So things got busy this fall, and before you know it, frosty nights are fast approaching. Does that mean it’s too late to do anything about that thin, scraggly lawn?
Maybe not.
A few factors can string out fall’s prime grass-seed-planting window and buy you more time than you thought to get grass seed in the ground.
Ideal time to plant grass
Cool Season Grasses
For cool-season grasses (Kentucky bluegrass, perennial ryegrass, fine fescue), the ideal time to seed or overseed a lawn is late summer into early fall. That’s because the soil is still warm, but summer’s intense heat is backing off and the odds of rain go up. Fewer weeds also germinate later in the season, meaning less competition than in spring grass plantings.
An ideal recipe for good grass germination is daytime air temperatures between 60 and 75 degrees and soil temperatures between 50 and 65 degrees. That translates into the generally accepted rule that cool-season grasses are best planted about 45 days before the region’s average first killing-frost date of fall. That allows both for germination and a couple of weeks of frost-free root growth.
In colder parts of the U.S. (Zones 4-5), the ideal fall grass-seeding window falls approximately between Aug. 15 and Sept. 15. In Zone 6, the back end is two weeks later, and in Zone 7, it’s September into mid-October.
For turf-type tall fescue, which is more vulnerable to first-year winter damage when seeded too late in the fall, err toward the early end of those ranges.
Warm Season Grasses
Warm-season grasses (St. Augustine, bermudagrass, Bahia grass) are best seeded in spring to early summer in Zones 8 and up.
Consider these factors when planting grass in the fall
Since fall weather can vary widely from year to year, grass germination runs later in some years than others. This makes it even hard to predict the best time to plant grass.
Soil Temperature
What matters the most is the current season’s weather – and especially the soil temperature. As long as soil temperatures stay above 50 degrees, most cool-season grasses will germinate regardless of what the calendar says.
Soil thermometers are available in garden centers and catalogs to give the most accurate reading.
Weather Forecast
Check the long-range forecast to see if temperatures are expected to run above normal – or at least above frosty levels. That’s been happening more often in recent years as the warming climate has pushed back fall frost-date norms.
Keep in mind, too, that a single brush with frost doesn’t necessarily equate with no chance of germination. Often, days or weeks of warm weather will follow the season’s first frosty night.
Type of grass seed
Different species of grass germinate at different rates, so the type of grass you’re seeding can make a difference in whether it comes up or not before the weather gets too cold.
Perennial ryegrass, for example, germinates in as few as 5 to 10 days, while fine fescues typically germinate in 10 to 14 days. Kentucky bluegrass is the slowest of the main cool-season grasses to germinate at 14 to 30 days.
Turf-type tall fescue is a little more sensitive to soil temperature and germinates best at 60 degrees and up, taking 7 to 21 days to sprout depending on temperature, variety, and soil moisture.
Encourage fast seed germination
Speed up fall grass growth by encouraging the fastest possible germination and new growth.
- Ensure good seed-to-soil contact (i.e. loosening the soil and lightly tamping after seeding)
- Cover the seeded area with a light layer of GreenView Fairway Formula Seeding Success
- Keep the ground consistently damp.
The age, quality, and particular cultivar of the seed also is a factor in how fast the seed germinates.
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