The Benefits of Earthworms and How to Attract Them

Joel Salatin is in awe of the benefits of earthworms and worm castings on Polyface Farms, where the hard-working critters boost soil health and increase farm productivity. He offers tips on how to attract earthworms to your farm or homestead.

Soil and Worm

Worms aerate soil as they burrow, and deposit mounds of fertile castings when they emerge.

Photo by Dwight Kuhn

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What fascinates you? What warrants your fixation? At the risk of being dismissed as certifiably weird, may I humbly submit the earthworm as deserving of both fascination and fixation? Raise worms and reap a copious crop of worm castings, which will improve soil health and increase aeration, all while holding true to no-till, organic agricultural principals.

When my parents purchased farmland in Virginia’s Shenandoah Valley in 1961, the soil was thin, infertile and completely unproductive. Not a single earthworm was to be found. Today, several inches of new topsoil support vibrant farm production and high earthworm populations.

In many ways, earthworms are a litmus test for soil fertility. Anyone who farms or gardens should be awed by these fertility facilitators. Several icons in the sustainability movement have been students of the lowly earthworm — Sir Albert Howard, J. I. Rodale, Bill Mollison.

Howard pointed out many benefits of earthworms, noting that earthworm tunnels provide ventilation for air and water to penetrate the soil, and that earthworms “condition the food materials needed by the roots of plants.” Howard went as far as to call earthworms “the ideal soil analysts,” claiming they can “furnish the gardener with a report on the state of his land far more instructive than anything the soil scientist has so far provided.”

The Dirt on Earthworm Anatomy

An earthworm is a sightless creature with a gizzard, an alimentary canal, and a body made of rings surrounded by bristles. Earthworms don’t move by zigzagging like snakes. Rather, they compress and expand with their rings and bristles, moving straight through the soil.

Most people think ants are strong for their size, but earthworms are the ultimate hulks. Weighing only one-thirtieth of an ounce, they routinely move 2-ounce stones — equivalent to a 150-pound person moving a 9,000-pound boulder.

What I find most amazing about earthworms, and indeed what still baffles scientists, is that the castings that come out of the worms’ alimentary canals contain five times the nitrogen (N), seven times the phosphorus (P) and 11 times the potash (K) of the soil environment in which the worms live. It’s almost like alchemy because no net loss occurs.

This is not a case of taking a lot and excreting a little. This is recombining — what Howard called “conditioning” — vegetable matter and minerals into a perfect fertility capsule.

In addition, the worms’ alimentary canals detoxify the materials they ingest, offering a truly clean, pathogen-free casting out their back ends. Earthworm castings are the magic elixir coveted by good gardeners and farmers all over the world.

Depending on which researcher you read, a healthy earthworm population can create a half-inch to an inch of fertile topsoil every five years. This is no small feat.

Manage Your Soil for Earthworm Success

At the beginning of this column, I mentioned that I couldn’t find a single earthworm on our farm when I was young. Now, I have to be careful how I walk across the fields to keep from turning my ankle on earthworm casting mounds! OK, that may be a bit hyperbolic, but we do have 2-inch-tall mounds everywhere. Indeed, we’ve had visitors bring recording equipment to capture the sound of earthworms retreating into their tunnels as we walked along.

What changed? How do you attract these healers of the Earth, these builders of soil? We never purchased earthworms or inoculated our fields with earthworm cocoons.

Few beings are as resilient as earthworms. Both they and their eggs can lie dormant while in inhospitable conditions. Then, when conditions change, they can come to life, hatch, and be productive.

Folks who study earthworms agree on several key elements. First, earthworms thrive in cool, dark, damp conditions. They prefer a Goldilocks environment: not too hot, not too cold — just right.

Denuded soil — caused by clean tillage, dirty chicken yards or overgrazing — is the quickest way to destroy healthy earthworm populations. Vegetation is the protective covering of the Earth. Seeds — carried on the wind, and on feathers and hides of animals — lay dormant in the soil, where they constitute an insurance policy against bare earth.

Have you ever moved an old board that’s been lying on the ground, undisturbed for months, only to discover a dozen fat, beautiful earthworms dwelling underneath? The board protects the soil from drying out and ensures a dark, cool environment.

This is why mulching, whether with vegetation or black plastic, encourages earthworm activity. It’s also why deep, lush pastures created by rotational grazing stimulate earthworms. If you have a plot where a horse, cow, goat or chicken — name your critter — stays all the time and keeps the foliage pruned to ground level, the earthworms will leave or go dormant. But, if you can allow the forage to grow to its phenotypical zenith, or full expression, the dense canopy will act as a mulch to cool down, darken and moisten the soil.

How to Attract Earthworms

Some of the most abused land in the world is in backyard lots where daily animal impaction hardens the soil and denudes it of vegetative cover. If we’re actually going to heal land — and I believe this is our human imperative — then we must provide a habitat that encourages earthworms. A deep, vegetative cover moderates soil temperatures in early spring and late fall, when exposed soil cools down too fast or warms up too slowly. Earthworms like damp environments, but neither dry nor wet. They like cool environments, but not cold. The thicker the soil canopy, whether living forage or dead carbon (wood chips, leaves or straw), the easier it is to maintain those parameters.

Manure and compost also stimulate earthworm proliferation. This, of course, raises the question: Can a farm without animals be a worm-friendly place? You could certainly import manure-based compost, as long as transportation energy remains relatively cheap, but, ideally, you’ll want to include livestock in any sustainable farm plan.

Remember, nature has no animal-free ecosystems. Perhaps one reason is that animals feed and encourage healthy earthworm populations. Chemical fertilizers, pesticides and herbicides, on the other hand, are not conducive to earthworm health and activity. Some may argue that increasing vegetative growth through chemical fertilization does increase earthworm activity. While that might be partially true, these acid-based nutrients are toxic to earthworms, and the additional plant growth is all that buffers the damage.

Apply nothing to the soil that an earthworm can’t eat. And, we shouldn’t apply anything deadly to an earthworm. Fortunately for those of us who compost on a large scale, earthworms can take a relatively rough or unfinished material and finish it in the soil. Here at Polyface, we don’t worry about making perfect compost that looks like potting soil. As soon as the compost smells sweet and humusy, we spread it and depend on earthworm diligence to finish its conversion to root-ready goodies.

Using No-Till, Organic Practices for Worm Health

Earthworms enjoy undisturbed soil. Tillage not only chops up many worms, but it also destroys their tunnels. This is why most of the best gardeners today practice shallow tillage, no tillage, broadforking or combinations of these. The point is that deep “eggbeater” tillage and soil profile inversion are too disturbing to the earthworm community.

This is certainly one of the benefits of permaculture, which minimizes tillage by encouraging perennials rather than annuals. Anything we can do to decrease aggressive soil disturbance will leave earthworm tunnels and communities intact. My friend and sustainable entrepreneur Bill Wolf says, “Earthworms like to be fed on top of their heads.” In other words, the idea that we need to aggressively till in order to place organic matter near earthworms’ accommodations is simply opposite of what they want.

Earthworms burrow, sometimes as deep as 12 to 14 feet, bringing minerals from down deep, depositing them on top of the soil, and taking organic materials back down into the earth. You can encourage this industrious and meticulous activity with compost, manures, and living and nonliving covers, rather than impeding it with inappropriate, aggressive tillage.

I never tire of getting down on my hands and knees in lush pasture, parting the forage, and finding mountains of worm castings. Visitors are often astonished, having never seen casting pillars. And that awe is well-deserved: Ultimately, a civilization’s health is dependent on protecting the health and vibrancy of its earthworms.

Joel Salatin and his family manage earthworms, grass and livestock at Polyface Farms in Swoope, Virginia. Joel is the author of Folks, This Ain’t Normal, as well as numerous other titles related to local food and sustainable farming.