Mrs. Homegrown here:
One of our commenters on the compost debate, Nick H., offered up a link to a great video about worm towers, so we thought we’d share. A worm tower is a wide (at least 50cm dia.) pipe sunk halfway into the ground, with access holes on the lower half to allow the worms to come and go. Food and bedding is dropped in the top, which is kept capped.
We happen to have worm & compost expert Nancy Klehm staying with us this weekend, and she explained to us that this particular technology makes a lot of sense for hot, dry climates (note the video comes from Australia), because it’s sunken and it allows the worms to distribute themselves in the cool soil during the day. Conversely, I can imagine this wouldn’t be such a great thing in rainy climates as it could easily flood.
Nancy told us the worm holes clog up, so you do have to remove the pipe for cleaning fairly regularly, and perhaps take that opportunity to reposition it. I imagine that’s when the casting harvest would occur, and harvest promises to be a pretty messy process.
The video speaks of using PVC pipe for the tower. PVC is cheap and easy to work with, but it’s pretty well established that it leaches toxins as it degrades, so you might want to seek out pipe in other materials. As an aside, we used to use PVC pipe in our self-irrigating pots, still still have PVC in some of them, but are phasing it out in favor of metal or bamboo pipe. Yet we still have PVC lines as part of our irrigation system. This is something you have to weigh and decide for yourself.
Once Erik dragged home a section of ceramic sewer pipe he found in the street. It lingered in our yard for years, and was finally returned to the street. Now we’re singing the pack rat’s lament (See! See what happens when you throw things away!), because it would have been perfect for this.
On first glance I’d characterize this system as a novel idea, one which is worm-friendly, and best suited to hot, dry climates. It looks convenient to set up and use, but probably not the best system to use if you’re primarily interested in the castings.
If we can find another length of sewer pipe we’ll try it out and report back.