The process of introducing new grass seed, whether through overseeding or starting a new lawn, requires thorough preparation for successful establishment. Cutting the existing grass before seeding is a definitive step that creates the optimal environment for new seeds to thrive.
Why Lowering the Mower Blade is Essential
Cutting the existing grass significantly shorter than its normal height is a mandatory first step before spreading new seed. This action opens the turf canopy, the dense layer of grass blades that normally shades the soil surface. Reducing the height eliminates a physical barrier, allowing the seeds to fall through and make contact with the soil.
The recommended height for this pre-seeding cut is typically between 1.5 and 2 inches. This low cut also allows sunlight and water to penetrate directly to the soil where the seeds will rest. New grass seedlings require consistent moisture and light energy for germination, which is inhibited by the shade of a tall lawn. After cutting, bag or rake up all the clippings to ensure the seedbed is clear of debris.
Key Steps for Soil Readiness
Once the existing turf is cut low and the debris is removed, the next phase focuses on improving soil structure to welcome the new seeds. Achieving maximum seed-to-soil contact is the most important factor for successful germination, ensuring the seed is surrounded by moisture and nutrients. Two mechanical processes, dethatching and aeration, are highly recommended.
Dethatching
Dethatching involves removing the layer of dead and living organic matter, called thatch, that accumulates between the grass blades and the soil surface. A thick thatch layer, more than a half-inch deep, acts like a sponge, preventing seeds from reaching the mineral soil below. Removing this dense mat with a dethatcher or power rake exposes the soil, allowing seeds to embed directly into the ground.
Aeration
Aeration is the process of pulling small plugs or cores of soil from the lawn, which immediately relieves soil compaction. Compacted soil hinders root growth, restricts water movement, and limits the exchange of gases. The holes created by core aeration serve as perfect pockets for the grass seeds to settle into, providing excellent contact with the loosened soil. Applying a starter fertilizer after these steps is beneficial because it contains higher levels of phosphorus, a nutrient that promotes vigorous root development in young seedlings.
Watering and Mowing After Seeding
The first few weeks after seeding are dedicated to careful moisture management to encourage germination. New seeds must be kept consistently moist, but not saturated, which typically requires frequent, light watering sessions. During the germination period, which can last from one to three weeks, the top inch of soil should remain damp, often necessitating two to four short waterings per day.
As the seedlings emerge, the watering strategy shifts from frequent, light applications to less frequent, deeper soakings. This change encourages the new grass roots to grow downward into the soil profile instead of remaining near the surface.
The first mow of the newly seeded area should not occur until the new seedlings have grown to a height of approximately three to four inches. Mowing too early can damage the fragile new plants and pull them from the ground. When the time comes, a sharp mower blade is essential to ensure a clean cut that minimizes stress on the grass. Never remove more than one-third of the grass blade height during any single mowing, even on the first cut, to allow the new turf to continue photosynthesizing efficiently.