Earthworms are natural architects of healthy soil, and encouraging their presence improves garden health. By burrowing and feeding, these organisms enhance soil aeration and drainage, allowing plant roots to penetrate deeper into the substrate. As they consume organic debris, earthworms excrete nutrient-rich castings, helping to cycle nutrients like nitrogen and phosphorus back into an accessible form for plants. Increasing the earthworm population involves optimizing the soil’s physical environment, ensuring a steady food supply, and protecting the worms from external harm.
Enhancing the Garden Habitat to Attract Native Worms
Creating a welcoming environment for native earthworms begins with addressing the physical conditions of the soil they inhabit. Earthworms require consistently moist soil because they breathe through their skin and can quickly dehydrate if their environment dries out. The soil should remain damp, similar to a wrung-out sponge, but never waterlogged, which would deprive the worms of necessary oxygen.
Soil structure is also an important factor, since worms struggle to move through heavily compacted ground. Preventing soil compaction encourages worm movement and burrowing, which improves soil porosity and stability. Furthermore, a healthy worm population is highly sensitive to chemical inputs. Eliminating synthetic fertilizers and pesticides is necessary, as highly acidifying fertilizers like ammonium sulfate and certain fungicides can drastically reduce earthworm numbers.
Providing Sustainable Food Sources for Worms
Once the physical environment is optimized, a continuous supply of organic matter must be introduced as the worms’ primary food source. Earthworms consume decaying plant matter and the microorganisms that colonize it, turning this debris into beneficial soil castings. A generous layer of surface mulch, such as shredded leaves, grass clippings, or straw, provides an accessible food source for surface-feeding species like nightcrawlers.
Incorporating compost directly into the garden beds feeds the worms while simultaneously improving the soil’s moisture-holding capacity. Aged manure from plant-eating animals, such as cows or horses, is excellent, but it must be properly composted to avoid excess ammonia or pathogens. Coffee grounds provide nitrogen and are easily digestible. Crushed eggshells can also be added to provide calcium, which aids in worm reproduction and helps balance soil acidity.
Introducing Worms: Sourcing and Release
If a garden lacks a robust native population, introducing worms may be necessary, but correct species selection is crucial. The common garden worm, or nightcrawler (Lumbricus terrestris), is a deep-burrowing species that creates permanent vertical channels, making it ideal for improving garden soil structure. In contrast, red wigglers (Eisenia fetida) are shallow-dwelling composting worms that primarily live in surface litter and require a constant, rich food source to thrive in garden soil.
Garden worms should be sourced from specialized suppliers and introduced in small batches for acclimation. The ideal release time is at night or during an overcast day when temperatures are mild, as worms are sensitive to light and heat. Spreading the worms gently onto the soil surface, under an existing layer of mulch or compost, provides immediate protection and access to food as they begin to burrow.
Protecting Worms from Predators and Stressors
Long-term retention of a healthy worm population requires management strategies that minimize disturbance and insulate the soil from environmental extremes. The practice of no-till or minimal-till gardening is beneficial, as traditional tilling destroys established burrows and can injure or kill the worms and their eggs. Leaving the soil structure intact allows deep-burrowing species to maintain their tunnels, which can survive for many years and significantly improve water infiltration.
Managing soil temperature is important, as earthworms are most active between 50 and 86 degrees Fahrenheit. Applying a thick layer of organic mulch acts as an insulating blanket, moderating soil temperature and protecting worms from extreme heat and freezing conditions. While natural predators like birds and moles are unavoidable, maintaining a dense surface cover of mulch offers protection, especially when tilling is reduced, which otherwise exposes the worms to easy predation.