Overseeding a lawn requires preparation to ensure success. While choosing the right seed is important, preparing the seedbed is crucial for achieving a lush result. The most important first step is addressing the existing grass, which answers the question of whether you should mow before seeding.
The Immediate Answer: Why Mowing Low is Essential
The answer to whether you should mow before seeding is yes; cut the grass significantly shorter than normal. This low cut maximizes light penetration and achieves better seed-to-soil contact. For most turf varieties, the ideal height before seeding is between 1.5 and 2 inches (38 to 50 millimeters), often the lowest setting on a standard residential mower.
Shorter grass blades ensure that newly germinating seeds receive the necessary sunlight for photosynthesis. Tall existing grass creates a dense canopy that shades the soil surface, starving new seedlings of the light they need to grow strong roots. The reduction in canopy height also facilitates seed-to-soil contact, which is the most significant factor in germination success.
Seeds resting on top of existing grass blades, thatch, or debris are unlikely to germinate because they cannot anchor roots or consistently absorb moisture. Cutting the grass low exposes more bare soil, allowing seeds to fall directly onto the mineral surface. Removing the clippings after this low mow is also helpful, as leaving them creates an additional layer of organic matter that traps seeds above the soil line.
Beyond the Mow: Essential Soil Preparation Steps
Once the lawn is cut short, physical manipulation of the soil surface must begin before seeding. This involves breaking up physical barriers that prevent seeds from reaching the soil. Thatch, which is dead organic material accumulating between the grass and the soil, acts as a shield, preventing water and nutrients from reaching the roots.
Using a dethatching rake or a power rake to remove this material is recommended if the layer is thicker than a quarter-inch. Following up with core aeration significantly improves the seedbed environment. Core aeration involves mechanically pulling small plugs of soil from the ground, which relieves soil compaction and creates open pockets that are perfect receptacles for the new grass seeds.
The holes left by a core aerator allow air, water, and nutrients to penetrate deep into the root zone of the existing turf and new seedlings. This is the ideal time to make necessary soil amendments, such as adjusting the pH with lime or sulfur after a soil test. Applying a starter fertilizer rich in phosphorus immediately after seeding is beneficial, as this nutrient specifically aids in the early development of strong root systems.
The New Lawn Schedule: Mowing After Seeding
After the seed has been spread and initial watering begun, the next step is knowing when to safely introduce the mower. Mowing too soon can dislodge delicate, shallowly rooted seedlings, leading to bare patches. Generally, the first mow should be delayed until the new grass seedlings have reached a height of about 3 to 4 inches (7.5 to 10 centimeters).
Depending on the grass type and growing conditions, this waiting period lasts between four and six weeks after seeding. When the first mow is performed, use a mower with a sharp blade to ensure a clean cut, rather than tearing the tender new growth. Tearing the blades stresses the plant and makes it vulnerable to disease.
The technique for the first few cuts should adhere to the “one-third rule,” meaning never remove more than one-third of the grass blade height at any time. To protect the fragile root structure, the mower deck should be set to its highest possible setting for the first few passes. This high cut promotes root consolidation and helps the new turf mature into a dense, established lawn.