We get this question constantly. “What are all these little bumps in my lawn?” If you have bumps in your lawn, here’s the good news: it’s almost always a sign that your soil is alive and healthy. The bumps are earthworm castings, and they tell us something important about what’s happening below the surface.
What’s Actually Causing the Bumps
Earthworms (especially nightcrawlers) eat their way through the soil and leave behind small mounds of digested material called castings. The castings come up moist and look like little mud balls. As they dry out in the sun, they harden into the small dirt mounds you can feel under your feet.
Flick the top of one of these mounds and you’ll usually find a small hole, often up to about 1/4″ wide. That’s the worm’s tunnel. Nightcrawlers make the biggest mounds. Smaller worms make smaller ones. In Maine, we see the most casting activity in spring and fall when soil moisture is high and temperatures are mild.
Why Bumps Are Actually a Good Sign
An earthworm-active lawn is doing exactly what a healthy lawn should be doing.
- Natural aeration. Worm tunnels relieve soil compaction and let air, water, and roots move freely. They do for free what mechanical aeration costs hundreds of dollars to deliver.
- Better moisture penetration. Water reaches the root zone instead of running off, which matters in our often-droughty summers.
- Microbial activity. Castings are loaded with the microbes that break down thatch and feed turf roots.
- Free fertility. Worm castings are one of the most balanced natural soil amendments on the planet. Gardeners pay for this stuff in bags. You’re getting it for free.
For homeowners worried about treatment programs harming worms, you can rest easy. The treatments we use as part of our turf management program have no meaningful effect on earthworm populations. We’ve watched the same properties stay loaded with worm activity year after year on our programs.
So What Do You Actually Do About the Bumps?
The honest answer is: not much. The bumps come with the benefit, and the benefit is huge. The right play is to mask them with a thicker stand of turf, not fight the worms.
Build a Thicker Lawn (the long-game answer)
Dense, healthy turf hides casting bumps almost completely. If you can see castings without pushing the grass aside, your lawn isn’t dense enough. The fix is consistent feeding and overseeding. Our turf management programs are built around exactly this. Feeding the crown of the grass plant produces rhizomes, and rhizomes are what build a dense, weed-resistant, bump-masking lawn over time.
Overseed When the Lawn Is Thin
If your lawn is thin, overseeding fills in the gaps. Late summer (August 15 to September 15 in our area) is the best window in Maine. Soil temperatures are still warm enough to germinate quickly, and the cooler nights protect young seedlings from heat stress.
Dethatching (optional, with caveats)
A spring dethatching pass can knock down some of the dried castings and pull out winter debris at the same time. You can rent a power rake or use a hand thatch rake. Do this before the lawn fully greens up. After things start growing, dethatching does more damage than good.
What NOT to Do: Don’t Roll the Lawn
Never roll your lawn to flatten the bumps. Rolling compacts the soil, and compacted soil is exactly what your turf roots can’t grow in. You’ll trade a slightly bumpy lawn for a struggling one. The only time we recommend rolling is right after seeding, with a lightweight roller, to press seed into soil contact. That’s it.
The Real Diagnosis Question
Most “bumpy lawn” complaints we get aren’t really about the bumps. They’re about turf density. The bumps are obvious because there isn’t enough grass between them to hide them.
Drawing on 40+ years of diagnosing Maine lawns, the answer is almost always the same: build the turf. Feed it. Overseed it. Treat the soil. Mow it correctly. The bumps stop being noticeable when the lawn is thick enough to mask them.
If you’re already on one of our programs and your turf isn’t where you want it, give us a call at 207-989-1433. We’ll come walk the property and tell you what your lawn or soil actually needs. If you’re not yet a customer, request a free quote and we’ll come take a look.
Jeremy & the Green Thumb Team