Don't worry about lawn bumps in the spring — it's probably a good sign

"Fielding Questions" columnist Don Kinzler explains why some lawn markings could indicate earthworm activity, and he answers questions about trying to save a potted tulip and using grass clippings as mulch.

nightcrawler mounds.jpg
Nightcrawlers are the likely culprit behind these bumps and mounds in a local lawn.
Contributed / Special to the Forum

Q: There are 2-inch-high bumps or mounds all over in our front lawn that terminate in a spot of bare earth. Do you know what they are? Could they be from earthworms, or maybe voles? — Shirley M.

A: Voles leave winding surface channels through the turf, so the mounds are not typical of vole activity. The dirt mounds do look like those caused by nightcrawlers or other earthworm species. The mounds are often more noticeable in the spring before fresh grass growth conceals the spots.

Earthworms, including nightcrawlers, are beneficial to the soil, as they provide natural aeration, allowing water and oxygen to penetrate more easily into the ground. As they move through the soil, they recycle nutrients and add fertilizer. Your lawn will be fine, and the little bare mounds will quickly fill in when grass growth begins.

Lawns affected by nightcrawlers become bumpy under foot, which is a common complaint. There are no pesticides that are labeled for control of nightcrawlers or other earthworms in the lawn. If bumpiness is an irritation, the bumps can be lessened by raking, power-raking or core-aerating the lawn.

Q: I’d like to use grass clippings as a mulch in our vegetable garden this summer. We do spray for dandelions in the spring, so I know you can’t use the grass clippings right after that. But I’ve heard that after two mowings you can save and use the clippings from the third mowing. Is that true? — David P.


A: The advice about using clippings from herbicide-treated lawns after two mowings is an old recommendation that is no longer safe to follow. Many herbicides currently used to control lawn weeds persist for long periods.

If any herbicides are used on a lawn, I wouldn’t use any of the clippings as a mulch in the vegetable garden. I receive heartbreaking emails every year from gardeners whose vegetable plants are curled, twisted and distorted from exposure to herbicides, either by drift from the adjacent lawn or from contaminated clippings used as mulch.

Lawn clippings make a great garden mulch. To keep them safe from contamination by herbicides, consider keeping the lawn free of weeds by digging, instead of chemical treatments.

Q: I bought a beautiful pot of blooming tulips at the florist. The leaves and flowers look very healthy, and I’m wondering if there’s any chance I can plant them outdoors this spring after they’re finished flowering? I hate to just throw the bulbs out. — Nancy D.

A: Tulips that are blooming in pots have expended the bulbs’ inner energy store. Tulips that are growing in flower beds spend the period after bloom recharging their strength and forming internal flower buds for the following year’s spring bloom.

Although it’s not a sure thing, potted tulips can sometimes bloom the following spring if planted outdoors. But there are several keys to success.

Apply water-soluble fertilizer right now to your potted tulips, and place in a sunny window. The nutrition and light are vital for recharging the bulbs’ energy and internal buds. Keep watering regularly, even after the flowers fade, so the leaves stay green and healthy for as many weeks as possible. When leaves begin to turn yellow naturally, stop watering and allow the plant to dry down.

When leaves are dry, brown and crisp, remove the bulbs from the pot and store in a dry location, such as a garage, and plant in a flower bed after midsummer. The plants should emerge next spring, and if the bulbs recharged themselves sufficiently, you’ll enjoy both foliage and flowers. If you get only leaves and no flowers, the potted bulbs didn’t recharge their energy enough.


If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at
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