- Symptoms of lawn mumps include the appearance of lumps and bumps in your turfgrass. These bumps are known as "middens," and consist of plant residue and worm excrement, or castings, from nightcrawlers. Nightcrawlers are large, reddish-brown worms that grow up to 8 inches long. They build burrows in the soil that can be 5 or 6 feet deep, and a midden appears at the surface of a burrow. At night, a nightcrawler comes to the surface of its burrow and pulls food down inside to feed on later. Middens aren't harmful to your grass, but they can make mowing difficult. Lawn mumps usually appear during spring and fall, when worms are closer to the surface. In summer, when the soil dries out, the worms burrow deeper into the ground.
- Earthworms serve many useful functions. They return nutrients to the soil by feeding on thatch and helping it decompose. Their castings help fertilize the soil. They also aerate the soil, which allows water and oxygen to penetrate into the ground and makes nutrients more available to your grass. The presence of earthworms indicates healthy soil. Killing them is not desirable, and there are no legal chemicals registered for controlling them.
- You can reduce the activity of nightcrawlers in your lawn by giving your lawn a good soaking once a week rather than frequent, light waterings, because shallow watering encourages nightcrawlers to stay near the surface. Encourage birds that feed on nightcrawlers to visit your yard by installing birdfeeders and birdbaths. You can also increase the acidity of your soil; earthworms don't like acidic soils with a pH less than 6.0, so using acidifying fertilizers such as ammonium sulfate or ammonium chloride can reduce activity from worms.
- Break up existing bumps with a power rake. Power rakes, or dethatchers, resemble lawn mowers with vertical blades, and are used to remove thatch. You can rent one from a garden center or rental company. Power raking should be done in spring or fall, not in summer when it will injure growing plants. If you power rake in spring, use a pre-emergent herbicide to keep weeds from sprouting. Don't use a heavy roller to remove bumps from lawns, because it compacts the soil, impeding root growth and making it more difficult for grass to take up water and nutrients. Eventually, this leads to a thinner lawn.
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