Understanding Earthworms

Earthworms, worm casting, and vermicomposting.

Photography by Christa Neu


worms are good for youThe pale red garden earthworm is often called "nature's plow." That's because an earthworm pushes through soft earth with the point of its head. If the soil is hard, the worm eats its way through, forming interconnected burrows, some several feet deep. Burrows loosen the soil, admitting air and water and helping roots grow. A single acre of cultivated land may be home to as many as 500,000 earthworms, each making the soil a better place for plants.

Earthworms in your garden
When you add nitrogen-rich compost to your soil, you help worms thrive. However, adding synthetic nitrogen fertilizers may repel earthworms. Worms are very sensitive to physical and chemical changes and will flee the salty conditions that result from an application of chemical fertilizer.

As an earthworm feeds, organic matter passes through its body and is excreted as granular dark castings. You may see these small casting piles in your garden. An earthworm produces its weight in castings daily. Worm castings are a wonderful fertilizer, rich in nutrients otherwise unavailable to plants.

In cold weather, a soil search will turn up mature and young earthworms as well as eggs. By late spring, most worms are mature. As temperatures rise, activity slows; many lay eggs and then die. By midsummer, most worms are very young or protected by egg capsules. As the weather cools, young worms emerge. With wet weather, they grow active, making new burrows and eating extra food, resulting in more worm castings. Egg laying occurs again. Activity continues as long as soil stays damp.

After a heavy rain, earthworms often appear aboveground. They haven't drowned. Fresh water doesn't disturb earthworms—they need ongoing skin moisture to breathe—but stagnant or contaminated water forces them from their burrows.

Earthworms can survive in soil that freezes gradually, but sudden freezing can kill them. Protect earthworms against sudden freezes with mulch or a cover crop, both of which also provide worms with food.

Earthworm Bins
You can raise earthworms yourself using purchased redworms—a process called vermiculture or earthworm composting. Kept in a cool, dark place, such as a basement, a worm bin provides a composting system for kitchen scraps and a source of rich, fertile worm castings for the garden.

Commercial bin systems. Commercially available bins are typically made from durable black plastic, with trays that fit on top of a base. The trays have mesh bottoms for drainage, and the base catches "worm tea" and dispenses it from a spigot so you can use it to water your plants. A top keeps light out and worms from escaping. You fill the lowest tray with a moist filler material (usually a soaked coir fiber brick and/or shredded paper, with a little compost or garden soil mixed in to provide beneficial organisms). The filler should be uniformly damp but not wet, just like any working compost pile. Once you add the worms, you can begin adding kitchen scraps every day or so as the worms consume them, transforming them and the filler into nutrient-rich castings. As with any compost pile, keep meat, fats, and dairy products out of the pile. Coffee grounds and filters, tea bags, oatmeal, bread, and fruit and veggie scraps are excellent worm compostables.