Having a bumpy, uneven lawn can be frustrating. It affects the appearance of your yard and can make mowing or playing on the lawn difficult. There are several potential causes for a bumpy lawn and a variety of solutions to help fix it and restore a smooth, even surface.
What causes a bumpy lawn?
There are a few common culprits that can lead to an uneven, bumpy lawn:
- Compacted soil – When soil becomes compressed, water and air can’t penetrate well. This causes an inconsistent growing environment leading to bumps.
- Thatch buildup – An excessive accumulation of dead grass stems and roots. Thatch prevents water and nutrients from reaching the soil.
- Uneven ground – Low spots and depressions in the underlying ground can cause bumps in the overlaying lawn.
- Burrowing pests – Moles, gophers, and other burrowing critters can create mounds and tunnels that disrupt the lawn.
- Heavy equipment – Damage from lawnmowers, tractors, or other heavy machinery crossing the lawn can leave ruts and depressions.
Identifying the specific cause of the bumps is the first step toward fixing them. Compaction, thatch buildup, and pest damage are common causes that can often be addressed without completely regrading and reseeding the lawn.
How to fix soil compaction
Compacted soil prevents air and water from permeating through the soil profile. This leads to uneven growth and bumpy areas. Fixing soil compaction involves mechanical aeration or correcting improper watering and fertilization practices.
Core aeration
Core aeration involves punching small holes into the soil using an aerator machine. This can be rented from most home improvement stores. The holes allow better air and water movement into the soil. For best results:
- Aerate when the lawn is actively growing in early fall or spring.
- Set the aerator to extract soil cores or “plugs” 2-3 inches deep.
- Space the holes 2-3 inches apart across the lawn.
- Go over the lawn in different directions to cover it thoroughly.
- Leave soil plugs on the lawn to break down and add organic matter.
- Water deeply after aerating to fill the holes and further improve soil structure.
Annual core aeration in spring and fall helps alleviate soil compaction for a healthier, smoother lawn.
Improving soil structure
In addition to aeration, adding organic materials like compost can help loosen compacted soil. An application of 1/4 to 1/2 inch of compost worked into the soil in early spring or fall will improve moisture retention, aeration, and the lawn’s ability to root deeply.
Occasional topdressing with a thin layer of compost or quality topsoil will also improve soil structure over time without burying the existing grass.
Correcting improper watering
Overwatering causes tiny soil particles to bind together into a tight mass. Underwatering leads to a very dry and compact soil. Adjust irrigation practices to provide adequate moisture without oversaturating the soil. Water deeply but infrequently, only as needed based on soil and weather conditions. Allow the soil to partially dry out between waterings.
Dealing with excessive thatch
Thatch is a tightly intermingled layer of living and dead grass stems and roots that accumulates between the soil and green foliage. A half-inch of thatch is normal, but deeper layers prevent water and fertilizer from reaching the soil and roots. Thatch buildup causes bumps, brown patches, and other problems. Here’s how to handle excess thatch:
Power raking
Power raking, or vertical mowing, uses stiff tines to remove some of the thatch layer. This can be done in early fall when grass begins going dormant or early spring once dormancy breaks. Set the tines just deep enough to extract accumulated thatch without damaging the crowns of the grass plants. Several passes in different directions may be needed to adequately de-thatch.
Core aeration
The same core aeration described for compaction relief will also gradually thin out excess thatch. The removed soil cores carry bits of thatch with them leaving openings for improved air and water circulation down to the soil.
Topdressing
Applying a thin layer of compost or topsoil over the lawn on a regular basis will help decompose thatch while adding nutrients to the soil.
Adjusting mowing and fertilization
Letting the grass grow slightly taller and avoiding excessive nitrogen fertilization will help reduce thatch building up. Consider switching to a slow-release organic fertilizer applied at moderate rates.
Dethatching products
Special dethatching compounds containing bacteria, enzymes, and surfactants can help break down excess thatch and are applied like other liquid lawn fertilizers. Results may take several applications over a growing season or more.
Dealing with uneven ground
Sometimes the basic shape of the underlying soil is bumpy or uneven. This can only be fully corrected by major grading or adding soil and reseeding. But less intensive options can help in some cases.
Spot topdressing
Identify specific bumps, depressions, or uneven areas and apply a layer of quality topsoil or compost blend just to those spots. Blend edges into the surrounding lawn. Spot seeding or sodding may be needed after topdressing.
Rolling
Using a weighted lawn roller in early spring while the ground is still slightly soft can help flatten down small dips, rises, and bumps in an otherwise flat lawn. Go over low spots several times to flatten them out more. But take care not to compress good areas in the process.
Gradual topdressing
Applying light layers of compost or topsoil across the entire lawn once or twice per year will gradually build up low areas while helping improve soil and drainage. This takes time but can smooth out minor bumps without radical regrading.
Getting rid of burrowing pests
Tunneling moles, gophers, voles, ground squirrels and other burrowing critters can disrupt lawn smoothness. Getting rid of them and leveling out the remaining tunnels and mounds will be needed for an even surface.
Identify the pest
Determine what type of animals are causing damage based on the appearance of tunnels and mounds. Trapping may be needed for definite identification. Correct identification is key for proper removal and control.
Remove the animals
For moles, gophers, and other major tunneling pests, trapping and removal is typically needed. Baiting with toxic baits or fumigation of tunnels are other options in difficult cases. Focus control efforts especially in the spring and fall when populations are more active.
Level out mounds
Use a flat shovel to carefully knock down and spread out any remaining mole hills and gopher mounds. Lightly rake to further blend. Reseed any significant bare or damaged areas.
Establish pest deterrents
Installing physical barriers like wire mesh or netting can help keep burrowing pests out of a lawn after initial removal. Use predator urine granules or vibrational stakes to scare them away.
Fill in holes and tunnels
Fill larger holes or sinking tunnels by carefully lifting the sod, filling the holes with soil, then firmly replacing the sod. Spot seed to blend repairs.
Fixing lawn tractor ruts and depressions
Ruts or depressions left by riding mowers, tractors, or other utility vehicles can become unsightly bumps and dips. They should be leveled and repaired to restore an even lawn surface.
Backfill ruts
Use a stiff rake or shovel to backfill any holes and trenches caused by excessive wheeled traffic when the ground was too soft. Break up compacted soil on the bottom and fill with loosened soil or a 50/50 mix of soil and compost.
Hand tamp repairs
Lightly tamp soil-filled ruts using a hand tamper, roller, or flat board to compact backfill without excessive pressure. Water well to settle the soil.
Seed or sod patched areas
Once filled and leveled, eroded or bare areas in the rut lines will need reseeding or sodding to match the existing grass. Choose the same grass type for best results.
Improve drainage
Adding a layer of compost or gravel in low, wet areas crossed by equipment can improve soil structure and drainage. Reduce compaction by using boards under tires when working in soft areas.
Overseeding worn or bumpy lawn areas
Areas of a lawn that receive excessive wear and traffic or are plagued by ongoing issues often become eyesores with a bumpy, uneven surface. Overseeding can help restore a smooth appearance.
Mow short before overseeding
For the new grass seed to take, cut the lawn very short prior to overseeding. For cool-season grasses like bluegrass or fescue, mow below 2 inches.
Aerate before overseeding
Core aerate two to four weeks before overseeding. This will open up the soil and provide spaces for new grass seeds to take root.
Apply starter fertilizer
Use a starter fertilizer specifically formulated to aid seed germination and establishment. Apply according to label directions within a week before seeding.
Spread grass seed liberally
Use a drop spreader or rotary seeder to spread high quality grass seed over the lawn at the recommended rate. Apply in different directions for even coverage. For high-traffic areas, consider using a mix formulated for durability.
Work seed into soil surface
Use a leaf rake to lightly rake over seeded areas to work some seed into the top 1/8 to 1/4 inch of soil where it can take root.
Water frequently
Keep newly seeded areas consistently moist until the new grass is about 3 inches tall. Water lightly several times per day to keep soil moisture high but avoid runoff.
Let new grass thicken up
Hold off mowing until the new grass is 3-4 inches tall. After that, mow at 2 to 3 inches tall until the grass is well established. Avoid heavy traffic on newly seeded areas.
Complete lawn renovation
In cases of extremely poor, bumpy lawns with multiple issues, a full renovation may be needed. This involves killing the existing lawn, amending soil, grading, and reseeding or sodding for an even surface.
Kill existing grass
Use a non-selective herbicide like glyphosate (Roundup) to kill off existing grass and weeds. It may take several applications spaced a week or two apart to fully kill the lawn.
Add soil amendments
Once dead, break up the top few inches of soil using a rototiller. Mix in 1 to 2 inches of compost and other amendments like lime or peat moss over the lawn to enrich soil quality.
Grade and level the soil
Use a garden rake and shovel to carefully grade and contour the underlying soil to an evenly flat surface. Fill low spots and depressions. Remove buildups and break up compaction.
Seed or sod new lawn
Install new grass seed or sod over the newly prepared lawn bed for improved smoothness, drainage and appearance. Water thoroughly for establishment.
Conclusion
Bumpy, uneven lawns occur due to soil compaction, thatch buildup, settling, pest damage, equipment ruts, or general wear. Fixing the specific underlying problem is key before smoothing and reseeding areas. For widespread issues, core aeration, topdressing, overseeding, or full renovation may be needed. With proper diagnosis and care, bumps can be remedied for a consistently flat, smooth lawn.