Building a worm bin

The first step in vermicomposting is the worm bin. You can buy a commercial unit — there are several available — or build your own. The commercial units always cost upwards of $100, while the materials for building your own are closer to $10 (it really depends on what you already have on hand, or can get from a friend or neighbour). We decided to build our own.

There are a lot of worm bin plans out there, and trying to decide on one was a pretty frustrating exercise. In the end, we went with a pastiche from different sources. Our bin has a horizontal design, halved by a mesh screen. Only one half is in use at a time. I’ll explain more below. Here’s how we made our bin:

  1. Find the perfect plastic bin.

    This was a lot harder than I thought it would be. We went to Home Depot, Target, Kmart, then finally Lowe’s. The search was so grueling, in fact, that at Target, my blood sugar tanked and I knew I couldn’t keep going without an emergency calorie infusion. The secret was that we should’ve gone to Lowe’s first, because it had not just one, but several perfect plastic bins.

    The problem was that the bin needs the following features:

    • Opaque: Worms work in darkness.
    • Shallow: Worms work in the top 6-8 inches of soil. Appelhof suggests that the bin be no deeper than 8-12 inches.
    • Large surface area: Appelhof recommends one sq ft of surface per lb of garbage per week.

    None of the features by themselves were hard to find, but finding them all together was tough (until we got to Lowe’s, anyway).

    Worm bins can be made out of other materials too: wood is popular, and I even saw fabric. Plastic is popular because it’s cheap, readily available, and you don’t have to actually put it together yourself. Its downside is lack of aeration; plastic bins tend to get soggy. Soggy means water is where air should be, and without oxygen you’ll get smelly anaerobic reactions and (probably) worms who can’t breathe. That’s the why the next step is …

  2. Drill holes into the sides. The more the better.

    Not everybody has a power drill or a workshop, but we went to Hide’s lab, so it worked out.

    We used drill bits smaller than ¼″: small enough so the worms wouldn’t try to escape out of them, but big enough that we wouldn’t have to drill a million of them. When Hide asked me how many holes he should be going for, I told him, ‘As many as you can stand.’ From what I understand of composting, aeration is always the #1 consideration.

    Our plastic bin isn’t that strong, so it broke a few times when we weren’t careful with the drilling. So far it’s okay, but I’m already planning the next bin.

    I also saw another way of aerating plastic bins: louvered vents.

  3. Drill a drain hole.

    Worm bin - drainage hole with pantyhose covering it on the outside

    The drain hole is for the leachate that will probably form in a plastic bin. You want it to drain because otherwise we have that soggy, no aeration problem again. Also, the leachate is sometimes referred to as ‘worm tea’ or ‘compost tea’, but some people think it’s different and not as high quality. In either case, it can be used as a fertilizer; just dilute some in water and water your plants with it. It’s not as strong as commercial fertilizer and won’t ‘burn’ your plants. I’m pretty excited about it, but I haven’t seen any from our bin yet.

    We used the largest drill bit in the lab, about ½″, and put the drain hole in a bottom corner of the bin. Because it’s a drain hole, make sure that the hole is into the bottom of the bin, not the side. We learned about that the hard way, when we tested it out and found that the water we poured in simply collected around the drain hole but didn’t actually leave it.

    We also covered the outside of the drain hole with a bit of pantyhose, as a filter (for stuff going out) and a screen (for stuff, like small insects, going in). Bentley’s Bait-O-Matic 6000 gave us the idea for using pantyhose. When we set it up, we tilted the bin so that the corner with the drain hole is the lowest point.

    Other options for drainage include spigots, drainage lines, and the like. We are not that fancy.

  4. Install wire mesh, dividing bin in half.

    Worm bin - top view

    This is how I decided to deal with the problem of worm separation. That is, what do you do when your worm compost is finished? How do you start the next batch? There are lots of answers: you can go with a vertical system, where bins are stacked on top of each other, and fresh food is placed in a higher tray to encourage the worms to leave the lower tray. You can go with a manual sorting method: dump the contents of the finished bin onto tarp, turn on a bright light, and get to work picking out worms. There are more, and Appelhof goes over several in her book.

    I decided to go with a horizontal system, where the bin is divided in half by wire mesh. Theoretically, when one half of the bin is finished, we’ll start putting fresh food and bedding in the other half, and the worms will migrate across the mesh into the fresh bedding. Theoretically. We’ll see how well it actually works in a couple of months.

    We bought some ½″ wire mesh in the fencing section. It was more expensive than the bin, so I recommend picking up somebody else’s left over chicken wire if you can. You don’t need much, only enough to span the cross-section of your bin.

    We cut the mesh to the size of our bin with wire snips. Then we affixed it to the bin by tying it with some wire. We looped the bit of wire through the mesh and a couple of adjacent air holes, then twist-tied it outside of the bin.

    Worm bin - View of twist tie

And then we were done! See, building a worm bin is as easy as 1-2-3-4. Not counting the time we spent shopping for supplies (namely, the plastic bin), it took us less than an hour to actually build the thing.

Next: getting the worm bin ready for the worms.

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One Response to Building a worm bin

  1. Pingback: Vermicomposting introduction | extra curricula

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