Top Dressing Your Lawn

Low spots in an otherwise level lawn are caused by several factors. Most homeowners would like to get rid of them. Mowing over an uneven terrain can get tiring very quickly, both physically and emotionally.

Depressions in the soil often occur where gas, water and sewer lines are installed. The soil surrounding the pipes doesn't immediately settle, but after a few years, you may find sunken trenches in the lawn once the soil packs down.

Sunken areas are also caused by the decay of old tree stumps, and the result can literally appear overnight. One former client of mine had chopped down a dying American Elm tree on her property and had buried its roots when she first purchased the home. Twenty years later she hired my landscaping firm to completely regrade and reseed her lawn. At the time, we were unaware of the previous removal and the lawn had only minor depressions.

When you put in a new lawn, you must water it extensively for the first few weeks, which we did for her. All was going well until about three weeks after we had started the project when I received a phone call from her early one morning. There was a huge sunken hole where the old tree had been. She was in a panic, wondering what my landscape crew had done to her yard. After some questioning, she remembered removing the old tree. It took twenty years for the roots to decay, but with the consistent watering, the soil around the roots had finally and quickly settled.

Winter freezing and thawing can also create high and rough spots in the lawn. As the water in the soil freezes, it expands. When it melts, the soil doesn't always settle back evenly.

For many years, the traditional method for leveling a lawn was to compress the high areas down to the low spots. This was usually accomplished with large, steel cylinders, filled with concrete or water, which were rolled back and forth across the lawn. This practice is no longer recommended because it squeezes the air space out of the soil into which roots need to grow and breathe.

Today, low spots are removed by top dressing the lawn, which means adding topsoil to the low spots and bringing them up to the same level as the higher grade. Dumping small piles of soil across the yard and raking it out while leaving the grass in place accomplishes this.

Where the new soil depth is less in 1 to 1½ inches, the grass will probably grow back up through the filled area. I do not recommend placing more than three inches of soil on top of grass because it will smother the old and may cause it to decay that could create methane gas that can kill the new grass growing above it.

Instead, in the deeper spots, I suggest splitting open the existing sod and filling in beneath it with soil, then relaying the sod. You could also top dress half the depth this year and the remainder the following year. You can also remove the old grass, add soil and reseed or resod areas or whole lawns.

To determine how much soil you will need, measure the length, width and average depth of the shallows or dips in question. A cubic yard of pulverized and blended topsoil, which is machine processed to clumps no larger that the size of the end of you finger, will cover a 648 square foot area to a depth of half an inch.

Now is the time to get the materials on hand as well as the mindset to begin top dressing the lawn. Functionally do the job between August 15th and September 10th. The days are getting shorter and the nights are getting cooler. These factors will keep the watering responsibilities more manageable and the weed seeds will be less likely to germinate in the Fall. This gives the lawn a better chance to grow back quickly and be mowed 4 or more times and be ready for winter.