Skip to main content
Over the Garden Fence

Ideal timing for sowing lawn seed

Lawns have come through this summer surprisingly well, especially with all the heat we have had. My unofficial count says we have had at least 15 days of 90 degree heat this summer, and some for several days in row. However, we also had good rains.

For yards that need to be re-seeded, the best window for our area is from the middle of August through the first week in September. (This may need to be adjusted for other parts of Illinois).

If the lawn has had fungal disease this summer, be sure to replace those susceptible lawn grasses with newer varieties that have a higher level of disease resistance genetically. The most popular grasses for in northern Illinois are those that favor cooler, moist soils, like the conditions we have every spring and fall. Kentucky bluegrass and perennial rye are common for full sun locations. Shady areas usually contain fine fescues because they are shade tolerant, however, they do not stand up to traffic.

To further your lawn’s ability to resist diseases, sow in some diversity. There are several varieties of any kind of grass you want, so choose some of each. For example, sow at least three different varieties of a disease resistant bluegrass. Sowing seed of three of more varieties of the same type of grass is called a blend. Or if you decide to go with a combination of bluegrass and ryegrass, this is called a mix. To be even more successful, purchase a seed blend or mix that states a high germination percentage, low weed seed percentages, and inert matter count.

Create a better seedbed by using a hard rake to break up the soil, giving the new seed something to immediately grow into. Putting down a topdressing of black dirt or a mix of black dirt and some other organic matter is another way to prepare the planting area.

Once the seed is down, you can start the germination process with frequent, light watering. Between the watering and natural rainfall, germination should occur in as little as five days for rygrasses or up to 10 to 14 days for bluegrasses. Be consistent in your watering for best results.

Another option is using a slit seeder to place the seed through the existing lawn (dead or alive) and any thatch layer, into the soil about one quarter of an inch. These machines are self-propelled and have a series of vertical disks to cut into the soil. Immediately behind the disks are tubes that carry the seed into the ground. Additionally, there may be a series of rollers to press the newly created slit closed. It is best to run the machine in two different directions to be sure seed is evenly distributed. While the seed could be considered “safer” in the soil through this method, watering is still needed to begin the germination process.

Mowing should begin as soon as the new grass is tall enough to mow. This will help the new grasses send tillers or rhizomes to thicken up. Ideally, your lawn will have been mowed several times before the bad weather sets in.

About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.