When to Mow a Lawn After Overseeding

Mowing

• Mow the existing lawn very low prior to overseeding as the established grass will start to compete with new seeds and seedlings for water and nutrients. After the seed has been scattered in the desired area, water once or twice a day to keep soil moist. Keep mowing the lawn frequently at a height of 1 1/2 to 2 inches during seed establishment. Once the seedlings are 1 1/2 to 2 inches tall, gradually raise mowing over several weeks to reach 2 1/2 to 3 inches.

Fertilizer

• Avoid using fertilizer on reseeded lawns until three weeks after overseeding. Using fertilizer at the time of seeding will produce vigorous growth in the already present grass. This will then shade out the seedlings, so it's best to use fertilizer after seedlings are well established. Use a pound of actual nitrogen for every 1,000 square feet of lawn, as suggested by the Iowa State University Extension.

Timing

• The right time for overseeding depends upon the type of grass seed used. This is generally before the peak time of the natural growth pattern of the selected grass. Overseed with cool season grasses in the cooler regions during fall. Use warm season grasses for overseeding in the warmer regions during spring. If you are using a cool season grass for overseeding warm season grass, the right time would be in the fall. This will encourage the new seeds to get established during the dormant period of the warm season grass.

Site Preparation

• After mowing the existing lawn very low, rake all the excess clippings. The layers of clippings on the grass will prevent the seed from blending with the soil. Save the clippings and use as mulch after the overseeding has been done. Rake the cleared lawn again to aerate the soil surface and improve seed and soil contact. In lawns with high compacted soil, it is best to use a power aerator as this will ensure success of new seed establishment. Use two to three times more seed quantity for overseeding as compared to bare soil seeding. Use a roller after seeding to move the seed into the soil.