If your lawn’s looking a little thin, overseeding can restore it to a thick, healthy condition in just one season. In a southern climate, it can extend your lawn’s growing season. It’s a fairly easy job, but to get good results, you’ll need to choose the right grass seed, determine the best time of year for your climate, and prepare your lawn correctly.
Overseeding for Health and Beauty
A lawn can start thinning out for a variety of reasons. Frequent foot traffic is a common one, but heat and drought damage, disease and insect damage, incorrect mowing, lack of nutrients, compacted soil, erosion, too much shade, and the wrong grass type for the climate can also cause a lawn to wear away.
Age is another issue. While grass renews itself and can live for decades, the renewal process slows down as the grass ages, and eventually, blades die off faster than the lawn can replace them.
A thin lawn not only looks bad, but also invites weeds. Overseeding, or applying new seed to an existing lawn, is a fast, easy, and inexpensive way to restore the lawn to full health. Overseeding cool-season grass on a warm-season lawn also gives the lawn color over the winter after the warm-season grass has gone dormant.
When to Overseed
How often to overseed depends partly on your grass type. Sod-forming grasses, such as bermudagrass (Cynodon dactylon), zoysiagrass (Zoysia sp.), Kentucky bluegrass (Poa pratensis ), bentgrasses (Agrostis spp.), and Chewing’s red fescue (Festuca rubra ssp. commutata) use rhizomes, stolons, or tillers to spread laterally, so they can fill in thin spots fairly easily. These only need overseeding when noticeably thin spots appear, which might be every three or four years or even less often.
Bunch-type grasses, such as most types of tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne), don’t spread well, so thin areas can quickly turn into bare spots that won’t clear up on their own. These grasses benefit from annual overseeding to prevent thin spots from developing.
The best time to overseed cool-season grasses in the north is late summer or early fall when daytime air temperatures have cooled off for the year, but will stay above 55 degrees for the next several months. This time of year means less threat from weeds. Spring is the next best time.
In the south, overseed in mid-spring or early summer when the soil temperatures are at least 65 degrees consistently. In any climate, avoid overseeding during the middle of summer when the risk of heat stress, drought, and disease is highest.
Finding the Right Seed
A variety of grass types can be used for overseeding, depending on the grass you already have and your lawn’s needs. Nurseries often sell blends of grass seed chosen to thrive in the local region. They can also update you on new cultivars that offer benefits your existing grass doesn’t. Mixing your own seed blend is also an option.
A blend of fine-blade Kentucky bluegrass and turf-type tall fescue is common for thickening cool-season lawns. Pay close attention to the cultivar and avoid overseeding fine-blade grass with a coarser cultivar that will stick out. To restore the lawn in shady areas where most grass grows poorly, consider overseeding with red fescue.
If your goal is to bring winter color to your bermudagrass or other warm-season grass, choose a species that will grow through winter, but go dormant or die before summer. This way the overseeded grass won’t compete with your existing grass.
Annual ryegrass (Lolium multiflorum) is a popular choice. Creeping bentgrass (Agrostis stolonifera), although more expensive, also works well. Perennial ryegrass can be used in the warmest southern climates, but it stays active too long in spring to be used in areas cool enough for fescue to grow well.
Preparing Your Lawn
Preparation is critical to the success of your overseeding. For anything beyond preventing or correcting normal thinning, test the soil, and add soil amendments as needed. For soil compaction and excess thinning from foot traffic, consider installing stepping stones.
If you’re overseeding to thicken the lawn, start by cutting the grass down to two inches or less. If you want to add winter color to a dormant southern lawn, cut as low as you can. Bag the clippings. Rake the soil with a metal thatch rake to remove thatch and debris, and to loosen the soil so seeds can root more easily. If the soil is compacted, core aerate to let more air and water reach the soil.
Once the lawn is dethatched and aerated, rake in a thin layer of enriched soil to help the seeds get started. Around 1/4 inch or less is enough to give the seeds extra nutrients, but any more can smother your existing grass.
Adding the Seed
To thicken a generally thin lawn or prevent thinning, you’ll need between 1 to 4 pounds of seed per 1000 sq. ft. To repair extremely thin or completely bare spots, you’ll need up to 5 pounds per 1000 sq. ft. Different grass types have different coverage rates for overseeding, ranging from 1/3 pound to 5 pounds, so check the recommended overseeding rate for your seed before you start.
If you reseed every year, you’ll need less seed in the following years. Apply your seed with a seed spreader then immediately water it in with an inch of water.
After overseeding, keep the soil consistently moist. Start with frequent, light waterings twice a day for the first four days, then water daily. Once the grass has germinated, which can take up to two weeks, water deeply every few days. When the seedlings have reached the height of the rest of the grass, continue watering deeply every few days for a week, then water as recommended for the type of grass. Starter fertilizer can help, but avoid any product containing herbicide, which can prevent seeds from germinating.
Overseeding is a simple, affordable way to keep your lawn looking lush, but it does take some prep work. If your lawn has problems beyond normal thinning, take steps to improve the soil and prevent future excess damage before you overseed. Preparation combined with the right seed at the right time should get your lawn back into shape within weeks.