Even when it’s lush and green, an uneven lawn makes sunbathing and games less enjoyable and makes mowing hard work that leaves ugly bald patches. Drainage problems are also more likely, putting your lawn at risk for disease and your foundation at risk for damage. Nearly every lawn develops lumps and bumps eventually, but regardless of the cause, it’s almost always possible to straighten things out.
Determining the Cause
Knowing why your lawn has developed uneven areas helps you decide how to go about leveling them out. Ground settling during the seasonal freeze and thaw cycle is one of the most common causes of bumps in a lawn. Buried objects, such as logs or construction debris, can leave pits as they settle and decay. Diseased grass can cause the lawn to sink in places. A damaged sprinkler system or leaking pipe can cause underground erosion.
It’s usually possible to correct uneven areas like these with minimal damage to your existing grass. For hills or slopes, however, you might need to regrade the entire lawn.
Smoothing Out Minor Bumps
If the dents in your lawn are less than 1 inch deep, top dressing is a simple way to even them out.
The best top dressing for your lawn depends on your soil type. For sandy or loam soils, use a gritty top dressing such as coarse sand or a mixture of coarse sand, peat or compost, and topsoil. For clay soils, use a mixture of compost and topsoil. Spring and early fall are the best times to do the job because your grass will have plenty of time to grow through the top dressing.
First, prepare your lawn by mowing it with the mower blade at the lowest setting. Dethatch the lawn with a dethatcher or a rake. If the lawn hasn’t been aerated in the last three years, aerate it with a spike aerator or aerating machine.
With a shovel or trowel, apply the top dressing to the lowest point of the depressions in the lawn. Add no more than 1/2 inch of top dressing to avoid burying the grass. Rake the top dressing to even it out over the soil, then use a push broom to work it in further and uncover the grass. Finish by watering the grass to settle the top dressing.
Alternatively, you can fill the depression with soil and reseed the area.
Correcting a Moderately Uneven Lawn
For depressions of between 1 to 24 inches deep, resodding is the most practical approach. This requires cutting out the existing sod, addressing the cause of the sinking, then adding more stable soil.
To remove the sod, water the grass and use a shovel or spade to cut 1-foot squares into the grass below root level. Gently pry up the squares of sod until the roots are released from the soil. If the grass is healthy, roll up the sod grass-side inward and place it in a cool, shady spot to keep it moist. If the grass is in poor condition, you’ll need healthy sod or grass seed to replace it.
Check for anything within the soil that might have caused the sinking, such as a rotten log or leaking sprinkler, and correct the problem. Fill the depression with topsoil and gently tamp it down. If the depression is more than 6 inches deep, fill in several inches at a time, tamping and watering the soil as you go to remove air pockets. The filled area should be around 1 inch higher than the surrounding lawn to allow for settling. Replace the sod or reseed the area, then water thoroughly.
Regrading a Severely Uneven Lawn
Sometimes spot-correcting just isn’t enough. If your lawn has large slopes or deep, wide pits, regrading the whole area is the only way to get an even surface. This will cover your existing grass, so you’ll need to resod or reseed.
Creating a slope that ensures good drainage and easy mowing takes some planning. Your lawn should slope downward away from your house to prevent it from funneling water toward your foundation. A slope of around 6 inches every 10 feet is ideal, but anywhere between 2.5 to 12 inches every 10 feet is acceptable.
If you’re unsure about calculating or creating an optimal slope, it’s worth hiring an experienced landscaper. This is especially true if you have a large lawn. A landscaper can bring in equipment, such as a site level and backhoe, to get the job done quickly and correctly.
First, establish your lawn’s slope by calculating its run and rise. This tells you the difference in height from the high point near the foundation to the low point near the storm sewer or gutter.
Place a stake at the highest and the lowest points of your lawn. Tie a rope between the stakes and hang line levels on the rope to ensure it’s perfectly level. Measure the full length of the rope to find your lawn’s run. Then go to the stake at the lowest point and measure the distance from the rope to the ground. This is the lawn’s rise. If the run is 100 feet long, there should be a rise of between 25 inches to 10 feet.
If the current slope is too low or the lawn slopes toward the house, redistribute the soil to create a better grade and an even surface. Before you start digging, locate any pipes, wires or other objects under your lawn to avoid damaging them.
Start regrading by removing soil from the high spots in the lawn. To create the new grade, you can redistribute the topsoil you removed or add topsoil from another source. First, add 2 inches of topsoil near your foundation and till it into the existing soil to promote good drainage. Then add another 4 to 6 inches of soil, but leave 6 to 8 inches of your foundation visible. Gradually distribute soil until you have the slope you want, then use a landscaping rake to create an even surface.
For a flawless finish, drag the edge of a two-by-four over the soil to smooth out any remaining bumps. When you’re satisfied, lay your sod or reseed the lawn.
A level, correctly graded lawn is not only a lot more enjoyable to use, it’s also easier to maintain and protects your home from water damage. A few shallow low spots are easy enough to correct by top dressing or resodding, but if your lawn is hilly or poorly sloped, it will benefit from a full regrading.