As worms turn, our gardens continue to grow

Have you ever wished you had a helper who could till the garden, turn the compost pile and add free fertilizer to it without you doing much of anything?

Chances are you already have such a helper and you may not even have noticed: Earthworms are the unsung and underappreciated heroes of the garden.

These little wriggly critters are nature’s most powerful ally in creating soil texture, happily chewing their way through the top layers of soil looking for a meal of compost, fungi or other organic material. They break down organic matter for other soil microbes and mix and loosen soil particles so air and water can get in.

As they quietly work away, they release nitrogen and other nutrients that our plants need. If worms were not present in the soil, it would be nothing more than a hardpan with no air spaces, no capacity to hold water or support much plant growth. By one research estimate, worms can process 16,000 pounds of soil per acre per year; 30,000 pounds if there are lots of them.

For all their power in moving soil, earthworms are very simple creatures. Their long, thin bodies are perfect for going through narrow tube tunnels aided by a simple brain that controls little more than the contraction and elongation of different sets of muscles to move them through the soil. In fact, the brain is so simple that if it is removed, there is little effect on the worm’s general behavior

Worms “see” through a series of light-sensitive cells in their skin. When they are hit with light, the cells tell them to head underground so they don’t dry out on the surface. This is why they wiggle so wildly when we turn them up in the dirt. They breathe by infusing oxygen directly through their skin from air or water. This is why you technically speaking can’t drown a worm.

According to Mary Fauci, an agricultural research technician at Washington State University, most of the worms we commonly find in our soil hitchhiked here on the plants our European ancestors brought with them to the New World, and then moved west with American settlers.

“People dug up a plant and brought it with them to their new home. They carried cocoons or live adult (worms) with them that way, or in mud on boots,” says Fauci.

Researchers believe that most native worms in the northern part of the U.S. were probably killed off during the last glacial period that ended about 10,000 years ago. Even though earthworms can survive being frozen quite nicely during a normal winter, the extended bitter cold and pressure of the ice was too much. Because our region was at the edge of the glacial zone, there were only a few known native worms left, says Fauci.

There are three major types of worms commonly found here:

Night crawlers, the largest at eight to ten inches, dig deep vertical burrows between the subsoil and the surface of the ground. They come to the surface at night and collect organic material, pulling it back into their burrows. They often leave a little pile of castings at the top of their burrow to seal it from drying air and heat. These worms are common in moist areas under trees where the soil is not regularly tilled.

Garden and manure worms, are the varieties we commonly turn up when gardening or adding manure to the garden, they grow to get five to seven inches long and they live in the top foot or so of soil. They, like all worms, are most active in the spring and fall when the soil is comfortably warm. In the winter and the hottest part of the summer, they retreat deeper into the ground and go into hibernation. In the winter, they will actually freeze in the soil.

Red wigglers are common in compost piles and are only about three to four inches in length. These are the easiest worms to raise in captivity and are what you get when you buy worms for a compost pile or a worm box.

Encouraging worms to grow in your garden is relatively easy.

“Add lots of organic matter,” says Fauci. “It’s their preferred food and they will migrate in from other parts of the yard.” And leave them alone to do their job.

“Keep mechanical rototilling to a minimum,” Fauci says, adding that tilling shouldn’t be done more than once a year and then only enough to break up the soil. “Don’t till until the soil gets to a powdery state,” she says.

Tilling too much breaks up the worms’ tunnels and can cause a significant mortality rate.

“Contrary to some beliefs, cutting a worm in half does not make two worms, it kills it,” she says.

Pesticides can affect worms close to where the chemicals are applied so it’s best not use them any more than necessary. Because worms eat fungi in the soil, fungicides can affect them as well.

The Inland Northwest does have one significant native worm says Fauci, the Palouse giant earthworm. The worm was up to 18 inches long and white in color. It was commonly found in agricultural fields. “It hasn’t been confirmed in collection since the late 1970s,” says Fauci. “If anyone does find one, they should call me.”