The Best Grass for Overseeding in Autumn
For most transition zone and northern lawns‚ Tennessee Fescue Blends or Kentucky Bluegrass blends are the best fall overseeding options․ They germinate well in cool soil‚ tolerate warm days and cold nights‚ and root well before shutting down in winter dormancy․ If you live anywhere in the upper Southeast (Tennessee and north)‚ the safest fall overseeding choice is normally a blend of turf-type tall fescues․ However‚ it really depends on the grass you have in your yard and how much shade your yard gets․
And finally‚ we’ll discuss the advantages of seeding in the fall‚ and how to choose the right grass seed for your lawn․
Why September Through Mid-October Is the Real Window
The temperature of the soil is more important than the date; grass seed germinates best at temperatures between 50 and 65 degrees Fahrenheit․ In Tennessee‚ these temperatures generally fall between mid-September and the third week of October․ If planted too early‚ hot weather can bake the seedlings before they are rooted․ But if you plant too late‚ a hard freeze could destroy the young grass before it has had six to eight weeks․
These plants need six to eight weeks to develop roots enough to withstand freezing temperatures․ To determine when you should be plant‚ count backward from your area’s average date of first hard frost․ In Middle Tennessee‚ that date is the first to second week of November‚ so the recommended planting time is early to mid-September․
There are other reasons for the job besides fall beating spring‚ however․
Soil retains heat from summer longer than does the air‚ and the roots grow when the tops slow down‚ so root mass has more time to establish․ Plus‚ there are fewer weeds than there are in the spring․ Crabgrass and other annual weeds germinate at the same time as your new seed in early spring․ The dew in September and October seems more reliable․ The soil stays moist longer without having to run the sprinkler․
What To Actually Plant‚ Region by Region
Another complication is that Tennessee is in what agronomists call the transition zone․ The summers can be too hot for cool-weather grasses to thrive‚ yet the winters can be too cold for warm-weather grasses to stay green year-round․ In other words‚ if you’re a homeowner in Tennessee‚ you’re in a tough situation‚ and that’s something that a lot of general lawn guides gloss over․
If you have fescue or bluegrass for a lawn (most common in Middle and East Tennessee)‚ overseed with a mixture of turf-type tall fescue․ Newer fescue cultivars have a finer-bladed texture than older K-31 pasture varieties‚ and maintain good color during winter․ These blends should contain at least two or three fescue cultivars‚ so that genetically different plants will handle disease and drought differently across the lawn․
If you want faster green cover‚ incorporate perennial ryegrass․ It should not exceed 10 to 15 percent of the seed mix․ Because its germination time is five to seven days (versus 10 to 14 for fescue)‚ it greens up a week sooner․ If you exceed this percentage‚ the ryegrass will outcompete your fescue seedlings for space due to its faster germination and growth․
On the shady side under oaks and maples common to many Tennessee neighborhoods‚ fine fescue varieties like creeping red fescue or chewings fescue do well when bluegrass and ryegrass fail to grow due to low light․ TN Nursery has shade fescue mixes for conditions where dappled light under mature hardwoods keeps standard lawn grass thin no matter how much seed you throw down․
If you live in West Tennessee or have Bermuda or Zoysia‚ do not overseed cool-season turf types in the fall unless you want a green winter lawn throughout dormancy․ Depending on how soon you want color‚ overseed with annual ryegrass in late September or early October․ Warm-season grass will green up on its own in the lawn by late spring․ This is why seeding permanent cool-season grass into a warm-season lawn in hopes of a permanent transition by summer results in a confused‚ patchy blend of the two types‚ neither dominating․
Getting the Ground Ready Actually Matters More Than the Seed
Much overseeding failure has nothing to do with seed quality or viability․ It is brought on simply because the seed never gets to the soil․ Mow the existing grass lower than normal (1․5 to 2 inches)‚ which will also help to prepare the lawn for overseeding‚ and then bag the clippings immediately․
If the thatch layer exceeds half an inch in thickness‚ dethatch or core aerate the lawn․ A core aerator may leave holes in the soil when it removes plugs from the soil․ A lawn that has not been aerated in over 3 years will require dethatching or aeration․ Some of the seed falls onto decaying grass and thatch‚ but the aerator does push some seed into the holes‚ where they can make contact with soil․
After applying the recommended seed amount (4-6 pounds per 1000 square feet for fescue blends) and straw mulching (also recommended for new grass)‚ it is recommended to apply starter fertilizer with phosphorus (stimulates root growth) and water lightly & often (i․e․‚ 2 - 10 minute sessions per day as opposed to 1 - 30 minute session) for the first 2 weeks‚ until turf is about 3 inches high and ready to mow․ Once completed‚ begin watering and mowing as necessary‚ keeping mower blades sharp so that the grass is being cut rather than torn‚ which can stress new grass seedlings․
What Realistic Timelines Look Like
Do not expect a thick lawn by Thanksgiving․ Although germination can take between one and three weeks‚ depending on the grass‚ and full establishment‚ once your lawn can withstand regular traffic and appear fully thick‚ can take anywhere from eight to 12 weeks․ In Tennessee‚ that generally means that an overseeded lawn will not reach its full potential until late fall‚ followed by the next spring when the turf had a winter season of root growth․
So you can expect even germination in late September‚ good coverage in mid-October‚ and first light mowing in three to four weeks after germination if you started seeding relatively early in September․ After you patiently survive your first winter‚ lawns that were overseeded the previous fall usually look thicker and greener in the spring than those that weren’t overseeded․
Choosing the right seed‚ based on your actual light conditions and the existing type of grass (and not just the cheapest or prettiest one at your neighborhood hardware store) is the difference between a lawn that fills in evenly and a patchwork quilt of textures and colors next summer․
