Now is prime time to establish a lawn from seed. Iowa State University Extension and Outreach horticulturists offer tips on selecting seed and planting a new lawn, as well as overseeding an existing lawn. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or firstname.lastname@example.org.
Late summer (mid-August to mid-September) is the best time to establish a lawn from seed in Iowa. Late summer seeding has several advantages over spring seeding. The seeds of cool-season grasses germinate quickly in the warm soil of late summer. Once the seeds germinate, the warm days and cool nights of early fall promote rapid turfgrass growth. The growing grass also has less competition from weeds, as few weed seeds germinate in fall.
When purchasing grass seed, select a high quality seed mix that is best adapted to the site. Kentucky bluegrass is the best choice for sunny areas that receive at least six hours of direct sun each day. Choose a seed mix that contains at least two or three bluegrass cultivars. Because Kentucky bluegrass is slow to establish from seed, perennial ryegrass often is included in bluegrass mixes to speed establishment. (The percentage of perennial ryegrass in a high quality bluegrass mix is generally 20 percent or less.) The fine-leaf fescues (creeping red fescue, hard fescue, chewings fescue, etc.) are the best grasses for shady locations. In lawns that contain sun and shade, select a seed mix that is approximately 60 percent Kentucky bluegrass, 30 percent fine-leaf fescue and 10 percent perennial ryegrass. Kentucky bluegrass will be the dominant grass in the sunny areas, while the fine-leaf fescues will thrive in the shaded portions of the lawn.
The first step in planting a new lawn is establishing the rough grade. Remove construction debris, then fill in low spots and level off high areas. The ground should slope away from the foundation of the house, drive and sidewalks. The rough grading should be done well in advance of seeding to allow settling to occur.
At least 6 inches of good soil are needed to establish a lawn. If necessary, bring in additional topsoil or organic matter. Be sure the topsoil or organic matter is weed-free. Incorporate the additions into the top 4 to 6 inches of soil.
To determine soil fertility, conduct a soil test. Apply the recommended fertilizer, then incorporate it into the soil. Where a soil test has not been made, apply 10 pounds of 10-10-10 or similar analysis fertilizer per 1,000 square feet and till it into the soil. The final step in soil preparation is raking the area. This also is the last opportunity to establish the final grade. Immediately prior to seeding, apply a starter lawn fertilizer. A starter fertilizer is high in phosphorus.
To achieve uniform seed distribution, apply the seed with a drop-type seeder. Sow half the seed in one direction. Apply the remaining half at right angles to the first application. After sowing the seed, lightly rake or drag the area. The seed should be covered to a depth of 1/8 to 1/4 inch. Roll the area lightly to ensure good contact between the seed and soil.
To promote seed germination, mulch the area with clean, weed-free straw. Mulching materials help conserve soil moisture. They also prevent soil erosion and crusting of the soil surface. Do not apply too much mulch, because it may smother the emerging seedlings. Approximately 50 percent of the soil should be visible through the straw. One bale should cover approximately 1,000 square feet. Erosion control mats or blankets, available at garden centers and home improvement stores, are excellent options when sowing seed on steep slopes and other erosion-prone areas.
After the ground has been mulched, water the area. Moisten the upper 1 inch of soil. After the initial watering, irrigate the area frequently and lightly. The objective is to keep the seedbed (upper 1 inch of soil) continuously moist. Do not allow the seedbed to dry out during the germination period. It may be necessary to water two or three times on windy, sunny days. When the grass seedlings are 2 inches tall, water less frequently, but more deeply.
To reduce the competition from the established turfgrass, mow the lawn at a height of 1½ to 2 inches. Successful overseeding requires good seed-to-soil contact. Core aerators, vertical mowers and slit seeders can be used to ensure good seed-to-soil contact.
Core aerators are machines with hollow metal tubes or tines. They remove plugs of soil when run over the lawn. To prepare the site, go over the lawn three or four times with the core aerator. When finished, there should be 20 to 40 holes per square foot. Apply the seed with a drop seeder. Afterward, drag the area with a piece of chain link fence or drag mat to break up the soil cores and mix the seed into the soil.
It also is possible to prepare the site with a vertical mower. When run over the lawn, the knife-like blades of the vertical mower slice through the thatch and penetrate into the upper 1/4 to 1/2 inch of soil. One or two passes should be sufficient. Afterwards, remove any dislodged debris from the lawn. Sow grass seed over the lawn with a drop seeder. Work the seed into the soil by again going over the site with the vertical mower.
Large areas also can be overseeded with a slit seeder. A slit seeder makes small grooves in the soil and deposits the seed directly into the slits.
Core aerators, vertical mowers and slit seeders can be rented at garden centers and rental agencies. For those who would rather not do the work themselves, many professional lawn care companies can overseed lawns.
After seeding, keep the seedbed moist with frequent, light applications of water. It’s usually necessary to water at least once or twice a day. Continue to mow the lawn at a height of 1½ to 2 inches. Mow the lawn frequently to reduce the competition from the established turfgrass. When beginning to mow the new seedlings, gradually increase the mowing height over the following weeks. The final mowing height should be 3 to 3½ inches. Approximately six weeks after germination, fertilize the lawn by applying one pound of actual nitrogen per 1,000 square feet.