Overseeding in fall can repair, improve lawn
Tall fescue still holds the title as the best-adapted cool-season lawn turf for the gamut of central U.S. weather extremes.
Even so, overseeding existing fescue lawns during September is a fairly common practice, according to Chip Miller, horticulturist with Kansas State University Research and Extension.
Typically, some homeowners are hoping to improve their lawn's thickness or fill in bare spots, following a stressful growing season. Others are trying to improve lawn quality by mixing in a new, improved fescue variety with the old standby they've already got--Kentucky 31 or K-31 tall fescue.
They may or may not succeed in improving their lawn, Miller said. Most often, success depends on the seed variety they select and their ability to avoid several serious mistakes.
"For example, K-31 has been around for a long time, and it tends to have the least expensive seed on the market," Miller explained. "But, it grows so fast that it can require mowing more often than any other lawn turf grown in Kansas. It also has a tendency to react to stress by clumping.
"Simply put: K-31 is a cheap workhorse. So, it may still be a good choice for large, open areas that need to look covered, not manicured. For lawns, however, the newer varieties both look and perform better."
Each year, K-State scientists rate tall fescue varieties for color, green up, quality and texture. In their largest Tall Fescue Cultivar Trial near Wichita, they now have 113 different varieties under study. Their most recently reported recommendations included:
Apache III, Avenger, Biltmore, Blackwatch, Cayenne, Coshise III, Dynasty, Escalade, Falcon IV, Fidelity, Finelawn Elite, Forte, Guardian 21, Inferno, Justice, Kalahari, Matador, Padre, Picasso, Regiment II, Rembrandt, 2nd Millennium, Tar Heel, Titanium, Ultimate, Watchdog and Wolfpack.
"You shouldn't try to buy a specific variety, though. For one thing, every member of the trial's top 30 fescues ranked practically alike. For another, no store is going to stock all of those cultivars," Miller said. "So, you need to find a retail nursery or garden center that keeps up with the research for you and offers a local blend of several cultivars. Blends let you take advantage of different varieties' differing strengths."
Planting good seed badly can still yield problems, the horticulturist warned. The seed has to go down evenly and at the recommended rate with good seed-to-soil contact, followed by proper watering. Achieving good seed-to-soil contact typically requires some advance preparation. The thicker the lawn thatch and/or the more compacted the soil, the more important that prep work becomes, Miller said.
"You can do it with a level-head (bow) rake that you use to disturb and even furrow the soil. But I wouldn't suggest doing the job by hand unless you're only overseeding some pretty small bare spots," he said. "Otherwise, your best choices are machines you'll probably need to rent.
"You can use a core aerator--which will make your lawn look littered with little cigar-shaped soil cores for a couple of weeks, but can loosen compacted soil and break through thatch. Or, you can use a power rake, which mostly is designed to cut through and pull up a thatch layer, but can tear up an existing lawn if not handled right. Or, you can try a verticutter that slices through, rather than ripping out thatch, but still needs careful handling."
A cut-through-the-thatch machine that also sows and covers seed--known as a slit seeder--may also be available for rent at some stores, Miller said. As with the other machines, however, it will require upper body strength to operate well. So, some homeowners may want to hire help.
For an existing lawn, the overseeding rate for tall fescue or Kentucky bluegrass is half or less of what's recommended for starting a new lawn from scratch. K-State's recommended full-seeding rate for new tall fescue lawns in the central Plains is 6 to 8 pounds of seed per 1,000 square feet of lawn. For new Kentucky bluegrass lawns, it's 2 to 3 pounds per 1,000 square feet.