Yes, you should cut your grass before seeding. The primary purpose of this pre-seeding mow is to maximize seed-to-soil contact, which is the most significant factor in successful germination. Reducing the height of the existing turf ensures the new seeds can reach the soil surface instead of getting suspended in the thatch layer or resting on grass blades. This preparation step immediately improves the conditions for the seeds, giving them the best opportunity to root and establish themselves quickly. This low cut also reduces the shading effect of the older grass.
The Crucial Role of Low Mowing
Mowing the existing lawn down before spreading seed serves two critical biological functions for the new grass. First, it drastically reduces the competition for resources between the established turf and the tender new seedlings. Taller grass blades utilize a disproportionate amount of soil moisture and nutrients, which are then unavailable to the newly germinating seeds. By reducing the leaf surface area of the existing grass, you temporarily slow its growth and decrease its demand for water and fertilizer.
Second, a lower cut increases light penetration to the soil surface, which is necessary for germination and subsequent seedling growth. Grass seedlings require adequate sunlight to begin photosynthesis and thrive, and they can be easily shaded out by a dense, tall canopy of older grass. Low mowing ensures that when the seeds sprout, the existing turf does not immediately block the light they need to grow strong and healthy. This increased light exposure helps the new grass establish a robust root system.
Setting the Specific Cut Height
For most lawns, the ideal cut height immediately before seeding is between 1.5 and 2 inches. This range is usually the lowest or second-lowest setting your standard lawnmower allows without causing damage to the turf’s crown or “scalping” the soil. This height provides a protective layer for the soil while still allowing maximum light and seed-to-soil contact. For cool-season grasses like fescue or bluegrass, this aggressive reduction in height is a temporary measure that sets the stage for the new growth.
It is necessary to collect all grass clippings after this low cut, rather than mulching them back into the lawn. Leaving a thick layer of clippings on the soil surface will smother the newly spread seed, blocking sunlight and reducing the chance of proper soil contact. The existing grass should be maintained at this reduced height until the new seedlings are well-established, which typically takes a few weeks. This practice continues to favor the growth and development of the new, young grass plants.
Essential Soil Preparation Steps
The low mow should be followed by specific soil preparation actions to create the most receptive seedbed. One of the most beneficial steps is core aeration, which involves removing small plugs of soil from the lawn. This process relieves soil compaction, allowing water, air, and nutrients to penetrate the root zone more easily, and it creates small pockets in which the new seeds can nestle. Aeration significantly improves the seed’s environment and encourages deeper root growth once the seedlings emerge.
Dethatching is another highly recommended step, especially if a thick layer of dead organic material, known as thatch, has accumulated above the soil. This layer can prevent seeds from reaching the mineral soil, rendering the seeding effort ineffective. You can use a dethatching rake or a vertical mower to break up and remove this dense mat of debris, ensuring the seeds can make firm contact with the soil underneath.
After aeration and dethatching, lightly raking the surface helps to work the loose soil and seed into the prepared holes and channels. This minor grading action ensures a level surface and maximizes the physical connection between the seed and the soil particles. Removing large debris like rocks or thick clumps of dead grass before spreading the seed provides a clean, even canvas for the most uniform germination and establishment possible.