University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

Now Is the Time for Overseeding

August 26, 1999

Thinking about overseeding your lawn? Considering planting a new lawn area or totally replacing an existing one? Now is the time.

Even though thoughts of lawn seeding often focus on spring, right now is actually the best time. Soils are warm, so seeds germinate rapidly. Weed problems, principally crabgrass, are less concern as we move into fall. Cooler weather favors rapid development of grasses with little stress. The main thing that could be missing is rainfall, so be sure to have an irrigation plan if rain is sparse.

When overseeding or repairing a lawn area, it is critical to have good seed to soil contact. If seed is just scattered over living grass and debris, little will germinate and grow. The site needs some preparation to assure overseeding success.

If replacing an entire lawn, existing debris can be tilled under or removed. If existing grass or weeds exist, either pull them out or treat with the herbicide glyphosate (Roundup, Kleeraway). Glyphosate may take 10 to 14 days to kill the vegetation, so apply as soon as possible to get the lawn seeded in time.

Overseeding existing lawn areas can be more difficult. One way to achieve good results is to use a slit-seeder that will plant seed through existing grass and debris right into the soil. Vertical mowers, or dethatchers, could also be used, but keep in mind they can be destructive to existing grass. After using these machines, rake away debris and overseed the area.

In the process of overseeding, minor corrections in surface levels can also be done. For example, small depressions can be filled in with quality soil. The lawn could also be core aerated prior to adding soil. If replacing an entire lawn area, be sure to thoroughly amend problem soil, such as clay, with organic matter or quality loam soil.

Finally, be sure to overseed with the right grass. If overseeding into an existing lawn, match the mix with the species present. Adding quality cultivars can help increase stress tolerances. When replacing lawn, match the grass to the site factors. Kentucky bluegrass, often mixed with perennial ryegrass, is best for full sun. When shade influences the site, fine fescues become the preferred species, often mixed with shade tolerant Kentucky bluegrass cultivars.


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