Overseeding involves spreading new grass seed over existing turf to improve density and health. Proper care of new seedlings is essential, especially regarding the first mowing. Cutting the new grass too soon or incorrectly can damage or uproot the tender shoots, undoing the work.
Determining the Right Time for the First Cut
The decision to mow is based on the physical maturity of the new grass, not a specific calendar date. Seedlings must reach a certain height and possess stable root systems before they can withstand the mechanical stress of a mower. Most experts recommend waiting until the new grass blades are between 3 and 4 inches tall before the first cut.
This height indicates the seedlings have developed a robust root structure to anchor themselves firmly. To check stability, gently tug on a few blades; if they resist being pulled out, the roots are likely established. Mowing prematurely, when roots are shallow, risks tearing the plants out of the ground.
The time to reach this stage typically falls within two to four weeks following germination, but this varies widely depending on the grass species. Faster-growing types like ryegrass may be ready sooner, while slower varieties such as Kentucky bluegrass may require four weeks or more. Waiting until the grass blades reach the target height is a more reliable measure than counting the days since seeding.
Essential Mower Setup for Seedlings
Once the new growth is ready, the mower requires careful preparation to ensure a clean, stress-free cut. The most important adjustment is raising the cutting height to the highest setting possible. This ensures the first cut adheres to the “one-third rule,” which dictates removing no more than one-third of the total blade height.
The mower blade must be razor-sharp. A dull blade tears and shreds the tender new grass, leaving ragged edges susceptible to disease and dehydration. A clean, sharp cut allows the plant to heal quickly and continue its normal growth process.
Mow only when the soil is dry enough to prevent the wheels from sinking or tearing up the fragile seedlings. Mowing wet grass leads to clumping and uneven cuts, stressing the new turf. Bagging the clippings for the first cut is often the safest option to prevent them from clumping and smothering the young grass beneath.
Transitioning to a Regular Mowing Schedule
After the initial cut, transition the lawn into a standard maintenance routine to encourage thickening and root development. Subsequent mows should still be performed at the highest deck setting to maintain maximum blade length, which fosters deeper root growth. Taller grass blades allow for greater photosynthesis, supporting the energy demands of the developing root system.
Subsequent cuts typically occur on a weekly basis, or as needed to maintain the height. The one-third rule remains the guiding principle for every cut, ensuring the grass is never severely stressed by removing too much leaf material. This consistent removal promotes lateral growth and tillering, helping the lawn fill in more densely.
If a shorter final height is desired, gradually lower the mower deck over several weeks, never all at once. The cutting height can be lowered by one notch each week until the preferred level is reached, while still observing the one-third rule. Introducing a starter fertilizer with higher phosphorus shortly after the first few mows supports establishment by providing nutrients for root development.