Overseeding
Overseeding for thin Kansas City lawns
Tall fescue is a bunch grass. It does not run, so thin stays thin until somebody puts seed in it.
Overseeding is available in Missouri and Kansas.
Why a thin fescue lawn stays thin
Bermuda and bluegrass spread sideways on runners and heal their own bare spots. Tall fescue does not. Each plant is a clump holding its own square of ground, so every plant lost to August heat, brown patch, a dog or a drought stays lost. The gap does not close on its own.
That is the trade for growing it here. Kansas City sits in the transition zone, where nothing is completely at home, and turf-type tall fescue is the closest fit going: the deepest roots of the cool-season grasses, the most heat and shade tolerance, and a tolerance for soil pH anywhere from 4.7 to 8.5. It still loses plants every summer.
There are two ways to get new seed into a lawn. Broadcast seeding after aeration is the standard method, and it is the right one for a lawn that has thinned out but still has grass across it, because the surface has just been opened and the plugs crumble back over the seed, which is the soil contact it needs. The holes themselves are not where the seed is meant to end up; seed at the bottom of one is deeper than it should be.
Ground that is actually bare wants a slit seeder or a verticutter, which cuts furrows and drops seed into them, and that costs more than broadcasting. Johnson County Extension says core aeration alone gives a less uniform stand and lengthens the time bare areas take to fill in. Which one your lawn needs depends on how much grass is left in it, and I will tell you which when I look at it.
The seeding window
University of Missouri puts the seeding window for cool-season grass at August 25 to October 10, and says lawns seeded within a week of Labor Day are more likely to fill in completely by winter.
- Aug 25 to Oct 10The MU window for cool-season seed in Missouri.
- Early to mid SeptemberThe Johnson County Extension ideal: soil still warm, nights cooling, rain more likely. Seed goes by soil temperature, and the soil is still warm then.
- Out to about October 15Johnson County Extension says conditions are often still right that late, with good results. Seed that goes down later has fewer growing weeks before winter.
- Spring, if fall gets away from youCold soil slows germination, summer annual weeds come up alongside it, and the only preventer that can go down with new seed is mesotrione, at its lowest rate. The MU line on spring seeding is that April is already too late.
How a seeding visit goes
- Aeration first, in more than one directionOpen holes everywhere the seed is about to land.
- The rate gets split and crossedHalf the seed one way, half across it. Even coverage beats a heavy single pass, and heavy is its own problem: K-State warns that heavy seeding can lead to overcrowding, poor rooting and disease problems.
- Bare ground gets the other machineIf the yard is more dirt than grass, broadcasting into cores is the wrong tool and I will quote the slit seeding instead.
- Then your watering decides itFor about two weeks the lawn needs the opposite of what an established lawn needs. That part matters more than anything I did with a machine.
Watering new seed
Light and often, so the surface never dries out. Johnson County Extension wants the upper surface of the soil damp at all times.
- Short waterings, one to four times a day, wetting only the top half inch. MU puts it at an eighth to a quarter inch a day.
- Not one long soak. A deep soak runs off clay and the surface still dries by afternoon, and a dry surface kills a germinating seed.
- Once the seedlings are up and rooted, move back toward less often and deeper. Daily watering is wrong for every lawn except a new one.
- First mow when the new grass reaches about three inches, on a dry day and with a sharp blade.
The spring product that stops your fall seed
A crabgrass preventer works by killing seedlings as they emerge. It cannot tell fescue seed from crabgrass seed. The K-State residual figures are the part people miss: prodiamine at a full rate gives over six months of control, dithiopyr three to four months. A full-rate April application can still be working when September seed goes down, and then nothing comes up and nobody can say why.
So the spring decision and the fall decision are one decision. If you know you want to seed in September, the spring pre-emergent has to be chosen and rated with that in mind, or left off the areas being seeded. If a full rate already went down this year, tell me what it was and roughly when, and I will read the reseeding interval off the label before you buy seed you are going to waste.
One product family can go down at seeding time. Siduron used to be the answer and is not manufactured any more. Mesotrione is what is left, at the lowest label rate, and K-State notes establishment is still slightly reduced. Going the other direction, the Purdue table says a prodiamine application waits 60 days after seeding or until after the second mowing, whichever comes later.
Questions I get
How fast will I see grass?
Seven to fourteen days in September soil, and as little as four to seven in a warm week with rain. It looks like nothing happened for the first week. Thin seedlings do not cover ground for a month after that.
Can you seed without aerating?
I can, and it is usually a waste of your money. Seed lying on top of thatch feeds birds. Soil contact is the entire reason aeration and seeding go together.
Would twice the seed give me twice the grass?
No. Thickening a thin lawn takes three to four pounds per thousand square feet. Bare ground takes six to eight. Past that the seedlings crowd each other and you are paying to make the stand weaker.
Does a lawn need seed every year?
Not usually. The MU guidance for a maintained lawn is overseeding along with aeration every three to five years. A lawn that thins out every August, or one that took a bad summer, is a different conversation.
Seed goes in behind the aerator
Broadcast seeding is quoted with aeration because it depends on it.
Get a quote for seeding
Tell me the address and whether the lawn is thin or actually bare. Those are two different jobs at two different prices, and I will say which one I think it needs.