whatever works for you. 
Some nifty handles made from old rope. Easy!
Alice and Ashlee, just acting casual
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How is it the worm farm/bath/seat going?
I’m a member of a community garden here in Melbourne and we have a spare old cast iron bathtub and I suggested this and someone said the heat we get here would kill the worms. I was after your opinion on that?
I would have thought that all the soil and the cover would insulate well enough to keep the temperature moderated.
Thanks,
Matt
Hi Matt, You’ll need to be mindful of the heat with any small worm farm – the commercial ones are the hardest as they’re tiny compared to a bath version. I’ve made plenty of bathtub worm farms over the years including in Melbourne. You just need to place them in a good spot (out of the hot, western sun), keep the water up to them and during heatwaves put ice blocks inside (on top of the layers), cover them in thick woolen blankets with the bottom in a bucket of water so it can wick over the farm. Hope that helps!
Thanks heaps for sharing. We’ve got a little worm farm going nuts, and a lovely big bath tub to expand into,but have been toying with designs, so its great to have these photos and the design to ponder… 🙂
This looks great! I’m keen to create something similar using old pallet wood. Just wondering, did you have to angle the bath in order to get the drainage through the tap right? Do you turn the tap on/off as you need it or does it free flow into a bucket?
All baths have a slight slope built into their design, so you don’t have to tilt it. We just let it free drain into a bucket and empty it as needed :-).
Hi, I love this! How do you harvest your worm castings from the tub?
Once one side of the worm farm is full of food, we let it rest to give the worms time to eat everything. In the mean time we’ll gradually add food to the other side of the bath. The worms will move over to that side once they’ve finished eating tho other side. Then we dig it out the mature castings (looks like brown soil) onto a tarp, there aren’t many worms left in the mature side (as there’s no fresh food for them). So we just wait for any left to wriggle into the centre of the pile away from the sun (which they hate) and harvest the outside layers of the pile. Eventually you can just pop a handful of worms back into the famr and put the rest on your garden.
Hi, I have made a worm farm out of a bathtub by following your design above – thank you! It is going well but the ants have found it and are crawling all over it. I have tried drenching it in water but they just return. Are they a problem or do I just live with them?
IT might be that there’s too much food waste in there and too small a worm population that can’t keep up with the food. This can happen sometimes with new worm farms. So less food waste, good moisture – but you can also smear vaseline and/or lavender around the legs of the worm farm to stop them from crawling up. Good luck!