What is Causing Mounds and Tunnels in My Yard?

Are areas of your lawn bumpy and uneven? When you walk across these areas does the soil sink or feel soft? If so, some type of soil dwelling critter is probably the cause. During winter the activity of moles, earthworms, and mole crickets can cause mounds and tunnels in lawns that result in uneven or rough patches. To fix these problem areas you must first diagnose which critter is causing the damage.

Earthworms

Earthworm castings in turf.

Earthworm castings build up in small mounds that rarely reach over an inch high.

Earthworms are extremely beneficial for lawns and gardens. As they tunnel through the ground they create channels that allow air and water to move into the soil and improve drainage. In addition, earthworms ingest soil and organic matter, which passes through their digestive tracks and comes out the other end as worm poop, more commonly referred to as worm castings. Worm castings are an excellent source of nutrients for plants and are sometimes sold as a natural fertilizer.

Earthworms are active near the soil surface during fall and winter, particularly when the ground in wet. As a result, their castings can build up in mounds that resemble small ant hills. To determine if the mounds in your yard are caused by earthworms look at the size of the soil particles. The soil from mounds caused by ants and burrowing insects is usually very fine, composed of individual soil particles or sand grains. The soil from mounds created by earthworms is clumped into pellets that resemble Nerds candy, except they are the color of soil.

High earthworm populations are more common in moist, heavy soil. In these soils, worm castings can sometimes build up an inch or more deep, particularly in winter when the lawn is not being mowed. The good news is the earthworms and their castings almost never cause damage to the lawn and there is no need to try to get rid of them. If castings become thick in an area of your lawn simply rake them out or collect them and use them as a natural fertilizer in other areas of your yard.

Mole Crickets

While earthworms tunnel down into the ground feeding on soil and organic matter, mole crickets tunnel just below soil level and feed on grass roots, causing serious damage to turf. High populations of mole crickets can kill areas of turf, leaving bare soil that may be crisscrossed with narrow, pencil sized tunnels. Where mole cricket activity is very high, the soil can appear churned up and feel soft or spongy underfoot.

Mole crickets are a common and serious lawn pest in the south. The damage caused by mole crickets is sometimes incorrectly attributed to white grubs, though white grubs rarely cause serious damage to lawns in our region. Areas damaged by mole crickets can be raked level and reseeded or sodded in spring. These areas should be marked and treated in early summer since mole crickets frequently reoccur in the same area from one season to the next.

Moles

Eastern mole

Moles tunnel through the soil with their large, paddle like front paws.

Moles tunnel through yards in search of soil dwelling insects and earthworms to eat, leaving lawns potholed and uneven. Unfortunately there is no simple, easy way to get rid of moles. Home remedies, sonic devices, and castor bean oil have little effect. Broadcasting pesticides throughout your lawn to kill soil dwelling insects is sometimes touted as way to reduce mole damage but this is rarely effective and not recommended. Trapping is the most reliable method of mole control, but requires careful observation of tunneling activity to determine where to place the trap.

Mole activity is most noticeable in fall and early spring. Areas damaged by moles should be tamped down by foot or flattened with a lawn roller. Turf in these areas will often recover on its own. If reseeding or sodding is needed, the best time to do so is March through May. Learn more about moles from this past Pender Gardener article.

Learn More!

Use Extension Search to find research based information from Cooperative Extension systems across the U.S.

Visit your local Cooperative Extension office to learn more about gardening and landscape care. Go to http://www.ces.ncsu.edu/local-county-center/ to find your county Extension center or post your questions to be answered online via Extension’s ‘Ask an Expert’ widget.

Contact your local Cooperative Extension office to get expert advice from an Extension Master Gardener Volunteer:

Visit the Pender Gardener blog to stay up to date with all the latest gardening news, or sign up to receive weekly gardening updates through our email news services:

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Written By

Charlotte GlenExtension Agent, Agriculture - Horticulture (919) 542-8202 (Office) Chatham County, North Carolina

Posted on Jan 18, 2013

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