One call we get a lot of in the Spring is “My lawn is really bumpy and uneven. Can you roll my lawn for me?” On the heavy clay soil we have in the GTA, nothing short of a steamroller can exert enough pressure to flatten a lawn by force. And if you did manage it, the soil would be so compact it would choke your grass to death anyway.
If part of the lawn sinks and creates a depression the first thing to do is determine why. Removing the cause before correcting the effect is crucial. For any depression an inch or more deep, repair should involve removing the sod, correcting the cause of the sinking, and then back filling with new soil with enough extra to allow for settling. The removed sod can be put back in place if it is still in good shape, or replaced with new sod or seed. A shallow depression in the lawn – less than an inch deep – can be corrected gradually by sprinkling top dressing over it. Compost based mixes are good for this.
A very common problem is that people often perceive a lawn is bumpy when it has nothing to do with soil! The lawn is made up of layers, for simplicity, lets say: the soil, roots, thatch, and the blades. Thatch is the area just above the soil, that protects the roots. It is normally about 1/4″-1″ in height of matted decomposing grass clippings and generally dying old grass plants that fade away as new plants are generated. When you have a thin lawn or a disease or insect problem that is weakening an area (think Chinch bugs), the blades go first, then the thatch rapidly decomposes leaving bare soil. This bare area then erodes even deeper with rainfall, wind and activity. That leaves a depression when compared to the surrounding area of healthy lawn. This is what we describe as the illusion of a bump. Multiply that by several areas and voila! You feel like you have a bumpy lawn!
Bumps and rises also need to be diagnosed before correction. If caused by an object, it will need to be removed. If a bump is from burrowing animals they will have to be removed before the area can be smoothed. It may be possible to flatten smaller bumps by stepping on them.
The best way to correct and create a lawn that has very few bumps, is really quite simple- Ensure you have a green thick and healthy lawn. Your lawn care program should include high-end nutrition components that thicken and fortify your grass plants, regular aeration to loosen the soil and lessen heaving, overseeeding to thicken the lawn and create a stronger more pest resistant lawn, as well as proactive insect control for Grubs and Chinch bugs.
Spring is the best AND worst time for people worried about lumpy lawn. The ground is soft and grass grows quickly to cover any repairs, but snowmelt-saturated soil plus traffic on your lawn add up to new bumps. You can read more in our April checklist. There are tips to avoiding creating ruts from lawn mower wheels when you mow the lawn in our lawn cutting tips section as well.