When to Overseed a Lawn

Overseeding is most effective when your lawn is growing most actively. Deciding when to overseed your lawn depends on whether your existing grass is a warm or cool-season type.

Experts recommend overseeding most lawns in the late summer or early fall, at least six weeks before the first frost. The rules change for when to overseed a lawn in southern areas where grass grows more actively in the spring. 

In this article, we’ll cover:

• Overseeding Cool-Season Grasses
• Overseeding Warm-Season Grasses
• Overseeding transition Zone Grasses
• How Frequently Should You Apply Grass Seed?
• FAQs about Overseeding

When to Overseed Cool-Season Grasses

Popular in the northern states, cool-season grasses grow most actively in spring and fall. These grasses should be overseeded in late summer or early fall. This way the seeds will have time to germinate before your lawn comes out of dormancy in the spring. Most weeds have stopped growing by fall, so your new grass seed will have less competition. 

Ideal conditions for growing cool-season grasses are when the soil is between 50 and 65 degrees. You can use a soil thermometer to check this out. 

There are many varieties of cool-season grasses, but the most common ones include:

• Perennial ryegrass
• Kentucky bluegrass
• Tall fescue
• Fine fescue
• Chewing fescue

Another thing to consider when overseeding is when you expect the first frost. It’s important to overseed at least 45 days before the ground freezes so the new seeds have time to take root. Any closer to the first frost than that, and the grass seeds may die.

Overseeding Warm-Season Grasses

Warm-season grasses are most active in late spring and early summer and best for lawns in the southern United States. It’s best to overseed with warm-season grass seeds in the late spring or early summer when soil temperatures are between 70 and 90 degrees. These types of grasses prefer prolonged temperatures around 75 degrees and lie dormant during winter.  

The most popular kinds of warm-season grasses are drought-tolerant. They include:

• Centipedegrass
• St. Augustinegrass
• Bermudagrass
• Zoysiagrass
• Bahiagrass
• Buffalograss

You may want to overseed your warm-season grass with a cool-season variety such as ryegrass. This will help your lawn stay green longer into the winter season. If this is your goal, you need to overseed in the fall, ideally when the soil temperature is between 50 and 65 degrees.

Ryegrass Options

Annual ryegrass will provide winter color in the far South, while perennial ryegrass is better suited to lawns in the middle of the country. Perennial varieties will lie dormant through the summer and return next fall. The extreme temperatures in the South are not hospitable to perennial ryegrass, so you’ll want to overseed with annual ryegrass each autumn.

Overseeding Transition Zone Grasses

You’ll want to consider blending grass types in states near the Mason-Dixon line. Summers tend to be too warm for cool-season grasses, but winters are too cold for warm ones. 

Home supply stores typically sell grass seed mixes, especially for the transition zone. You’ll find overseeding with this mixture is a great way to keep your lawn green and healthy year-round.

Transition zone grasses should be overseeded in the first few weeks of spring when the existing lawn first turns green.You want to overseed when your lawn is at its most active, but you also want to be sure you have enough time to complete the process.

How Frequently Should You Apply Grass Seed?

Most lawns will require overseeding every couple of years, but you may want to make it an annual chore if your lawn suffers from: 

• Heavy traffic
• Insect damage
• Disease 
• Drought conditions

You’ll find valuable information on the seed packaging specific to each type of grass. The labels will indicate how much seed to apply per square foot, as well as other tips for attaining a healthy lawn.

FAQs About When to Overseed a Lawn 

1. How much grass seed should I use when overseeding? 

Apply 6 to 8 pounds of seed per 1,000 square feet on bare soil. Using too little will leave bare spots and patches. Too much seed will force the grass to compete for water, light, and other nutrients. Read the directions on the seed package. 

2. Should I mow the lawn before overseeding?

Yes. Before overseeding, cut your grass shorter than usual and bag the clippings. It’s important to loosen the top layer of solid and remove any dead grass or thatch so the grass seed can easily take root and germinate.

3. Should I use a weed treatment while overseeding?

This is a big no-no. Pre-emergents herbicides work by preventing germinating seeds from establishing roots. These products don’t know the difference between weed seeds and grass seeds. You also want to hold off on post-emergent weed treatments since they can kill young grass seed.

4. How long after overseeding will I see grass start to grow?

It takes two to three weeks for germination to begin. With proper watering, you should see the grass sprout within four weeks. It will take about eight weeks to see a fully established lawn.

5. How soon and how often should I water the lawn after overseeding?

Water the overseeded area lightly right away, for about half an hour, to force the seed into the soil. A light spray is best so as not to wash away the grass seed. You’ll want to water two or three times a day for the first week, and then once a day for the next three weeks.

Overseeding is easy enough to do as a DIY project. But you might not want to spend your time checking soil temperatures, dethatching, and aerating. We can help you find a lawn care professional near you who will overseed your lawn and help it grow.

Main Photo Credit: Pxhere