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How to make a large worm bin

Worm bin designThere's so much I want to tell you about our new worm project that I decided it needed to be a lunchtime series.  I'll start out with the design of our large-scale worm bin.

As you can see from this first photo (upside down during construction), the bin is pretty simple.  Our supply list included:

  • 3 @ 4'X8' sheets of plywood (for lid and two bottoms)
  • 3 @ 2"X3"X8' (for spacer between bottoms)
  • 3 @ 2"X12"X8' (for walls)
  • 3 hinges for the lid
  • 2 clasps to hold the lid shut
  • screws
  • 16 cinderblocks (or some treated 4"X4"s) for legs

Drilling holes in the bottom of the worm binWe cut one of the 2X12s and one of the 2X3s in half (and if we'd been thinking straight, would have cut three inches off the ends of the other pieces of lumber so that we wouldn't have to fill in the gaps where the bin is a little bigger than the plywood.)  Then we screwed the 2X12s together into an eight foot by four foot box and topped it off with a sheet of plywood.

This sheet of plywood will be the bottom of the worm chamber, so we drilled half inch holes every foot along the length and width for drainage and to give the worms a bit of bottom aeration.  Mark also drilled a slightly larger hole in the corner which would become the downhill end when the bin is turned over so that water wouldn't pool there.

Next, we made another box out of the 2X3s and set it on top of the plywood, then added a second sheet of plywood on top of this box.  The result is a tray under the bin to collect the compost tea.  A hole in the downhill corner allows compost tea to drip into a bucket.

Worm bin legsAfter flipping the bin over, we set it up on cinderblocks.  4X4 legs would have been cheaper if we were buying them new, but we always have a lot of seconds cinderblocks lying around, so it was easy to stack four blocks on each corner.  We were working on a bit of a hill, so we didn't have to add any extra blocks to make one end of the bin higher than the other.  The purpose of raising the bin off the ground is twofold --- to allow us to catch the compost tea and to allow for aeration under the bin to keep the bin aerobic.  The downside is that we can't use the earth's temperature to mitigate summer's heat and winter's cold, but with a large bin, worms should be able to keep working all year round anyway.

The last step is to add a lid on top.  A piece of plywood should be enough to keep animals and rain out while keeping the bin moist and dark.  No pictures of this step yet since we ran out of time on Friday and didn't install the hinges yet.

Worm bin drainageTotal cost for the worm bin, using nearly completely new materials, is just under $100.  We figure we'll probably expand into a second bin this summer, and are already thinking of ways to make the second bin better.  Would a bead of liquid nails along the edges of the bottom keep moisture from settling into the joints and rotting out the wood as fast?  (We can't use treated wood since treated wood is reputed to kill worms.)  Could we make a cheaper bin by using multiple 2X6s or 2X4s for the walls, or maybe even plywood?  I'm sure that worm bin 2.0 will be even better, but this one was easy to make and should work fine for now.



This post is part of our Hands-on Wormkeeping lunchtime series.  Read all of the entries:





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Why not paint the inside of the worm bin with a polyurethane boat lacquer? That would make it watertight and prevent rot. Polyurethane is sold as both a single or two component variety. The single component stuff cures with moisture from the air. The two component variety cures when both components are mixed. This is often used on wooden boats, because it resists moisture and light well once it's cured. It will not leach components.

Alternatively, try finding an old polyester/fiberglass bathtub for your next bin. It will be watertight and comes with a ready-made drain hole in the bottom. :-) They might even come with insulation already applied. The gelcoat that is used on the inside is harmless to human cells (we've had several kinds tested for biocompatibility at work; they were all OK) and so presumably to worms as well.

Comment by Roland_Smith Mon Feb 21 13:00:29 2011
I agree with the free or nearly free bath tubs (check local remodeling companies or town dump). Just leave the drain screen in place (or piece of SS hardware cloth) and prop it at a reasonable height for your convenience for input and output products. Barring that, I would think 1x material would be strong enough for several years, as you aren't making them really large. For the next one, not a bath tub, you may find a center brace may be advisable anyway as it's a good bit of wet weight even though it's not that large and may bow down in the center. Just take 1x stock and build a ledge to lay the plywood on with as many cross braces you want, drop the plywood into the box frame and screw the plywood to the ledge and caulk the ply to frame joint. The "tea" will still drain through your drilled holes. The bath tub seems like the easier of the two, and definitely less costly.
Comment by vester Mon Feb 21 18:10:02 2011

Roland --- I should have known you'd have a non-toxic sealing option idea! Sounds like boat lacquer is a good idea.

Roland and Vester --- I really like the bathtub idea too, but haven't been able to come up with any free ones yet. We'd probably need about four or five of them to match the area of our current bin. Our county dump has stopped letting people take away trash (!!!), which makes things difficult.

Comment by anna Mon Feb 21 21:05:51 2011
How about putting up some signs at the gate to the dump, at the local grocery store, hardware store, etc., saying you would like old bathtubs. If you offer to pick them up, you might get quite a number of them!
Comment by Sheila Mon Feb 21 23:03:20 2011
For tubs try Craig's list again and here is a link to Va. Freecycle groups to find one local to you http://www.freecycle.org/group/US/Virginia You can find almost anything on here and the only requirement is that it is free.
Comment by vester Tue Feb 22 01:43:50 2011
Sheila and Vester --- good ideas on finding bathtubs! The only one I'm not too keen on is freecycle. I love the idea, but in our local area, I eventually removed my email address from their list because of the endless sob stories people sent out. It was just too painful to read them every day. I suspect that in a less economically depressed area, freecycle might work more as envisioned rather than turning into a lot of people begging for castoffs.
Comment by anna Tue Feb 22 09:26:24 2011
This sounds like a terrible idea (coating the inside of the bin with a "moisture barrier". If it stops moisture, it'll likely stop air as well. This will kill the worms. Worm bins are supposed to be made from untreated wood. Eventually the worms will start eating the wood as well. And the sealant likely is not organic. Stay with the plain wood
Comment by Adam Mon May 14 03:31:17 2012
Adam --- We did end up sticking with plain wood, and it has worked well so far (although the bin is only a year old....)
Comment by anna Mon May 14 08:23:36 2012
I love reading about all the worm bins people craft at home. I too am trying to build one. One change that I think I will make from yours is to build the frame out of pressure treated lumber (or some other type of non-toxic treatment) in order to make the frame stand up longer. Then I will use untreated wood for the inside walls of the bin. The reason for this is to be able to replace just the walls when they rot and not the entire bin. I've seen large 5' x 8' x 2' bins online for $5,200 and know I can build one cheaper. These $5,200 ones have powder coated metal framing and wood walls. They also have the 2" x 2" metal grate on the bottom and winches to harvest. I'm not a woodworker by any means. I think I may pay a metal shop to build just the frame and grate and I will finish the job. The online ones are modular. I'm not sure if I'll be able to do that, but hope I can. I look forward to any updates you all may have. I've also read about using only cinder blocks for a bin (stacked 3 high).
Comment by Adam Wed Jul 18 03:50:52 2012

Adam --- I'm relatively sure pressure-treated lumber would kill worms, which is why we used untreated wood. I'd be leery of using it even for the frame since I'd think some of the chemicals could leech inside the bin.

I understand your concern about untreated wood breaking down, but since you can build a bin out of untreated wood for less than $100, there seems to be little point to overbuild it. Even if you built a new one every three years for the next sixty, you'd have only spent $2,000! I suspect a bin would last considerably longer than three years too --- the one shown here has been in service for a year and a half with no signs of decay yet.

We have changed our design slightly, though, to make it more ergonomic. Still playing with the lid --- we liked this design even better.

I'll be curious to see what you come up with!

Comment by anna Wed Jul 18 07:22:08 2012

Adam, the cinderblock idea sounds nice. Only downside is you can't collect the liquid from the bin. I never do this anyways though really, so this might be a great way to go.

I believe plywood is usually adhered with glues, I'm guessing toxic to humans if ingested, and certainly breaks down over time. Same thing with the construction adhesive you mentioned. I think it would be best if you could build the entire thing out of untreated lumber of some sort. And construction sites often have lots of short ends left over (less than 4 feet) and if the company is approachable, they'll probably set aside those short ends for you.

I like the idea of metal, it breaks down fairly naturally, good for the soil in small amounts, and sturdy. I wonder if one can buy plans for one of these, so that we would have something to bring to a metalworker in our community and not have to draw it ourselves (which some of us may not be so great at). That would be a nice to have access to in some way.

Comment by Anonymous Sun Sep 16 13:09:37 2012

Loved reading about your worm bin adventures! What is the name of the ebook to start your own business that is mentioned above? I followed the link but there are several books there. Thanks so much

Comment by Kimberly Sun Feb 2 20:01:15 2014
Kimberly --- You're looking for Microbusiness Independence. Thanks for your interest!
Comment by anna Mon Feb 3 16:11:56 2014