Worm towers or worm tubes are an intriguing idea for turning food waste to worm castings. Unlike worm composting, which requires the worms, bedding, and food to be placed in some enclosure only to require you to harvest the castings, the worm tower is a “permaculture” innovation designed to allow you to recycle food waste and create worm castings without ever leaving your garden.
Most variations involve a PVC pipe buried about 12-18 inches, with holes drilled in the below-grade portion, allowing worms to go and come as they wish, much like an Amsterdam hostel, minus the patchouli smell.
At first blush, it is a fascinating concept and probably attractive to gardeners like my wife, who don’t care to handle worms. Just toss in your food waste, the theory goes, and watch the garden take off.
Excited by videos like this, I was initially very excited about worm towers, even to the point of researching the costs of manufacturing them with recycled plastics.
But after asking a Philadelphia-area composting and horticulture expert about it and getting a little tough-love and mocking in return, I’m convinced this idea has serious flaws.
The case is straightforward.
Red Wigglers and European Nightcrawlers, the two most prevalent compost worms in temperate climates, aren’t burrowers. Both of these worms live near the surface in loosely packed material like leaves.
In other words, these are the oddball worms that don’t like dirt. So you can’t expect them to eat your food waste, leave the worm tower (or tube), do their business next to the heirloom tomatoes and return to hit the buffet again.
And the larger Canadian and African Nightcrawlers that do like to burrow in soil don’t swarm food in the manner necessary to process any significant amount of it.
This is a problem because a PVC pipe stuffed with food waste will not turn into black gold.
It will turn into a PVC pipe filled with rotting food. And in the process, it will heat up, attract pests, stink to high hell, and may earn you a picketing from the local chapter of the Composting Worm Union for horrible work conditions.
The best stocking density for vermicomposting worms to process food is approximately 1 lb per square foot of surface area. This number is independent of depth; a 5-square-foot bin will accommodate roughly the same number of worms whether it is 24 inches tall or 10 feet tall.
The largest PVC pipe available to laypersons like you and me is 4 inches in diameter, the size of the largest waste lines leaving standard residential homes. It is also the size featured on almost all YouTube videos touting the worm tower.
So let’s do the math. A 4-in diameter pipe will get you a whopping 12 square inches or about a twelfth of a square foot. At 2 lbs of Red Wigglers or Euros per square foot, this worm tower will accommodate a sixth of a pound or 2 2/3 oz. of worms.
Assuming worms can eat 50% of their weight daily (and this number may be very inflated), this means our lovely PVC worm buffet will process a whopping 1oz of food each day, assuming ideal conditions. And a worm tower in the hot sun or pouring rain will not be enjoying ideal conditions.
(Update: 2lbs per square foot is far too dense for the beginning vermicomposter.)
So if you are planning to use worm towers to feed your worms in situ, you will have to accept one of two things: you will process very little waste, or your garden or yard will look like a graveyard with cylindrical headstones.
A marginally better idea is a 3- or 5-gallon bucket, which will net you around ¾ of a square foot of surface area. I did this with a little success, hosting some Euros in my garden, but still not vermicomposting food waste with any efficiency.
Yes, PVC is used commonly below the ground in all sorts of residential and industrial applications. But PVC, also known by the less benign-sounding polyvinyl chloride, was never meant to have anything but its waxy exterior exposed to soil. And by cutting the bottom and drilling dozens of holes in its sides, people are exposing the soil in their gardens to vinyl chloride, labelled a Group A human carcinogen by the EPA.
I am always impressed by the ingenuity of those leading the “permaculture” movement. I constantly see innovations that require forethought, creativity, and a willingness to be different. But like New Coke and Clairol Touch of Yogurt Shampoo (yes, it existed), some new ideas aren’t destined to succeed, some for reasons of insufficient consumer education and marketing. Others because of simple math.
I believe my former vermicomposting and permaculture muse, the worm tower, is a well-intentioned, but misguided idea because of the latter.
Agree? Disagree? I look forward to your comments and personal experience.