Worms: Mighty soil-makers

Earthworms work tirelessly to improve soil. — pfly/Flickr

Earthworms work tirelessly to improve soil. — pfly/Flickr

Do worms make you squirm? Do you think of them, if you think of them at all, as slithery little denizens of the netherworld, crawling witlessly around in the dark? Would you perhaps even characterize them as unlovely and inconsequential?

If so, it’s time for an attitude adjustment.

The lowly earthworm deserves not only your respect, but your gratitude, too. Earthworms work tirelessly to improve soil structure and fertility, transforming bits of organic debris and small particles of soil into a nutrient-rich substance than enhances plant growth.

Without earthworms, it would take 100 to 150 years for natural forces like erosion to produce a single inch of topsoil. Earthworms can produce that same inch of fertile, friable growing medium in just a year. If you enjoy the fruits of the soil, the bounty of the harvest, you can’t dis the worm.

The father of oligochaetology (the study of worms) was no lesser a light than Charles Darwin, more famously known for his theory of evolution. His last book, published in 1881, summarized some 40 years of intimate research into earthworm behavior. “The Formation of Vegetable Mould Through the Action of Worms, With Observations on their Habits” included some startling conclusions.

Virtually all of the world’s fertile land has passed many times through the gut of earthworms, nature’s original plough, Darwin proposed. Given their recycling of organic nutrients to the benefit of agriculture, he “doubted whether there are many other animals which have played so important a part in the history of the world.” Take that, you fickle housecats and clever sheepdogs.

Darwin estimated that an average acre of garden soil contained some 50,000 worms generating 18 tons of manure or castings every year. In fact, their numbers vary quite a bit more than that, ranging from 20,000 per acre in the flinty soils of Romania to 8 million per acre in a New Zealand pasture. Wherever you are — short of a paved city street or shopping mall parking lot — the earth really is moving under your feet.

Uniquely suited to a life underground, the slender earthworm burrows through the earth to depths of eight feet and more, leaving behind channels that let essential air and moisture into the zone where plant roots live. By alternately elongating and shortening its segmented body, helped along by stiff hairs known as setae and lubricating mucous, the worm can penetrate soils that defy assault by shovel-wielding humans.

As it goes about its work of foraging, the worm drags leaves, pine needles and other detritus into its burrow, facilitating the decomposition of organic debris that returns to the soil elements consumed by plants. But the benefits of worms don't end with tilling the soil and recycling decaying plant matter.

The worm's output — call it manure, castings or worm poop — is a high-quality organic fertilizer rich in basic plant nutrients, humic acid, trace elements and beneficial micro-organisms. Odorless and innocuous in appearance, looking much like a handful of finely screened compost, castings are pure garden gold, created through the alchemy of a worm's humble transit through the soil.

Vermicomposting puts captive worms to work for you. — CAFNR/Flickr

Vermicomposting puts captive worms to work for you. — CAFNR/Flickr

"Their work may seem unspectacular at first," writes Amy Stewart in her fact-filled homage "The Earth Moved: On the Remarkable Achievements of Earthworms" (Algonquin Books). “But they do something powerful: they consume, they transform and they change the earth."

Earthworms are every gardener's silent partner, their presence a measure of soil fertility. But which worms, exactly, do we find most useful?

While North America has about 100 native species of earthworms (and the world some 5,500), three European species are today the commonest: the nightcrawler, the red wiggler and the red worm. Their invasion was accidental and unnoticed as they hitched a ride to the New World in the potting soil, ship's ballast and livestock bedding of early settlers.

The nightcrawler Lumbricus terrestris — Darwin's worm — is hardy in our climate, burrowing deep into the ground to escape drought and cold winter temperatures. The red worm and red wiggler, Lumbricus rebellus and Einsenia foetida respectively, also play a starring role in soil improvement but can't live year-round in our garden soils since they need higher temperatures to live and breed.

These latter two represent 80 to 90 percent of the worms produced commercially for vermicomposting — maintaining a colony of worms in a bin to consume vegetable waste and produce nutritious castings. A classic on the subject, Mary Appelhof's "Worms Eat My Garbage" (Flower Press) has been in print since 1982 and will tell you everything you need to know about setting up a worm composting operation.

If you want to encourage earthworms to inhabit your soil and do their good works, there are a few points to keep in mind.

Avoid deep and frequent tilling, since this destroys their burrows and can injure those caught under the blades. A worm cut in two may regenerate its missing parts, but you won't get two worms from one; a section lacking a head is not a potential new worm but merely compost. Tilling also dries out the soil and speeds decomposition of organic wastes on which the worms feed.

Adding organic material, on the other hand, helps keep the worm population well fed. A layer of compost, mulch, chopped leaves or grass clippings will soon be incorporated into your soil with the help of actively feeding worms.

While herbicides pose little threat to earthworms, according to a study from the University of Wisconsin, pesticides can be deadly and should be avoided. Adding lime to acidic soils can help keep the pH reading close to the neutral point worms like.

Have respect for these soil-dwellers if you want a thriving garden. It couldn't easily happen without the lowly worm, transmuting ordinary organic waste into a potent plant growth booster. Inch by inch, one leaf and soil crumb at a time, the worm teaches us that even the humblest discards of the natural world can hold a glint of gold.