I know, exciting stuff. The ranch where I am currently interning had two, well-functioning worm bins when I came on board a few months back. So well-functioning, that it soon came time for one worm bin to be harvested for castings, and its wriggly residents separated into two separate bins. That meant a third worm bin was needed, and my boss Julie let me experiment with a new design.
But first let’s talk about some harvesting techniques. Marcos Trinidad of Audubon Yes brought up a great group of teenagers from the Los Angeles area to help us out with soil building projects on the Ranch. Some of the kids got really into the worms, and we had a consistent team of four working on the harvesting. Julie’s technique for harvesting is slightly different from ones I’d seen in the past. She instructed us to take a big handful of compost, put it in a shallow cardboard box and pick the worms out from the casting material. You toss the rescued worms into a bucket, and dump the remaining material onto a screen of 1/4 inch hardware cloth for sifting.
The fluffy, rich castings that fall through the screen get laid out on plywood sheets to dry. Once dry enough to not go anaerobic during storage, the castings are kept in a 5 gallon bucket. The chunks of food and bedding that stay on the top of the screen go back into the original bin for more processing. While painstakingly slow, the method was certainly effective. We ended up with approximately seven pounds of worms and five pounds of dried worm castings. It took me plus four somewhat enthused teenagers about six hours total to get through the whole bin. Without their help, it would have been quite the challenge.
Now for the fancy new worm bin. I built up a wooden stackable design that I found in the book Compost Tea Making. I was intrigued because I’d only ever seen plastic, store-bought stackable bins. The basic principle behind stacking bins is to ease harvesting by separating finished castings from material that is still being processed by the worms. Below is a diagram of how this snazzy new bin SHOULD work.
Each level of the bin is essentially a two foot square frame made out of 2x6s. 1/4 inch hardware cloth is secured to the bottom of each frame with roofing nails to keep the levels separate. Handles are made out of strips of 1×2 wood. A square, removeable lid was made out of 1/2 inch plywood. You could easily make this design out of repurposed wood. I was in a hurry so I bought most of the wood last minute from the lumber yard.
The bedding material we use at the Ranch is well-soaked, shredded cardboard. There is no paper recycling in town, so cardboard is a plentiful waste product. I packed the whole first level with wet cardboard and put three pounds of red wrigglers in the bin. I only gave them one pound of food at first, since I knew it would take them a little bit of time to adjust to their new environment.
The desert environment I’m living in currently is extremely dry, which is a serious concern for a worm bin. To preserve moisture in the bin, I cover the bedding with a thick, wet towel. Whenever the towel dries out, I just take it off and resoak it, keeping the bedding underneath nice and moist. I also rest the first bin level on a piece of plywood, so the hardware cloth bottom doesn’t allow too much moisture to escape. A secure plywood lid is key as well. Now having used the bin for a few weeks, I suspect this design would be better to use in a milder climate, but I’m still hopeful it will work sufficiently well here in the Owens Valley. I’m really excited to see if the new bin speeds up the harvesting process, since I certainly can’t count on having a bunch of worm-loving teenagers around next time.