worms

The worms are hard at work making compost for the Seattle Community Farm, thanks to some newly remodeled digs. Recently the students from the Rainier Vista Boys and Girls Club helped set up three vermicomposting bins near the Children’s Garden, tearing up newspaper for bedding, mixing in mature compost to kick-start the decomposition, and watering down the whole mess to keep things nice and damp. The plywood bins are four sided, bottomless (they sit flush with the ground and have wire mesh strung across the underside, to allow air to circulate), and are topped with hinged lids. Currently the bins are home to quite a few earthworms, which are not ideal vermicomposting agents (more on this later), but they will break the litter in for the red worms to come.

First, what is vermicomposting? Taken from the Latin words verm, “worm”, and compositus, “put together” or “made up of”, vermicomposting is the process by which people harness the detritivorous aptitude of worms to make organic fertilizer for plants. Most terrestrial worms are detritivores, meaning that they consume detritus, or decaying plant and animal matter. Because this detritus is often mixed in with the soil, these worms essentially eat dirt, rely on the microorganisms in their gut to extract nutrients, and excrete little piles of further-decomposed matter as waste. These piles, called castings, are deposited outside the worms’ burrows, at the soil’s surface.

Castings are vermicomposting’s finished product. They are the leavings of the worms, but the gleanings of the farmer—one creature’s casts becomes treasure for the other. Worm casts, because they come directly from the worm’s microbe-rich gut, are ten to twenty times more microbially active than the surrounding soil, and the higher the microbe activity, the higher the overall rate of decomposition. When organic matter is decomposed like this, the nutrients within are broken down to their most elemental forms, and this is precisely what plants require. Plants need their food processed pretty thoroughly before their can make use of it—seeing as most lack any mechanisms to do so themselves—and worms perform the trick rather handily. Vermicomposting succeeds when worms and their minute allies work in tandem, breaking down raw organic material into a finely-textured, nutrient-packed matrix known as humus.

The worms best suited for vermicomposting are epigeal, meaning that their activity is mostly confined to the surface of the soil, where dead leaves and other decaying material are plentiful. Sometimes called “red wigglers”, these epigeal worms readily eat all kinds of compost, including food scraps and grass clippings. They thrive in worm bins, which ideally house a shallow layer of compostable material kept moist and oxygenated, and sheltered from weather and predators. The common earthworm seen wriggling across the sidewalk—the big ones yanked up by robins after a good rain—is an anecic species, burrowing deeper underground and preferring further-decayed fare than the red wigglers. They’re equally welcome in the garden for their casts, but they tend to tunnel out of worm bins before too long.

As the students tore newspaper into the bins, I quizzed them on their vermi-knowledge. How do worms move? “They wiggle through the dirt!” How do they breathe? “Through their skin!” Why are worms good for the garden? “They make dirt!” This last was a bit of an oversimplification, but it’s certainly true that worms provide an invaluable service to the production of arable soil—and without arable soil, agriculture is impossible. Even Charles Darwin in 1881 had this to say of earthworms: “It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures.” Worms enrich the earth, one cast at a time.

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