For best results, seed lawn in September
Ward Upham knows the key to a successful lawn in June-July-August often lies in what happens in September.
“Tall fescue lawns that have become thin over the summer can be thickened up by overseeding in September,” Upham said, a horticulture expert at Kansas State University.
Boosting the lawn, however, is a bit more involved than simply spreading lawn seed across the yard. Upham said the keys to successful lawn seeding are using the proper rates, even dispersal, good seed-to-soil contact and proper watering.
Use the proper rate
For tall fescue lawns, Upham suggests using six to eight pounds of seed per 1,000 square feet for newly-planted areas, and about half that amount for overseeding areas in the shade.
For the other common Kansas variety – Kentucky bluegrass, a smaller seed – use two to three pounds of seed per 1,000 square feet, again half the amount in shady areas.
Using too much seed, he added, makes the lawn more prone to disease and damage from stress. Using too little seed may result in clumpy turf that is not as visually pleasing.
Spread seed evenly
Upham said spreading the seed evenly is best achieved by carefully calibrating the seeder, or by adjusting the seeder to a low setting and making several passes to ensure even distribution.
“Seeding a little on the heavy side with close overlapping is better than missing areas altogether, especially for the bunch-type tall fescue, which does not spread,” he said. “Multiple passes with the seeder in opposite directions should help to avoid this problem.”
Good seed-to-soil contact is essential for good germination rates. Before seeding, mow the grass short (one to one and a half inches) and remove the clippings to increase the amount of light that will reach the young seedlings.
“Normally, we want 1/4 inch of thatch or less when overseeding,” Upham said. “If the thatch layer is 3/4 inch or more, it is usually easiest to use a sod cutter to remove it and start over with a new lawn. You can use a power rake to reduce a thatch layer that is less than 3/4 inch but more than 1/4 inch.”
Upham suggests using a slit seeder, which drops seed directly behind the blade that slices a furrow into the soil.
“The same result can be achieved by using a verticut before broadcasting the seed, and then verticutting in a different direction a second time,” he said.
Core aerators also can be used to seed grass. Go over an area at least three times in different directions before broadcasting the seed. The aerator punches holes in the soil and deposits the cores on the surface of the ground. Germination occurs in the aeration holes.
Water newly-planted areas lightly, but often, keeping soil moist but not waterlogged.
“During hot days, a new lawn may need to be watered three times a day,” Upham said. “If it is watered less, germination will be slowed.”
If days are cool and winds are low, the lawn may only need water every two days.
As the grass plants come up, Upham suggests gradually backing off watering, eventually to just once a week if there is no rain.
“Let the plants tell you when to water,” he said. “If you can push the blades down and they don’t spring back up quickly, the lawn needs water.”
Once the seeds sprout, minimize foot traffic until the seedlings are more robust and ready to be mowed – about three to four inches tall.
When should I fertilize my lawn?
The two most popular grasses grown in Kansas – tall fescue and Kentucky bluegrass – are entering their fall growth cycle as days shorten and temperatures cool at night.
“Cool-season grasses naturally thicken in the fall by tillering (forming new shoots at the base of existing plants) and, for bluegrass, by spreading rhizomes underground,” Upham said.
For those reasons, September is the most important time to fertilize these grasses. Upham suggests applying one to one and a half pounds of actual nitrogen per 1,000 square feet.
“We recommend a quick-release source of nitrogen,” he said. “Most fertilizers sold in garden centers and department stores contain either quick-release nitrogen or a mixture of quick- and slow-release.”
The second most important time to fertilize cool-season grasses is November, Upham said. Doing so will help grass green up earlier next spring and provide nutrients needed until summer. In November, apply a quick-release fertilizer at 1 pound per 1,000 square feet.