When I first got into vermicomposting with red wigglers 5 years ago, my first compost worm bin was a styrofoam cooler with about 1 square foot of surface area. It worked for a while, but my colony eventually died out. I think the primary reason was the container was just too small to allow the red wiggler worms to move to the areas that best suited them. I’ve also tried plastic compost worm bins, but I find that the plastic makes it easy for the bin to stay too wet.
For the past 4 years or so, I’ve been building my compost worm bins out of wood, and making them large enough that there’s plenty of room to bury the food scraps and for the worms to move around as needed. My preferred material now is rough-sawn hemlock, but any wood that is not chemically treated will work fine. The wood will decompose slowly, but you should get at least 5 years out of it before it rots too much to be usable as a compost worm bin (and then you can still re-use it as a flower or herb bed).
The size of compost worm bin I recommend (and offer for sale when I’m at a Farmers Market) is 38″ long X 14″ wide X 12″ deep. That provides inside dimensions of 36″ X 12″, or exactly 3 square feet. Three square feet of surface area is sufficient for 3-4 lbs of red wiggler compost worms — so if you start with 1-2 lbs, you’ve got room for the colony to expand. It’s always better to have a compost worm bin that’s a bit too large for your current needs than a bit too small. The bigger the bin is, the better it keeps at the correct moisture level and the less often you need to empty it.
There’s no need to ensure that the joints of the bin are 100% tight and worm-proof. As long as you maintain good conditions in the bin, the red wiggler worms would much prefer to stay in the moist, food-filled inside than to venture out. I also don’t use a tight-fitting lid — I usually just lay a piece of cardboard over the top of the compost worm bedding to keep moisture in and light out. I’ve never had a problem with compost worms escaping from a setup like this.
It’s practically impossible to completely worm-proof a container, anyway. Even plastic containers with snap-on lids have enough gap around the lid for the worms to escape. All but the largest red wiggler compost worms can even squeeze through standard window screen. It’s far better to concentrate on creating good living conditions for your red wigglers than to try to create a “cage” they can’t escape from.
It’s pretty easy and inexpensive to build your own bin if you’re fairly handy. I also offer them for sale sometimes — contact us for more information.
Happy worm farming!