If you’re aiming for a lush, green lawn that your neighbors envy, overseeding can help. By spreading grass seed over existing lawns, this practice fills in any gaps, prevents thinning, and contributes to a healthy lawn.

To get the full benefit from overseeding, you’ll need to do it the correct way. The best practices depend on the grass type you select, so there isn’t one set of directions that apply to every lawn. However, fescue is an appropriate grass choice for much of the US, so we’re going to focus on the best practices for overseeding lawns with fescue.

How to choose grass seed

Depending on where you live, you’ll want to select either a cool-season grass or a warm-season grass. Fescues are cool-season grasses well-suited for most of the US, with the exception of the deep South and parts of the Southwest. If you live in the blue shaded area of the map below, fescue will work for overseeding your lawn.

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Once you decide on fescue, you’ll need to choose exactly which type you wish to use. Fescues are separated into two main types: tall fescue and fine fescue, which includes chewings fescue, red fescue, and hard fescue.

Tall fescue can tolerate high temperatures better than fine fescue, but it isn’t as shade tolerant. To choose the best fescue type for your lawn, consider your climate and environmental conditions.

When you’re selecting a specific product, look for a grass seed that is free of weed seeds, has a high germination rate, and was packed within the past year.

When is the best time to overseed

The best time to overseed depends on the type of grass seed you’re using.

For cool-season grasses like fescue, the best time to overseed is in the early fall just as the weather is getting cooler. The soil is still warm enough to allow for adequate germination, and the cool air encourages vigorous plant growth.

Preparing your lawn for overseeding

In order for new seed to establish itself, you need to provide a quality environment for germination and growth. Before you broadcast any seed, complete the following steps.

Conduct a soil test.

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To check the pH and nutrient levels of your soil, collect a soil sample, and send it to a local soil lab. Most land grant universities have labs that can test your sample and provide you with both results and recommendations.

Amend your soil.

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Photo credit: Cade Martin, Dawn Arlotta, USCDCP

Utilize your test results to add fertilizer and/or lime to your soil. Not only will this provide your new grass with the nutrients it needs to establish, but it will also supply a boost to your existing lawn.

If you didn’t conduct a soil test, you should still apply a starter fertilizer before overseeding. Look for a product with an NPK ratio of 10-10-10, 18-24-12, or 5-10-5. Apply the product at a rate of 0.5 lb nitrogen per 1,000 square feet.

Mow and rake your lawn.

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Photo credit: Andres Siimon

In order for the seed to germinate and form strong roots, it needs to make contact with the ground! The first step in making sure this is possible is mowing your existing grass close to the soil surface. After you do so, rake your entire lawn to remove any dead grass and debris that could impede the seed’s contact with the soil.

Dethatch and aerate

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Photo credit: Gord Webster

Another factor that can inhibit seed contact with soil is thatch. Thatch refers to a buildup of both living and dead matter including rhizomes, grass trimmings, and stems. To see if you’ll need to dethatch your lawn before overseeding, try to access the soil with your fingers. If the thatch inhibits this, it’s time to get to work removing it.

To remove thatch, you can use a dethatching machine that’s meant for the job. Or, if you’re up for a challenge and have a small lawn, you can aggressively rake until you loosen the thatch. No matter what method you use, make sure to remove the loosened and exposed thatch from your lawn.

Unless your soil is already loose and well-aerated, it will pay off to aerate your lawn before overseeding. To do this, rent or buy a core aerating machine. These remove small plugs of soil, allowing for increased percolation and aeration, which helps build a strong root system.

It’s best to aerate when the ground in moderately moist, as dry conditions can cause unnecessary wear on both the machine and the operator.

Boost your lawn by overseeding

Once you’ve completed the preparation steps listed above, it’s time to start spreading your selected seed. Depending on the size of your lawn, you can use a hand-held seeder or a push seeder. No matter what type of seeder you use, make sure to calibrate it so it evenly dispenses the correct amount of seed.

The overseeding rate is half of the rate used to establish new lawns. For tall fescue, this ends up being 3-4 pounds per 1,000 square feet.

After you apply the seed, spread a thin layer of compost to increase germination, and provide a dose of organic matter. Next, water in your new seed.

Provide the proper maintainance

After you’ve seeding your grass, you still need to take some steps to encourage growth. Continue watering twice a day until your grass seed germinates. Tall fescue generally takes between one and two weeks to germinate.

One key tip is to avoid mowing soon after overseeding! If you mow the new grass before it has a chance to establish strong roots, you can rip the young blades out of the ground. To be safe, wait three to four weeks after overseeding, and mow higher than you normally would.

While it may seem obvious, you’ll also want to delay applying any herbicides. When the overseeded grass is young, it is more susceptible to damage. So, wait until your entire lawn is established before applying herbicides.

Green up your lawn by overseeding

While you may not think of adding grass seed to an already established lawn, overseeding will keep your green spaces healthy for years to come. By following the best practices we’ve outlined above, your lawn will be in prime shape when spring rolls around next year.