We have an established lawn here in northeastern Illinois (sodded in front, seeded in back) all planted 12 years ago. How often should we aerate it?

I have seen some people recommend doing this annually.

Others describe "the screwdriver test" to check for compaction: If you can push a screwdriver into the ground easily then the soil is not compacted and (so these folks say) does not need aeration.

I'm curious to hear your opinion. Thanks.

Lawn aeration is a great way to allow more air and water into the soil profile along with relieving soil compaction. The current thought on compaction is that a sodded yard seems to require core aeration more often than a yard that was seeded. Heavier soils that can compact easier may also influence how often aeration is done. If you core along with adding high quality organic compost as a topdressing material, the long term health of the lawn improve even more. For more information on lawn care you can visit http://urbanext.illinois.edu/lawntalk/

I understand the benefits of core aeration. My question is how to tell when it's needed.

Is the "screwdriver test" valid?

I like the idea of a test that assesses the lawn rather than going on a fixed schedule, because as you point out different lawns will be compacted to different degrees. I am looking for a test I can do myself because - let's face it - a company that does core aeration has a vested interest in advising me to aerate whether the lawn really needs it or not.

Thanks.

There is a specific instrument used to determine soil compaction used in soil science research that is very accurate and takes many of variables out of the equation so the results are reliable and repeatable. Using a screwdriver or some other kind of rod will give a “seat of the pants” result, which can help us decide if core aeration is appropriate. Be as deliberate and consistent as possible when you do this. The same soil when moist will allow the probe to enter the soil to a different depth than that same soil when dry for example. Try to use the same amount of downward force each time. Soil type, percent organic matter, diameter of the probe, downward force excerted each time are other examples. Visually if you examine the soil profile and see that the grass roots are not thriving and growing down 6-8 inches, everything else being equal, and if you have a difficult time pushing down past 2-3 inches and then easier again after that, then this is indicating a compacted layer. I have not ever heard of or seen a lawn that is harmed by core aeration that has a soil that is not compacted.

Thanks for the thorough response, Richard. It's really helpful.

I realize that me wielding a screwdriver is no substitute for a real pro assessing my lawn, but as you say a "seat-of-the-pants" test I can do myself is reassuring.

My concern is not damage to the lawn from overly-frequent aeration...it's damage to my wallet! Obviously I don't want to under-aerate either.

Thanks again.