How to make a large worm bin
There's so much I want to
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
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
- 16 cinderblocks (or some treated 4"X4"s) for legs
We cut one of the 2X12s and
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
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.
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.
Total 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.
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