How to Plant Grass Seed on Existing Lawn | 4 Steps

When your lawn is patchy or dying, you don’t have to tear it up and start over. In most cases, you can spread fresh seeds right over the top, and restore your lawn to its former glory. So, how do you plant grass seed on an existing lawn?

To plant grass seed on an existing lawn, you first need to prepare the lawn by mowing, raking, and aerating. Next, you need to spread the seed according to the instructions on the package. Finally, you should spread a high-phosphorous fertilizer, and water the area twice a day for at least two weeks.

The process of spreading fresh seed over old grass is called overseeding, and it’s a normal part of healthy lawn maintenance. Here, we’ll talk about the basics of overseeding, as well as some of the nitty-gritty details. By the time we’re done, you’ll know what seeds to plant, when to plant them, and how to follow up.

What is Overseeding and Why is It Important?

Overseeding means spreading new grass seed over an existing lawn. This can be done as a spot treatment, to fill in heavily-worn patches, or over the entire lawn if the grass is starting to thin out. Regardless, the goal is the same: filling in the lawn so it’s thick, full, and healthy.

Overseeding isn’t just for “sick” or “damaged” lawns. In many parts of the country, grass will die off throughout the summer, and the lawn will thin out. In these areas, overseeding is an annual routine.

How to Add Grass Seed to Your Existing Lawn in 4 Steps

1. Prepare Your Existing Lawn

Before you start overseeding, you first need to prepare the area. Start with a good watering the day before, so any living grass will be nice and perky. Mow your lawn on a lower setting and use the bagger instead of the mulch option to keep the clippings from getting spread around.

garden rake and aerate tool for prep work

Next, rake your lawn to remove any debris like dead grass and leaves. Remember, your seeds will only grow if they’re actually in contact with the ground. This kind of debris can keep them from taking root.

As a final step before you spread your seed, aerate the lawn. Use a gas machine or manual aerator that removes plugs between 0.5 and 0.75 inches in diameter, and 2 to 3 inches deep. This will loosen up the soil and make it easier for the young grass to grow.

2. Spread Your Grass Seed

spread grass seed

Spread your grass seed at the rate recommended on the label. This will be different depending on the seed type, and whether it’s a single species or a mix. A broadcast spreader is best for covering your whole lawn since you can get the job done quickly. Hand spreading is fine for smaller patches.

3. Fertilize

Fresh grass requires good fertilizer to grow, particularly fertilizer that is rich in phosphorus. Keep in mind that some locations restrict the use of phosphorus in lawn fertilizers, so you may only be able to use a nitrogen-based fertilizer instead.

fertilize lawn after overseeding

Keep in mind that some grass seed mixes come with fertilizer already blended in. In that case, check the manufacturer’s instructions regarding any additional fertilization.

4. Water Your Seeds

water lawn after overseeding and fertilizer

When you’re done planting, the final step is to water your freshly-planted seeds. For the first two weeks or so, you’ll want to water lightly two to three times per day. This shallow watering will keep the seeds wet and encourage them to sprout. Afterward, you can scale back to watering a few times a week, but for longer periods. This will soak deeper into the soil, encouraging healthy root growth.

Things to Consider When Planting Grass Seed Over Your Existing lawn

Seed Your Lawn During the Best Possible Time of Year

The best time to seed your lawn depends on your local climate. The goal is to allow the grass to grow strong roots before weather becomes unfavorable. In colder climates, this means the grass needs to establish before winter sets in. In hot climates, it means planting before the weather gets too hot.

In the northern states, this means overseeding about six weeks before the first hard frost. This might be anywhere from early August to late September, depending on where you live.

In the south, it depends whether you’re in the east or in the west. From central Texas through California, early spring is the best time of year. From the Texas gulf coast through to Florida, anywhere from mid-April to early June is a good time for overseeding.

Choosing the Best Possible Grass Seed (Location Matters!)

The best type of grass is going to depend on a handful of factors. These include your local climate, soil conditions, and whether you’re planting in the sun or in the shade.

In southern climates, Bermuda grass is a popular choice for its durability. Zoysia grass and centipede grass grow well in the dryer conditions of the southwest, while Bahia grass is better for the humid southeastern US.

Annual ryegrass is a bit of an oddball. It’s traditionally used as a hardy, cold-weather grass where conditions are too harsh for perennial ryegrass. That said, it’s hardy enough to survive warmer conditions as well. As a result, it’s a popular choice in warmer climates, since it will thrive in the winter.

Kentucky bluegrass is one of the most popular choices in northern climates. It has a rich green hue, and it grows thick and strong. However, it requires plenty of sun, and thins out easily in the shade. In shadier areas, it’s better to use a mix of Kentucky bluegrass and perennial ryegrass.

Tall fescue is the lowest-maintenance option, but it’s only suitable for cool, dry climates. In humid climates, it’s vulnerable to fungal infection. Red fescue, on the other hand, thrives in cool, humate regions. Not only that, but it grows very densely, which helps cut down on weeds. On the downside, red fescue only grows well in the shade, and scorches easily in the sun.

Cover With Organic Matter

When you spread seeds on the ground, you’re basically spreading bird feed. And while that sounds like a nice thing to do, the last thing you want is for a bunch of birds to come by and eat up all your seeds. To avoid this, you want to cover your freshly-spread grass seed with a safe, organic material.

Compost is ideal for this purpose. You can use fresh compost from a compost heap, or buy some from a garden center. The key is to spread only a thin layer, about ¼ inch. Much more than that, and you can smother the seeds, preventing them from germinating. Ideally, you’ll want to see around 10 percent of your seeds peeking through the compost.

For small areas, you can simply spread your compost by hand. For larger areas, you can use a shovel, pitchfork, or even the spreader you used for your seeds.

Compost has a couple of benefits, in addition to covering your seeds. First, it provides valuable nutrients to your fresh grass. Secondly, it breaks down naturally into the soil. By the time the grass has grown in, the compost will basically be gone.

That said, compost can also be smelly, particularly when spread over a large area. If that’s a concern, you can use hay or straw instead. Straw is better since hay is full of seeds, which can sprout alongside the grass and mar your lawn.

Keep in mind that a lot of hay and straw is treated with pesticides, which can linger for years and damage nearby plants. When at all possible, buy hay that’s certified organic, or from a local farm where you can verify that it’s pesticide-free.

Properly Water Your Overseeded Lawn

Proper watering techniques for your grass will depend on where it is in the growing cycle. Prior to germination, you only want to wet the top inch or so of soil. This takes only about 15 to 20 minutes of watering, but it needs to be done two to three times per day.

Once new grass blades are starting to grow, you no longer need to encourage germination. Instead, you want to promote deep, healthy roots. To achieve this, you need to wet the soil all the way down to around three inches below the surface. This takes anywhere from 45 minutes to an hour, but you only need to do it three times a week.

After the grass has been growing for six weeks, it should be thoroughly established. At this point, you can scale back to ordinary “maintenance” watering about once a week. In dryer parts of the country, you might need to water twice a week, if water restrictions allow for it.

Related Questions

What Do You Put Down First – Grass Seed or Fertilizer?

It depends on the grass. Cool-season grasses benefit the most from fertilizing after planting. Examples of cool-season grasses include ryegrass, fescues, and Kentucky Bluegrass. Since these are the most commonly used grasses in the US, we wrote our guide with that in mind. That said, warm-season grasses like zoysia and Bermuda grass thrive when they’re fertilized before overseeding.

Another option is to mix the seed and fertilizer together in the same spreader and apply them simultaneously. In theory, this saves work, but you need to be careful to thoroughly mix both materials. Otherwise, you can end up with too much seed in some areas, and too much fertilizer in others.

Can You Plant Grass Seed Over Dead Grass?

Dead grass, or any other debris, will keep grass seeds from making contact with the soil, and they won’t be able to grow. As a result, you should rake prior to overseeding to remove small amounts of dead grass.

If you’ve got a lot of matted dead grass – called thatch – you’ll need to rent a dethatching machine to break it up. You could also buy a manual scarifier, which is cheaper, but very labor-intensive. Either way, it helps if you mow first, since mowing will reduce the amount of grass cover and clear any non-matted debris.

Do You Need to Aerate Existing Lawn Before Seeding It?

Not necessarily. The purpose of aeration is to loosen up the soil, which improves oxygen flow and allows water and nutrients to penetrate. This doesn’t just speed up germination; it also helps the freshly-germinated seeds to grow deep, healthy roots.

If your soil is already loose or spongy, you can often get away without aerating. That said, if your soil is dense or rich in clay, you definitely need to aerate.

Finally, when in doubt, just aerate. Otherwise, you might go through a lot of other trouble only to get poor results.

Final Thoughts

As you can see, overseeding your lawn is a simple, four-step process. You prepare the area, you spread the seed, you fertilize, and you water. But the devil is in the details. You need to prepare thoroughly, select the right seed and fertilizer, and provide the right amount of water. If you can do all those things, you’ll have a lush, beautiful lawn in the springtime.

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