Overseeding involves planting new grass seed over existing turf to improve density and fill in bare patches. While this practice revitalizes a lawn, its success hinges on the proper care of the delicate new seedlings. Timing the first mow correctly is paramount, as cutting the grass too early risks undoing the effort and investment. Fragile sprouts require time to develop a foundational root system before the mechanical stress of a mower can be introduced.
Conditions for the Initial Safe Mow
The decision to mow should be based on the physical development of the new grass, not merely on the number of days passed since seeding. The true indicator is the height of the new seedlings, which must reach at least three to four inches before the first cut can be safely considered. This height indicates the seedling has invested enough energy into anchoring roots below the soil surface. The new plants must have established a root structure strong enough to withstand the vacuum and cutting action of the mower deck.
The Tug Test
A simple way to test for this maturity is the “tug test,” where you gently pull on a few new grass blades. If the seedlings resist the light tug and remain firmly in the soil, their roots are sufficiently developed to handle the stress of mowing. If the sprouts easily pull out, the root system is too immature, and mowing will likely cause widespread uprooting. Cutting too soon can also damage the growing point of the grass, stunting its ability to photosynthesize and generate energy.
Proper Techniques for the First Cut
When the new grass has met the height and root maturity requirements, the first cut must be executed with extreme care. The most significant rule is to follow the one-third rule, which mandates that you never remove more than one-third of the grass blade height in a single session. Since the grass should be about four inches tall, the mower deck must be set to its highest setting to ensure the cut is light and removes only the top inch or less.
Equipment and Conditions
It is essential to use a mower with an extremely sharp blade to slice cleanly through the new, soft grass blades. A dull blade will tear the tender shoots, creating ragged edges that stress the plant and make it vulnerable to disease. The lawn must be completely dry before beginning, as mowing wet grass can lead to clumping that smothers the new seedlings. Bagging the clippings during this initial cut is often recommended to prevent debris from settling on the young plants.
Resuming the Regular Mowing Schedule
Following the successful first cut, the goal is to transition the lawn to a sustainable maintenance routine without stressing the new growth. For the next few weeks, the mowing frequency may need to be slightly higher than normal to strictly adhere to the one-third rule. Monitor the grass closely and plan to mow again as soon as the blades exceed the desired height by one-third.
Adjusting Height and Fertilization
The height of the lawn should be gradually lowered over several weeks, not all at once. After the first two or three successful cuts, the mower height can be incrementally lowered until the desired permanent height is reached. Introducing chemical treatments, such as weed killers, should be delayed until the new grass has been mowed at least four times. A starter fertilizer, if not applied during seeding, can be safely applied about two to four weeks after germination to provide necessary nutrients.