Worm castings have long been known to be a highly fertile component of garden soil. Compared to average soil, worm poop is said to contain 5 times more nitrogen (for green leaves), 7 times more phosphorous (root development), and 11 times more potassium (general plant health). They are rich in humic acids, and improve soil structure as well.
Many organic growers buy castings, while others obtain them by operating a worm composting system (vermicomposting) in the house or heated outbuilding. The system amounts to feeding worms your kitchen scraps in an enclosed bin and harvesting their castings for the garden. Unfortunately, the castings are hard to harvest without also harvesting baby worm and worm eggs. Nor could it be called a tidy enterprise. What’s more, vermicomposting bins from mail-order sources can cost $100 or more. Don’t you hate that?
I get around these limitations by harvesting, not the castings, but what I “worm tea,” or the wet waste that results from vermicompoosting (did I spell that right?). I use this as a foliar feed, by spray bottle, and the results have been dramatic. Here’s how the system works:
Buy a 10-gallon storage tub with a lid (they cost about $6 at the big box stores). Drill a dozen or so holes in the lid and cover these with window screening held in place packaging tape or adhesive caulk (for aeration, without allowing flies in). On the tub’s bottom, drill another 12 holes closely spaced, about the diameter of a milk glass, or whatever size funnel you want to use to cover these holes, which will first be covered with screening to keep worms from getting out. (Crafty little buggers, them.)
Mount the tub on a shelf such that the drain holes are free to drain into a plastic gallon milk jug below it. Drill a hole into the lid of the jug such that the small end of the funnel will just fit into the hole, snugly. You shouldn’t have to fasten the wide end of the wide end of the funnel onto the bottom of the tub. Just fuss with the height of things so the funnel meets the tub and gallon jug just right. Use cinder blocks, bricks, expendable books: you know, whatever.
Fill the tub about ¾ full of rotting straw or leaves, hay, shredded cardboard, shredded newsprint, whatever you think will make a worm home. Wet that down until it’s fully damp, then put in 500 or so red wriggler worms (Elsenia foetida) , available from many suppliers on the Internet for about $20 plus shipping. These little babies are experts at digesting organic matter, reproducing rapidly, and adapting to temperature swings.
With the worms in place, began adding kitchen fruit and veggie scraps just under a layer of bedding, not on top. Worms like to hide. Keep the upper layer of bedding moist, dampening it every few days. Not soaking, just damp.
Within a few weeks, dark brown worm tea begins to fill the milk jug. I dilute this by about ½ cup to a gallon of water. I tried it first as a transplant solution, then as a foliar feed, and the results of the latter were dramatic. Within three days, treated beans were twice the size of the untreated. Same story for lettuce and brassicas. Every few weeks, I harvest the “tea” and let the jug fill again.
In a month or two, take half the bedding and worms out of the tub and start another worm farm. Worms don’t like to live in their own castings (hey…) and will die off if not offered a fresh home. And they don’t favor soil that isn’t rich in organic matter, so if you don’t want to start a new bin, transfer the overload to your compost or leaf pile. Anything that converts leftovers into fertilizer is our friend.