Overseeding Cool-Season Grass

Overseeding your grass is the process of adding grass seed to the soil without having to till or tear up your yard. We break down the six steps to overseeding cool-season grass.

Overseeding improves the appearance and thickness of your lawn, and it helps crowd out weeds. It keeps the grass young and thriving. Finally, it fills in those bare spots left from any lawn damage during the summer months.

This task is an easy do-it-yourself project. By following the steps in this article, you will create a beautiful lawn.

Six Steps to Overseeding Cool-Season Grass

Soil Test
Aeration
Overseeding
Fertilization
Watering
First Mow

Soil Test

It is essential to perform a soil test on your lawn to make sure you add the appropriate amount of macronutrients for the best stand of grass. Macronutrients are nitrogen (N), phosphorus (P), and potassium (K).

A soil test determines which nutrients your soil is lacking. By knowing which macronutrients are missing or low, you can add those back into the soil with fertilizer.

Gather Soil Samples

With a shovel and a bucket, scoop small samples (about a handful) of soil from different areas of your yard. Place the soil in the bucket. The soil needs to be dry, not muddy.
With your hand, mix the soil and remove any grass clumps and rocks.
Place the dirt in a zip-top bag.
Take it to your local Agriculture Extension office.
The Agriculture Extension office will get your results to you within a few weeks.

To see a sample soil test submission sheet, check out this link.

Soil Test Results

Your soil test results include a summary with the recommended fertilizer numbers (#-#-#). When you get your soil test results back, go to your local co-op or garden center and pick a bag with similar numbers or closely matching numbers. Check to make sure it is enough fertilizer to cover the square footage of your yard.

Aeration

Aerating your yard does what it says. It improves the airflow in your soil. Over time, the earth can become compacted, which reduces the ability for fertilizer and water to reach the roots of the grass.

You don’t need to buy any fancy, expensive equipment or spiked shoes you see online to aerate your yard. Aerators are available for rent for half a day or a full day. A local equipment rental business likely carries them.

Before aerating, gather all the necessary supplies to complete the overseeding process:

Fertilizer
Grass Seed
Spreader
Sprinkle

How to Aerate

To aerate, walk behind the aerator following the pattern illustrated here.

Follow the purple arrows for the first pass around the perimeter of your lawn. On the second pass, follow the purple arrows, but the path should be to the inside of the previous one. The blue arrows indicate the third path, and the red arrows the last course.

Be sure to watch for tree roots, water meter covers, and irrigation heads/valve boxes. The aerator can damage these.

The aerator pulls plugs of dirt out of the soil. Leave the plugs in your yard. Over time, the plugs will break up.

Overseeding

Overseeding is the act of spreading seed over existing grass to thicken the stand.

Helpful Tip:

We recommend purchasing seed from one of the national suppliers. If you buy the seed and spreader from the same company, the company makes it very convenient with explicit instructions on the back of the bag.

Types of Spreaders

For homeowners, there are three types of spreaders.

Handheld rotary spreader
Drop spreader
Broadcast spreader

The handheld rotary spreader holds a small amount of seed and broadcasts the seed over a small area. This type of spreader requires many refills to cover a space. We don’t recommend them for an overseeding project.

A drop spreader is a walk-behind spreader. As you walk, the spreader drops the seed or fertilizer directly to the ground. This type works best on small yards.

The broadcast spreader is ideal for medium to large yards. This walk-behind spreader throws seed out from the base. It casts the seed or fertilizer over a larger area covering more square footage than the other spreaders.

How to Spread Grass Seed

Pour the grass seed in the spreader, set the spreader dial (since you are covering the same area twice, you will set the dial to half of what the instructions recommend), and start walking.

When spreading grass seed, make sure you get ample coverage of your lawn. Follow the same pattern as the aeration one above, with one exception. You only make one pass around the perimeter of the yard, not two. This pattern provides the best coverage and assures that seed is spread to all areas of the yard.

Once you have covered the entire area, save the remaining grass seed. If you see that you missed a few spots after the grass sprouts, use the rest of the seed to cover those areas. Do not save the seed for next year. It can rot and mold.

Applying Fertilizer

Check the back of the fertilizer bag for the setting of your spreader. Pour the fertilizer into the spreader. You walk in the same pattern you did when spreading the grass seed, ensuring complete coverage. If any fertilizer is remaining, pour it back into the bag and close tightly for future use.

Watering

For successful fall overseeding, watering is a MUST. Watering in the morning is optimal. A basic rotating sprinkler does the job perfectly.

Make sure the sprinkler can water all of the overseeded areas. You may have to move the sprinkler to reach all of the lawn. The grass should be watered thoroughly but not to the point of creating runoff water.

We recommend checking the water every 15 minutes until you get a gauge of how long it takes to saturate the lawn. It depends on the type of soil you have as to how long it takes for water to penetrate deeply.

Cutting New Grass

When you cut the grass for the first time after overseeding, your mower must have sharp blades. New grass doesn’t have a strong root system yet. If you mow with a dull blade, you are likely to pull the grass seedlings out of the soil. The grass should also be dry for the initial mow.

Mow Height

For tall fescue, the best mowing height is 2-3″. For fine fescue, it is 1.5 to 2.3″. Only remove 1/3 of the grass blade. For example, if the grass blade is 3″ tall, remove 1″. Scalping (cutting too short) the grass will cause the grass to weaken and increase the prevalence of weeds. If your grass gets too tall between mowings, lower the height gradually over several mowings.

Mowing Tip

Do not mow in the same direction for each mowing. Alternating directions keeps the soil from becoming compacted and helps the fescue to grow upright.

For a video tutorial on how to aerate and your yard, check out our Youtube video.

If you have any comments or questions about overseeding cool-season grass, let us know below.