How to Overseed a Lawn
Many homeowners dream of having a lush lawn all summer long! The best way to achieve that: overseeding. As time passes, lawns can grow thin and unhealthy, and weeds will begin to take over. Overseeding will help fill in bare spots, establish improved grass varieties, enhance the color of the lawn, and leave little room for weeds to grow.
Time of Year
The best time of year to overseed a lawn is in the fall when you use cool season grass like Kentucky bluegrass, fescue, and perennial ryegrass. In autumn, the soil is still warm enough that the seeds can germinate, and the cool air helps grow a strong root system. For many parts of North America, this means that September is the best time to overseed. Grass seed grows best when temperatures are about 50°F, and it's not yet freezing temperatures at night. If you can't do it in the fall, spring is the next best time.
It's easiest if you get rid of as many weeds as possible before you start the process of overseeding. This opens up more spots for grass to grow and you won't have to worry about weeds later. You can get get rid of weeds using a weed killer, or if you're against using pesticides, you can pull them out individually either using your hands or with a weed puller.
Cut the Grass
The next step in preparation to overseeding your lawn is to cut the existing grass so it's just above the soil line—likely an inch to an inch and a half. You want it short enough that the sun can reach the soil. If your lawn mower doesn't collect the grass clippings, take the time to rake them along with the thatch. Thatch is a layer of dead organic matter that gathers on top of the soil. Thatch and grass clippings will make it harder for the seeds to germinate after you spread them, so remove them as much as possible.
An aerator is another great way to remove thatch. As well as collecting thatch and grass clippings, it also helps to loosen the soil, which makes new grass grow faster. A lot of lawns experience heavy foot traffic, which really packs it down.
Now that your lawn is prepped, it's time to spread out the seeds. A lot of people choose to use a seed spreader, which can help spread the grass seeds evenly over the lawn. Other people choose to just sprinkle it around using their hands. Either way, make sure to follow the instructions on the back of your seed packaging. It will let you know how much seed to sprinkle.
Apply Slow-Release Fertilizer
A slow-release fertilizer will provide nutrients to help your grass grow. Make sure you find a fertilizer that works for your specific lawn conditions, which you can find out from using a soil test to determine the pH of your soil. These tests come in kits and are available to purchase either online or at most hardware and gardening stores.
You should water your lawn immediately after laying down seed and fertilizer. You will then want to water it frequently, several times a day over the next few weeks, to make sure your seeds germinate properly. In the beginning of the process, the seeds must stay moist at all times to work. Once the grass begins to grow, you can water it less.
Now that the hard work is done, you have to do a bit of maintenance to ensure your overseeding works. You should fertilize the lawn again six weeks after applying the seeds. Too much quick-release fertilizer can burn the new germination and seedlings, so don't go overboard; follow the instructions on the package. Once the grass reaches about two or three inches, make sure to mow it. Then, for the rest of the season make sure to mow the lawn to a height of two inches—but only when the grass is dry.