Aeration and Overseeding Guide for Lawns

One of the biggest misconceptions of lawn management among homeowners is that left on its own, grass will grow and produce a full rich lawn naturally. Unfortunately, that is not the case. If you do want that uniform full look, you will need to take some steps to achieve it. Both overseeding and aeration can help get the desired results. Together these techniques help to create a beautiful thick, green, and lush lawn, and in today’s aeration and overseeding guide, I’ll explain why these two projects are a match made in heaven.

Whether you want to create a new lawn or revitalize grass following a harsh summer or winter, spending a weekend on aeration and overseeding your lawn can bring your turf back to life.

In today’s guide you can read about these techniques and learn how to prepare for and execute this weekend project. This lawn renovation can quickly transform your yard into the best on the block.

If you’ve never tackled a lawn renovation project before, aeration and overseeding can present some major challenges if handled the wrong way. So I’ll also discuss some common mistakes people make (and how you can avoid them).

Let’s get into it!

A good place to start is by explaining what aeration and overseeding are and why these lawn projects work so well together.

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About Aeration and Overseeding

• Aeration is the process of de-compacting the soil in your yard by cutting small holes into it. These holes allow oxygen, water, and fertilizer to reach your grass’s roots, which strengthens your grass.
• Overseeding is a process for improving your yard by adding fresh grass seed to your existing lawn to thicken and revitalize your turfgrass.

While these are two separate techniques for improving your yard and lawn, when combined into a single weekend project, these two tasks work in harmony and can help improve the health of your grass for the next several years.

The holes created by aeration allow grass seed and starter fertilizer to achieve better soil contact, which improves results.

More About Overseeding

Overseeding is the act of adding new grass seed into an existing patch of soil without turning it over and starting anew.

In other words, you won’t need to kill your existing lawn. You’re just adding new grass seed to revitalize an existing lawn, thicken it, and fill in thin or bare patches in your grass.

It is a relatively easy method for filling in open spots in your lawn and achieving a fuller look. Personally, I overseed my lawn once every 1-2 years.

More About Core Aeration

While there are several reasons you may aerate a lawn, typically this project is to loosen soil and eliminate compaction.

Aeration breaks up layers of soil by cutting holes into your existing turf. This allows oxygen and water to flow into the soil and stimulates your grass to grow larger, more healthy root systems.

Roots grow deeper in loose soil. This, in turn, makes the grass plant stronger and your lawn will be thicker and healthier as a result.

Core aeration is an ideal way to support your existing grass and build a lawn that boasts resilient grass. A healthy lawn will crowd out weeds naturally without reliance on harmful herbicides.

What the Experts Recommend

Tom Kaib, an Extension Horticulturist at North Dakota State University, says that “Hollow tine or cone aerators are [the] best” types of aeration equipment. He recommends staying away from spiking and solid-tine devices, as they can lead to more compaction in your soil. 

When you do core aeration, Tom recommends removing the “cores as deeply as possible.” It’s best to aerate moist (rather than wet) soil.

He offers spring and early fall as the best times to aerate your turf.

How (and why) to Use Aeration and Overseeding Together

While both aeration and overseeding are separate techniques to improve your lawn, they can (and should) be used together to create a rich, vibrant lawn.

Overseeding immediately after core aeration allows excellent soil contact for your new grass seed as it falls into the holes you made in your turf.

This improves germination rate, and you simultaneously strengthen existing grass plants while thickening your lawn with healthy new seedlings.

It’s the perfect combination, and these projects can be completed together in a day.

Choosing the Best Time to Aerate and Overseed Your Lawn

In most landscaping and gardening projects, timing is everything. And that’s true for aeration and overseeding.

But there’s not a one-size-fits-all “best” time to aerate and overseed your lawn. Where you live, and the type of grass you have in your yard will dictate when you should tackle these projects.

This is because you want to give the grass time to grow and strengthen before harsher weather conditions arrive, so you want to aerate and overseed your lawn just before your grass has the ideal growing conditions.

Those conditions largely depend on your geographic location and how seasonal changes affect your grass.

That said, here are the best times for aeration and overseeding most lawns:

When to Aerate and Overseed Warm-Season Grasses

If you live in a southern climate, your lawn is probably made up of warm-season grasses. For you, the best time to aerate is during the late spring, and you’ll want to overseed your lawn at the same time.

This is because warm-season grasses thrive and grow best during the heat of summer. By performing these lawn improvement projects in late spring your seedlings will be established just in time for their ideal growing conditions … and they can thrive and develop deep roots throughout the heat of summer.

When to Aerate and Overseed Cool-Season Grasses

If you live in a northern climate with four distinct seasons and snowfall over the winter, your lawn is likely made up of cool season grasses. These grasses thrive in the cooler months of the year (Spring and Fall), and will typically struggle to maintain their green color during the dog days of summer.

For you, early spring (an OK time) or early fall (the ideal time) aeration and overseeding will deliver the best results, with early fall my recommendation.

In spring your window for success is very narrow. Too early and the soil will be too cold for grass to germinate. Too late, and your seedlings won’t have the time they need to develop the root system that will sustain them through the heat and drought of summer, and may struggle to compete with annual weeds.

Fall is best for cool season grasses because annual weeds have faded, soil temperatures are warm from the hot summer months, and the growing conditions are ideal (cool, rainy). By the time winter comes your lawn will be thick and healthy with strong roots, ready to perform well in the spring.

Aerate Your Lawn Before You Overseed

If you are trying to bring your lawn back to life and want a fuller and healthier turf, you probably already know about overseeding.

Still, many people don’t realize that aerating the lawn prior to overseeding is a win-win. I recommend it to nearly every homeowner hoping to improve their yard’s appearance!

Step-by-Step

• Step 1: Provide enough water to the soil as this makes aeration easier. Rain can do the job for you. If not, water the lawn a day before you plan to aerate your yard.
• Step 2: Get to know your aeration machine and its limitations. Some will only cover portions of the lawn so you may need to pass over the same area several times.
• Step 3: Sometimes you will encounter soil plugs as you are passing the aeration machine. While it is easy to ignore these, don’t. Instead, break up these clumps of soil to ensure aeration can be more uniform.

You cannot aerate your lawn properly without machinery, especially an existing large patch of turf. There are three different types of aeration machines available:

• [Good] Spike Aeration: Puts holes in the soils by using a spike. This can work well for lightly compacted lawns, but is not my preferred method.
• [Better] Slicing Aeration: Normally features rotating blades, this type of machine slices through grass, cutting deep into the soil to provide better access to air and water.
• [Best] Core/Plug Aerators: The most common, and the best, this aeration machine is a core/plug aerator. It uses rows of smaller spikes to help remove plugs of soil and bring them to the surface where they can break down naturally in your lawn, leaving behind round holes in your turf.

If you plan to overseed following aeration, I recommend that you mow your lawn pretty short prior to beginning these renovations. This will prevent your existing grass from growing too tall too quickly (and shading out your new seedlings).

Overseed After Aeration

Once aeration is complete on an existing lawn, start overseeding within 48 hours and then water the lawn lightly to ensure good soil contact with your new seed.

During this time window, seed and fertilizer have a better chance of getting deeper into the aeration holes, which is what you want.

Preparation is almost as important as the overseeding itself. Mow your current lawn a little shorter than normal and remove any shavings left behind.

Now it’s time to seed:

Step-by-Step

• Step 1: Check the seed you have chosen to know the recommended rate of overseeding. I like to go a little heavier than the recommended rate so I’m sure to get a nice result. 1.25x the manufacturer’s recommendation seems to be a good number in my experience. Use an online lawn measurement tool to figure out how much seed you’ll need for different sections of your lawn.
• Step 2: Spread the seed around your lawn (either manually or using a lawn spreader). Avoid seeding on a windy day to provide better chance of even distribution.
• Step 3: I like to use a quick-release starter fertilizer that’s high in phosphorous to promote root growth. I usually have this one on hand, so it’s what I use, but Espoma’s organic Bio-Tone product (Amazon link) is really excellent as well. An organic slow-release fertilizers can work OK in the place of a starter fertilizer.
• Step 4: While this is not essential, adding a thin layer of screened compost (around 1/4 of an inch thick) over the lawn can help feed your soil, keep seed moist, and improve your results. It’s a step I recommend, but it is not 100% necessary to get a good result from this project.
• Step 5: Seeds need water, and they need it regularly and at the right time of day. Aim to keep the soil moist with a couple of light waterings per day for a week. I have a guide on this topic here.
• Step 6: The first time you mow your lawn, bag your clippings, then resume normal lawn maintenance after that. Ensure that your newly seeded lawn gets at least 1 inch of water each week. Once your seedlings are established you no longer have to bag your clippings – just mulch them into your lawn.

Common Mistakes (and how to avoid them)

Relative beginners to lawn management may find some challenges when aerating and overseeding their turf. In most instances, problems arise because of some simple mistakes.

Below are the most common mistakes made when tackling an aeration and overseeding project, with tips on how to recognize and avoid them.

Choosing the Wrong Equipment

In many ways, your results will only be as good as the equipment you use. One common example is attempting to avoid buying or renting an aeration machine to prepare your lawn and going with a spike aerator vs a plug aerator.

Cheap alternatives include using a pitchfork (could work for small areas) or buying cleats with spikes on the bottom of them (like these ones on Amazon).

Neither of these options does the job well, and could even make the soil worse by compacting your soil further.

Do yourself a favor and rent a core aerator for 4 hours or for a day. It’s less than $100 and it’s money well spent.

Using the Aeration Machine Incorrectly

Even if you choose the correct aeration machine, you may still not be able to operate it properly.

Your whole aeration and overseeding adventure will be over rather quickly unless you get familiar with the equipment you want to use.

The most common type of aeration machine is a walk-behind, which may seem simple enough. However, because they are heavy to push you could end up missing some parts of the turf, or ripping apart your lawn when turning the machine.

Pay attention when picking up the equipment and ask questions of the pro you’re renting it from. Watch some online videos beforehand, and take the first pass with the machine over a part of your lawn that is the least visible from the street in case you make a mistake.

Picking the Wrong Time of Year

We have already covered the best time of the year to aerate and overseed your lawn, but some people will still do this project at the wrong time of year and be disappointed with the results.

It can be hard to wait when you’re ready to tackle a big lawn renovation, but don’t waste your time and investment because you were impatient. Your lawn isn’t going anywhere.

Harsh winters and hot summers will cause problems for seed growth if you overseed later than you should in the fall or spring.

Furthermore, you should avoid aerating soil when it is too dry because it will be harder for the machine to break through and the plugs won’t come out of the tines cleanly.

Ignoring the Lawn After Aeration and Overseeding

This seems like a no brainer, but you’d be surprised how many people go through the task of aerating and overseeding and then simply don’t follow-through with watering their lawn in the weeks following.

Unfortunately, those seeds you planted are not magical. They won’t grow overnight, and they won’t grow without consistent water.

The good news is simply ensuring the soil covering the seeds is kept moist is a good start for driving growth. If you do that and nothing else, you’ll probably get good results.

Rushing to Mow

One of the most common mistakes when laying seed is to think normal lawn mowing can resume right away. This is especially true when overseeding, because your existing grass will keep growing (and may grow faster with the extra water).

Some people make the mistake of continuing to mow their lawn weekly or more frequently and become confused when they didn’t get the results they hoped for when overseeding.

This happens because the seeds need time to develop roots that are strong enough to withstand the force of the mower’s blade. Mow too early and the mower will just rip your young seedlings out of the soil and kill them.

I usually recommend that you avoid mowing the lawn for 2 to 4 weeks after overseeding. You want your seedlings (not your existing grass) to reach at least 3 inches in height. You should mow at about 2.5 inches at that time, bagging your clippings.

This will stimulate growth of the new seedlings, and set you up for success.

Going After Weeds

Weeds are a problem and can cause a lot of damage to your lawn. At some point, weed mitigation needs to be at the top of your to-do list. But that time is not right after aerating and overseeding.

Whether you use chemical weed killers on your lawn or organic solutions, weed management can damage growing seeds and new grass. It takes some time after overseeding before you can tackle weeds again, usually around 4 or 5 mows.

Pulling the occasional weed by hand should still be okay. But just live with any new weeds that grow during the days when your new grass is young and vulnerable. You can address those problem areas later.

Choosing the Wrong Seed

Choosing the correct seed for your lawn is an art form. If you don’t have the gift (or are simply tired of reading online reviews where half the people suggest it’s the perfect seed and half the people suggest it’s the worst seed on earth), read my guide on choosing the best grass seed for overseeding.

If you can stretch your budget to a premium grass seed option, you’re more likely to get a younger and healthier seed. Shopping at a box store may be convenient, but a lot of that seed has been sitting there for years.

Not Following Seeding Rate

When you buy seeds, the packet will tell you the seeding rate. This is a requirement and not a recommendation that helps you understand how much seed your lawn needs.

By following the guidelines, you can ensure an even spread that allows the seeds to grow in a healthy way.

As I mentioned earlier in this article, I usually apply about 1.25 x the recommended overseeding rate because I love a really dense lawn. I also use an online tool to measure my lawn square footage and get the seed quantity correct for my lawn.

But following the manufacturer’s recommendation will usually give you a good result.

Additional Resources

• Should You Aerate Your Lawn? by Tom Kalb, Yard & Garden Report, NDSU North Dakota State University (link)
• Overseeding a Lawn by Richard Jauron, Horticulture and Home Pest News, Iowa State University Extension and Outreach (link)
• Lawn Aeration and Overseeding, College of Illinois Urbana-Champaign, College of Agricultural, Consumer & Environmental Sciences Illinois Extension (link)