Why Fill in Lawn Depressions With Topsoil?

Water Movement

• Whenever the lawn is irrigated or rained on, depressions capture and hold water on or near the surface longer. The shallow roots of grass can keep clear of most waterlogged areas, but in depressions the moisture may stick around long enough to become boggy or at least cause fungal root rot to get a foothold in the yard.

Debris

• Water and wind wash debris and other matter into the depression, leaving a mat that can cover the grass there and kill it. If it is a narrow enough depression that the lawn mower cannot reach it, then this area will have to frequently be manually cleaned out and the grass trimmed down, or else it may disguise the depression and make it hazardous.

Hazards

• Depressions with narrow openings, especially those several inches deep, are hazardous to people running or at play. The leaves of the grass grow up enough to disguise the hole, and lawn mowers don't expose it. There's no visual indication of a hole, and a foot can get caught, twisting ankles and sending people or pets tumbling.

Method

• Topsoil is used to fill lawn depressions because the top 2 to 3 inches of soil has organic matter and life that the lawn needs to live. Filling a shallow hole with topsoil allows the grass to continue growing through it, but deeper depressions are more difficult. They must either be filled an inch at a time, allowing the grass to grow through each time, or the sod must be scraped up at a soil depth of 2 inches, then the depression filled, then the sod laid over the topsoil and watered thoroughly.