Garden allies: A worm’s eye view

Barbara Faurot Garden Notes
Posted 7/10/24

Healthy soil is the foundation of a flourishing garden. One of the best ways to build and improve soil is to encourage beneficial earthworms. 

Earthworms can be surface dwellers, topsoil …

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Garden allies: A worm’s eye view


Healthy soil is the foundation of a flourishing garden. One of the best ways to build and improve soil is to encourage beneficial earthworms. 

Earthworms can be surface dwellers, topsoil feeders, or deep burrowers. They leave behind castings rich in nutrients and create tunnels for air and water to penetrate into the soil. The tunnels improve drainage and soil structure while offering a haven for beneficial microbes. The worms and microbes break down decaying leaves, roots, and other organic debris into smaller particles that can be readily absorbed by plants.

There are several hundred species of earthworms in North America. Most native earthworms were scraped away with the topsoil during the last glaciation more than 10,000 years ago. Today’s common earthworms were introduced by European settlers from rocks and soil used as ship ballast and imported plants. Most play an essential role in ecosystem health. 

In the home garden, encourage beneficial earthworms by using organic mulch around plants – arborist chips, straw, conifer needles, or shredded leaves – to provide nutrients and shelter. Add compost to provide a food source for the worms. Layering compost and mulch on top of the soil also promotes consistent soil temperature, helps retain moisture, and suppresses weeds. 

Plant cover crops like crimson clover or annual ryegrass in between planting seasons to add organic matter to the soil. Create a welcoming environment by minimizing soil disturbance and avoiding chemical fertilizers that can harm beneficial earthworms. 

Worm compost, also known as vermicompost, is another great way to feed plants and improve soil. Red wigglers (Eisenia fetida) and red worms (Lumbricus rubellus) are especially effective in recycling organic waste into compost. While regular compost is broken down by microorganisms and heats up during decomposition, vermicompost is created by worms and microorganisms in a cooler process, indoors or outdoors (55°-77°F is ideal). 

Small microorganisms break food bits into small enough pieces for the worms to eat. The result is a finer textured worm compost rich in plant nutrients and beneficial microbes. Nita Wester, WSU Extension Master Gardener and co-instructor of WSU’s Growing Groceries class, explains that “red wigglers are suited to living in the crowded conditions of a worm bin, so they create lots of nutritious castings for your plants.” Most other earthworms require more space. 

Wester adds that “the reason I love red wigglers is they make a fertilizer that’s better than anything you can buy. The vermicompost helps keep plants healthy by concentrating the number of nutrients and microbes and creating more fertile soil.” There is also evidence that using worm compost in the garden can help with some plant diseases. 

Setting up a worm bin at home can be done in a small space and is relatively simple and inexpensive. Use almost any type of ventilated container, biodegradable bedding material like shredded newspaper, and organic matter such as fruit and vegetable scraps, coffee grounds, tea leaves, eggshells, and plain grains. A well-tended worm bin is odorless and, as Wester says, “they’re very little trouble.”

Jumping worms (Amynthas spp.) have become a problem in some Northeast, Midwest, and Southeast states. Native to East Asia and introduced to North America about 100 years ago, they are not widespread in the Pacific Northwest, but a few have been detected in Oregon and Washington. The jumping worms live near the soil surface and can rapidly deplete organic matter, destroying the soil structure and nutrient content. When they process the soil, the remaining mix looks somewhat like loose coffee grounds. 

There have not been any confirmed cases of Asian jumping worms in Jefferson County, but “prevention is key to keep out unwanted species,” says local entomologist Richard Lewis. Worms and their cocoons, which are egg sacs that contain one to many eggs, can spread by moving contaminated soil, fishing bait, mulch, plants, or tools. “Vigilance is key for early detection and management,” adds Lewis. 

The jumping worms can be identified by their erratic behavior — violently thrashing and jumping around compared to the slower, wriggling movement of earthworms. Common earthworms are typically reddish-brown or pink with a distinct, saddle-shaped clitellum — the raised, thickened band where they produce cocoons.

In contrast, the jumping worms are darker brown or gray, and can be distinguished by a large mouth and a lighter colored, smooth clitellum present in segments 14-16 (counting from the mouth end of the worm). The clitellum goes all the way around the worm and is flush to the rest of the body.

There is some evidence that adding biochar to soil might help eradicate adult jumping worms due to its abrasive properties. Hand removal, solarization, and applying tea seed meal have also shown some promise. 

Barbara Faurot is a Jefferson County Master Gardener and Master Pruner, working with other volunteers who serve as community educators in gardening and environmental stewardship.