Applying material on top of grass is possible, but calling it “dirt” is inaccurate and can damage the lawn. The correct practice is called topdressing, which involves spreading a thin layer of specialized soil mixture over an existing lawn. When performed correctly using the right materials, topdressing offers significant benefits for turf health and appearance. Using too much material or a heavy, inappropriate soil type can quickly smother the grass blades, blocking sunlight and air, which kills the lawn.
The Purpose of Topdressing Existing Lawns
Homeowners use topdressing to address common issues and improve the overall structure of their turf environment. A primary reason is to level out minor depressions, divots, and uneven areas that develop over time due to settling or environmental factors. By filling these hollows, topdressing creates a smoother, safer surface for mowing and recreation, preventing scalping of the grass blades.
The process also improves soil structure without completely removing the established lawn. Applying a quality topdressing mix can help break up heavy clay soils by introducing larger particles, enhancing aeration and drainage. Conversely, adding organic matter improves the water retention capacity of overly sandy soils, making nutrients more available to the grass roots.
Topdressing is also beneficial when overseeding a lawn to increase turf density. The thin layer creates an ideal seedbed, providing a protective cover and holding moisture around the newly sown grass seeds. This environment encourages quicker germination and establishment compared to scattering seed directly onto the existing, hard soil surface.
Selecting the Right Material for Application
The success of topdressing depends entirely on choosing a specialized mixture, not common garden soil, which is often too heavy. Appropriate materials are typically a blend of sand, loam (a mixture of sand, silt, and clay), and organic matter like compost. Using a material that closely matches the texture of the existing soil is important to prevent the formation of distinct layers that impede drainage.
High-quality, screened compost is a recommended component because it introduces beneficial microorganisms and organic carbon into the root zone. This organic matter helps bind soil particles, improving the soil’s ability to hold water and nutrients while stimulating the natural breakdown of the thatch layer. Sand is often included to improve drainage, especially in heavy clay areas, but it must be a coarse, lime-free variety, as fine sand can compact and worsen drainage.
It is necessary to avoid materials like heavy clay, unscreened topsoil, or pure peat moss. Common topsoil often contains weed seeds and may be too dense. Clay-heavy material can seal the surface, creating an impermeable layer that suffocates the roots. The material must be finely screened to ensure it filters down easily through the existing grass blades to reach the soil surface.
Step-by-Step Guide for Application
Before applying the topdressing material, the lawn should be mowed at a lower-than-normal height to expose more of the soil surface. Aerating the lawn beforehand is highly beneficial because the mixture will settle into the holes, integrating the new material deeper into the root zone. Ensuring the grass is dry before starting allows the material to spread more smoothly and prevents clumping.
The topdressing mixture is typically spread by shoveling small piles across the lawn surface, then distributed evenly using a stiff rake, push broom, or specialized leveling tool. The most important instruction is the strict limitation on application thickness. The material must be applied in a very thin layer, ideally no more than 1/4 inch thick, and never exceeding 1/2 inch.
The goal is to dust the lawn lightly, allowing at least 75% of the grass blades to remain visible and exposed to sunlight and air. A layer that is too thick will effectively smother the turf by blocking photosynthesis, leading to grass death. After spreading, the material should be worked into the base of the grass plants until it settles down to the soil level. A light watering immediately after application helps the material settle further and begins integration with the existing soil.