There's so much more to a great yard than just mowing the lawn.

Core Aeration

One of the best things you can do to keep your lawn thick, healthy and green is to core aerate it at least once a year.

Why should you core aerate? Core aeration helps by punching holes in compacted soil and thatch. The machine then pulls out a core and deposits it on the surface of the lawn. The benefit of aeration is that it allows water and air to move deeper into the soil so the roots can grow deeper. When roots grow deeper, the grass grows taller and thicker.

If you don’t core aerate your lawn, you will notice two things.

Aeration CoresFirst, you will notice that over a period of years, you grass will become shorter and thinner, like it’s not growing vigorously. This is because the top 3 inches of soil compacts over time from walking on the grass, raindrops and droplets from your sprinklers and mowing. When the soil compacts, it doesn’t allow air and water to penetrate the soil, and the result is roots that cannot grow deeply.

Second, you may notice is the thatch layer getting thicker. If the thatch layer gets too thick, the roots of the grass will start growing in the thatch rather than the soil. The thatch layer is not a good place for roots to grow.


It’s best to core aerate during the grass’s peak growth period. For cool season grasses like Kentucky bluegrass, that is late summer or early fall, which is generally the last week in August until mid-October in Colorado’s Front Range. You want to aerate at least 50 days before the ground freezes so the grass has time to recover. In most years, the ground freezes sometime in December.

Aeration core closeupIn some situations, it’s beneficial to aerate again in spring. If your grass is showing signs of thinning or if it’s not growing very tall, or if you didn’t aerate in the fall, it’s probably worth aerating in the spring. In our area that would be mid-April through May. It’s best not to aerate during the heat of summer when the grass is stressed. In normal years, the weather usually starts getting hot in early to mid June, so make sure you aerate before then.

Hire someone or DIY?

You can rent a core aerator and do it yourself, or you can hire a landscape contractor or lawn service to do it for you. This isn’t really a difficult task, so feel free to give it a try, but keep in mind that the machines are pretty heavy and they bounce around quite a bit, so you do need to have some physical strength in your upper body to be able to do it by yourself.

Sometimes you can find a professional to aerate your yard for about the same price as renting the machine. One way to reduce the cost is to go in with a few neighbors to rent a machine and do all of your yards in the same block of time.

Preparing to aerate

Before you plan to aerate, make sure you water the grass well 24-48 hours before the time it will be aerated. This will soften the soil and allow the machine to pull deeper plugs.Use flags to mark all of your sprinkler heads so you can avoid damaging the sprinkler system.

Get good coverage

Aerated LawnCore aeration machines have tines that pull cores out of the soil and deposit them on the soil surface. They are usually spaced 2-4 inches apart. The deeper the core they can pull from the soil, the better. To make you get good coverage, make two passes across the lawn with the second pass at a right angle to the first.


What should you do with the cores?

After the lawn is aerated, you should notice a lot of cores on the surface. It’s good to have a lot of cores. What should you do with the cores? The best option is to let them dry out for a couple of days and go over them with a mower to break them up. This allows some of the soil and microorganisms fall back into the lawn, which will help break down the thatch layer. Feel free to rake any remaining pieces of cores left after mowing and throw them in your compost pile.

After you core aerate it’s a great time to overseed, if needed.

What about the hand tools or power raking?

There are some machines and hand tools on the market that punch holes without removing a core. These are the least effective since they just push the soil compaction deeper in the soil.

You may hear some people recommend power raking rather than core aerating. I recommend avoiding power raking. It is much harder on the grass and also leaves you with a disposal problem since these machine remove all the thatch. Core aeration is the way to go.

So to recap, core aerate your lawn at least once in late summer to early fall. If you have thinning or short grass or heavy clay soil, consider also aerating again in later spring to early summer. Let the cores dry out, mow over them, rake and dispose of any remaining material in the compost pile. You’ll have a thick green lawn as a result.

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