The final month of summer is here, meaning children are returning to school and pools will be closing soon. The end of summer also signifies shorter days, cooler temperatures and a nearing finish line for the long marathon run by our cool season lawns. Summer is tough on the fescues, Kentucky bluegrass, and perennial ryegrass with the impacts of drought, heat, insects and disease often opening the door for bare spots and weed encroachment.
The quality of a lawn is most often judged by color, which can be fickle depending on the environment and doesn’t always indicate the long-term sustainability of the sward. Most grasses have a fairly good drought dormancy mechanism, can turn brown for a few weeks and still come back strong in the fall. Density, or the number of desired plants in the yard, is perhaps a more appropriate measure of quality. Plants come from seed, and fortunately for cool season lawns, we have the ability to use that seed to restore the density that may be lost during the summer grind.
Many of our troublesome weeds seed every year, so why wouldn’t we overseed a lawn every few years to restore density? Unless pre-treated, seed is organic, pesticide free, and requires little specialized equipment. Other recommended fall practices, such as aerification, verticutting and fertilization, provide a perfect seedbed and nutritive launchpad for new seedlings. Seeding open areas or even a slightly compromised lawn can also introduce newer, more adapted, cultivars that may have increased stress and pest tolerance. At this late point in the season, instead of devoting inputs into controlling a persistent disease issue, perhaps investing in seeding during the September recovery period is a wiser choice.
A few additional tips for successful fall seeding are below. Another helpful reference article from the Purdue and U of Illinois turfgrass team can be found here – Lawn Improvement Programs: AY-13-W. For more information on home lawn care, see https://turf.purdue.edu/homeowner-publications/.
- Choose seed wisely. Annual ryegrass, commonly seen in a “contractor’s mixture”, is not a good choice since as an annual will not persist. Inspect the seed tag carefully. Turf-type tall fescue is most often suggested for this region, along with Kentucky bluegrass or fine fescue species. If using tall fescue, try to choose younger bags that are more likely to have viable endophytes (symbiotic fungi that improve plant health). For a deeper dive into tested cultivars in this region, see the National Turfgrass Evaluation Program database.
- Consider if weed control is needed prior to overseeding. If using a herbicide, read the label thoroughly and adhere to the post-application reseeding interval or risk injuring your newly planted seedlings.
- Prior to seeding, reduce the mowing height to 1.5 – 2 inches to reduce competition from other grasses. This is the only instance that reducing mowing height to this level on lawns is recommended. Mow low until new seedlings are being cut and return back to 3 – 4 inches.
- Ensure good seed-soil contact with aerification and/or verticutting (a.k.a. power raking).
- Apply seed at appropriate rate (e.g. 6-9 lbs/1000 sq ft for turf-type tall fescue). Split the rate and seed in two directions to ensure good coverage.
- After germination, apply a starter fertilizer at 1.0 lbs of N/1000 sq ft. For assistance with fertilizer calibration, see the Purdue Turfgrass Fertilizer Calculator.
- During the first few weeks, irrigate lightly and frequently. A good adage is to keep the soil dark, but don’t water enough that it floods and glistens.