A beginning vermicomposter with a finished batch of worm compost is like the dog who finally catches up to the car it’s been chasing. They both ask themselves “now what the heck do I do with this?” While producing a lively, microbially active bin chock full of wigglers is a source of pride, this success is met with new challenge: how best to harvest the castings?
Unless you’re wealthy, lucky, or sophisticated enough to be blessed with a flow-through reactor designed to make harvesting a breeze (or you’ve sprung for Worm Inn Mega) you’re going to need a way to periodically remove your castings from your worm bin that doesn’t break the bank (or your back).
Now there’s a general rule when hiring contractors that when it comes to speed, quality, and a cheap price, you can pick two, but you’re not going to get all three. The same holds true for worm harvesters and equipment for separating castings from the worms and substrate. Large, trommel-style worm harvesters are expensive, and if you’re going to attempt to build one yourself, you need some serious engineering chops. But you’re going to separate your worms from their poop in no time. On the other end of the cost scale, the low-tech light harvesting method will still help you harvest castings or worms, but it can be painfully slow and tedious.
My mission at the Urban Worm Company is to make worm composting as simple as possible. So I’d like to offer an inexpensive solution to harvest castings and safely return as many of your worms as possible back to your bin. This Urban Worm Castings Harvester is a small-scale solution constructed almost exclusively from PVC pipe, with a little help from a threaded rod, simple hardware, and a cylindrical metal mesh office waste basket to serve as the rotating trommel.
My initial testing has produced finely screened worm castings with little distress to the worm population. And best of all, it can be built for under $50 dollars with parts and materials purchased from any large hardware store. While this particular design is not well-suited to harvesting worms, it could be adapted for that purpose with a more sophisticated trommel setup.
The concept is simple. The PVC provides the frame upon which the waste basket spins around the threaded rod which serves as the axis. The castings fall into a container (in this example a concrete mixing bin) or on to a tarp placed beneath the frame.The angle at which the waste basket rotates is easily changed by sliding the 1/2-in PVC support bar to the desired height. The more full the basket, the higher the angle you’ll need to keep the contents from falling out the open end.
The trommel may be spun by hand but I prefer to use an electric drill with a bit driver and a socket to rotate it. I would imagine there are some gear heads out there may be able to fashion an even more automated motorized rotation system.
I am really excited about this harvester’s applicability for the home composter. The castings are as finely screened as any worm castings I’ve seen thanks to the tight metal mesh of the makeshift trommel, which is probably finer than 1/4-in landscape cloth. But the benefit of highly-filtered castings comes at the cost of a limited throughput. You aren’t going to work through a cubic yard of moist vermicompost in a reasonable time. To get around this, you could find a waste basket with a larger mesh or you could fashion your own mesh cylinder using landscape cloth as seen in many home harvesters.
If you’re cramped for space and have a small-scale vermicomposting system, this may be a good solution for you. When disassembled, all parts can fit inside the trommel for easy storage and it can be reassembled in less than 5 minutes.
I am offering the plans for the Urban Worm Casting Harvester free of charge. Join the Urban Worm e-mail list to get access to them immediately. I’m psyched to hear what you think.
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