Earthworms Are Gardeners’ Unseen Helpers
Durango Herald October 12, 2003
Leigh Gillette

Want a better garden, orchard, or lawn next year? Encourage earthworms now! These amazing creatures literally eat their way through the soil, fertilizing it as they go.

When soil passes through a worm’s gut, organic matter is digested and changed into forms that are ideal for plants. Worm manure or “castings” have been shown to have 5-11% more plant-friendly nitrogen, phosphorus, and potassium than the originally consumed soil.

While there are an estimated 4,400 species of earthworms in the world, they can be divided into two basic types: earth workers and composters. Earthworkers tunnel through soil, and are the earthworms seen commonly in Colorado. The nightcrawler, Lumbricus terrestris, is an earth mover that can measure from 4” to an amazing 12”! Aptly named, naightcrawlers come above ground at night to mate, search for food, or leave castings (looking like tiny coils of brown mud). Nightcrawlers often drag dead leaves back into their burrows to feed, safely hidden from light, predators, and dry air. While constructing their burrows, the worms and bring minerals from deeper soil levels to the surface. The burrows also let water percolate, and air reach plant roots. Nightcrawlers and other earthworkers are most active during the spring and fall, when soil moisture is ample, and soil temperatures cool. During summer droughts or winter freezes, these worms coil up in deeper burrows, and become dormant until conditions improve.

Compost worms,In contrast with earthworkers, do not live in soil. Instead, they inhabit pure organic matter. Because our native soils are often dry and low in organics, compost worms are seen infrequently. But these composters, especially the red wiggler (Eisenia fetida), are found thriving in manure piles, compost heaps, and even indoor “worm composting bins”, eating their body weight each day in yard and kitchen waste, and producing castings that are second to none!

How can a gardener encourage a thriving earthworm population? According to a Colorado Master Gardener fact sheet (www.cmg.colostate.edu/factsheets/soil), earthworms prefer soil that is 40ºF to 70ºF, a bit damp, and rich in organic matter. Mulching can provide these conditions. Clippings can be left on the lawn, and garden beds can be thickly covered in leaves. The mulch layer insulates the soil, prevents moisture loss, and provides ample food for the worms. Stirring compost into the soil provides even more nutrition.

While mulching encourages worms, harsh chemical application discourages them. Earthworms, while able to eat all manner of decomposing plant and animal materials, are intolerant of most inorganic fertilizers and pesticides. These chemicals either force worms to vacate, or kill them outright. (Fortunately, pyrethrins used to deter mosquitoes are harmless to earthworms).

Learn more about earthworms from The Earthworm Book by Jerry Minnich, and Worms Eat My Garbage by Mary Applehoff.