Yes, you should mow before seeding your lawn. This preparatory step influences the success of your new grass. The primary goal of this low cut is to manipulate the environment of the existing turf, ensuring maximum seed-to-soil contact and adequate light penetration. Without this preparation, new seedlings face immediate competition from the established grass blades.
Why Mowing is Essential for Seeding Success
Mowing the existing turf significantly lower than usual addresses the physical barrier that prevents seeds from reaching the soil. Grass seeds must absorb moisture from the soil to initiate germination, known as imbibition. If seeds are caught suspended in the thatch layer or on top of long grass blades, they quickly dry out and die.
The established grass canopy also creates a dense shading effect on emerging seedlings. New grass plants rely on direct sunlight for photosynthesis, which fuels their initial growth. Taller, existing blades act as a shade cloth, starving the new sprouts of the solar energy they need. This shading hinders development and encourages a weak, spindly growth habit as the seedlings stretch for light.
Cutting the lawn low opens the turf canopy, allowing seeds to filter down to the soil surface where they can absorb water. This process temporarily reduces the competitive advantage of the mature grass, slowing its growth and minimizing light obstruction. This window of reduced competition allows new seedlings to establish a foothold before the existing turf recovers.
Determining the Correct Mowing Height
The objective of this pre-seeding cut is to achieve a low, open canopy without “scalping” the soil, which risks damaging the turf crown. For most cool-season grasses, such as fescue or bluegrass, the ideal height before seeding is between 1.5 and 2.5 inches. Set your mower to its lowest safe setting, which is often one or two notches lower than your normal maintenance height.
Cutting the grass low is a necessary shock to the established turf. This stress temporarily slows the growth of existing plants, giving the new seed a head start. Use a sharp blade to make a clean cut and reduce tearing, which minimizes stress on the grass plants.
Following the low cut, remove all grass clippings from the lawn surface, either by bagging them immediately or thoroughly raking the area. Leaving a layer of clippings will block the path of the seeds to the soil and impede light penetration for emerging seedlings. A clean, open surface is necessary for the next steps in soil preparation and seed distribution.
Essential Steps Beyond Mowing
Once the grass has been mowed low and clippings are removed, the next steps focus on preparing the soil itself for the seeds. Core aeration, which involves pulling small plugs of soil from the ground, is beneficial. This process relieves soil compaction, a common inhibitor of root growth, and creates thousands of small pockets perfect for receiving seed, water, and nutrients.
If your lawn has a dense layer of thatch—dead and decaying organic matter—you may need to dethatch or scarify the area. Thatch acts like a sponge, holding the seed above the soil and preventing seed-to-soil contact. If the thatch layer exceeds half an inch in thickness, mechanical removal is necessary to expose the mineral soil surface for successful germination.
Before spreading the seed, address the soil’s nutritional profile. Applying a starter fertilizer, typically high in phosphorus (the middle number in the N-P-K ratio), provides the specific nutrients needed for robust root development in young seedlings. Also, perform a simple soil test to check the pH level. If the soil is too acidic, applying an amendment like pulverized lime before seeding adjusts the pH to a more neutral range, ensuring the new grass absorbs nutrients efficiently.