Core aeration and overseeding is one of the best ways to repair your lawn if it’s showing sings of weakness. Even if your lawn doesn’t require overseeding, it’s beneficial to add core aeration to your lawn care program.
What is Core Aeration
Aeration is simply the introduction of air into a material. In core aeration, you are introducing air into the soil of your lawn, using a machine called a core aerator. The core aerator works by having several hollow metal tines simultaneously dig into your lawn, removing sections of soil. These sections of soil are called plugs and they remain on the surface of your lawn until they naturally get broken down.
Benefits of Core Aeration
1. Breaks down thatch. A layer of thatch can suffocate your lawn.
2. Reduces soil compaction which allows roots to grow deeper.
3. Provides air to the root system of your lawn which makes healthier roots.
4. Allows fertilizer and water to access root zone easier.
5. When combined with overseeding it makes for optimal conditions to grow seed.
The seed can get into the voids left behind from the aerator and this makes for good seed to soil contact.
If you were to just overseed your lawn without core aerating, most of the seed would stay on the surface of your lawn. It has a greater chance of drying out and dyeing before it has a chance to germinate.
When Is Best Time to Core Aerate and Overseed Your Lawn?
For cool season grasses:
If overseeding, then late summer/early fall is the best time. At this point in the season a lot of annual weeds such as crabgrass are starting to die back and soil temps are ideal for seed germination.
If you wait until mid fall, there’s a good chance a lot of seed won’t germinate due to cooler soil temps.
Cool season grasses germinate best when soil temps are between 50 and 60 degrees Fahrenheit. But you want to get your seed down before that because soil temps drop quickly in the fall, and seed can take awhile to germinate. When soil temps drop down to 70 degrees towards the end of summer, it’s a good time to pull the trigger on core aeration and overseeding.
To get data of when soil temps in your region are in the 70 degree range check out Green Cast Online.
When using Green Cast for soil temp data, enter your zip code and look at the 24 hour average. If 24 hour average temps are 70 degrees or lower, it’s a good indication it’s time to core aerate and overseed. The other factor worth considering is the 5 day forecast. If you’re getting unexpected extreme heat, then wait until temps cool back down.
If just core aerating your lawn then you don’t have to worry about seed germination so you can do that later in the season.
For warm season grasses:
Late Spring/ Early Summer is the best time to aerate since this is when warm season grasses are actively growing.
Since warm season grasses spread via rhizomes and or stolons, there really isn’t a need to overseed after aeration. Their spreading nature fills in the voids left behind from core aeration. However, if you are doing more of a lawn renovation then you can seed right after core aerating.
Another overseeding strategy people use with warm season grasses is to overseed with an annual rye grass in the fall when warm season grass starts to enter dormancy. This will give you green grass during the winter months while warm season grasses are dormant.
This is a strategy you commonly see in golf courses down south. The annual rye thrives in the winter months and dies back with the return of the heat and warm season grasses coming out of winter dormancy.
If overseeding with annual rye, wait until fall when soil temps are cooling down and warm season grasses are starting to head into dormancy.
How to Core Aerate and Overseed Your Lawn
1. Mow Your Lawn
Before core aerating and overseeding make sure you mow your lawn short. This will allow the core aerator to dig into the soil better and pull out deeper cores.
When core aerating, you want your lawns soil to be moist so the core aerator can easily penetrate the soil and remove a solid core.
Aerate your lawn twice if possible, going in perpendicular directions. Set your core aerator to the deepest setting. Don’t be afraid to get a quick lesson at the rental yard if you are renting a machine.
4. Apply Seed
If applying seed, immediately after core aeration is the time to do it. Follow the overseeding rates on the back of the bag of fertilizer. You don’t want to overseed too heavily!
5. Apply Slow Release Fertilizer
Applying fertilizer is ok immediately after overseeding but you want it to be a slow release fertilizer such as Milorganite 6-4-0. If you use a quick release fertilizer the surrounding grass will have a growth spurt and it will shade out the seed and require you to mow more often.
Irrigate immediately after core aeration and overseeding if possible. Otherwise, do your best to schedule aeration and overseeding right before a light rain is forecasted.
Mow your lawn as needed over the next weeks as your seed germinates but be careful. Only go over the lawn once and try to avoid turning sharply. You want to do what you can to be gentle as your new seed germinates. Your seed needs sunlight to germinate so don’t make the mistake a lot of people make and stop mowing while you wait for seeds to germinate.
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