Worms! Soil-building Workhorses

Image Gallery A night crawler pulls a leaf to its burrow. DWIGHT KUHN

Vermicompost, or compost made mostly by earthworms, is seven times richer in plant nutrients compared to compost created mostly by fungi and bacteria, and recent studies suggest that small amounts mixed into soil suppress diseases, slugs and insects. Numerous studies have shown that when only 10 percent of the volume of potting soil used to grow seedlings is vermicompost, a huge range of plants simply grow better — from carrots to tomatoes to zinnias. It’s easy to entice earthworms to work their magic right in your garden, or you can make vermicompost in enclosed bins, or both! In addition to improving soil chemically with their castings (a mixture of manure and slime emitted through the worms’ skin), earthworms improve it physically by opening airways and drainage holes as they travel.

Notice that I did not tell you to buy worms. That’s because we’re recommending “catch-and-release” worm composting, which makes use of the earthworms present in your own yard. These species have already demonstrated their satisfaction with your unique climate and soil, though few (or none) of them are likely to be red wrigglers (Eisenia fetida), the species used in commercial vermicomposting systems. That’s ok. Common red worms (Lumbricus rubellus) and other species plucked from compost bins or soil (or rescued after flooding rains) usually make well-behaved captives, and you can usually coax larger night crawlers (L. terrestris) to colonize any spot by piling on plenty of mulch.

Indeed, when it comes to using earthworms to build soil fertility, Clive Edwards, Ohio State University entomologist and author of Earthworm Ecology — the academic bible on earthworms — thinks night crawlers deserve top priority. “The best thing is to obtain some L. terrestris and inoculate your garden with them. They are the most important species in promoting soil fertility,” he says.

Night crawlers are widely available as fishing worms, but before you buy any, try these simple setups to give resident night crawlers a helping hand.

Maintain permanent pathways that are mowed or mulched, so there is always a layer of decomposing litter at the surface. Night crawlers build semipermanent burrows, where they stockpile food gathered at night. Providing safe year-round habitat is essential to keeping populations high.

Use the spaces between widely spaced squash or melons as night crawler condos. Place wet newspapers or cardboard over the surface (they love the shelter), sprinkle raw oatmeal over the newspapers (they love the food), and top with 2 inches of coarse, moist compost. Repeat the layers and top off with grass clippings, straw or another attractive mulch. If you build it, they will come.