Lawn Aeration - The word "aeration" means "to supply with air." Soil that has been broken down by having too much organic material on its surface or has been crushed down cannot properly feed the grass growing in it. Sort of like a plant that has become root bound, the grass cannot get sufficient nutrients from the ground. In order to repair this problem, we need to loosen up the soil preferably without disturbing the grass growing on top. The term for the unwanted organic material on the surface is called "thatch." The term for soil that has been crushed down is "soil compaction." Both conditions suffocate the grass growing within it and need to be repaired for a healthy lawn.
Thatch - Grass is healthier if it is free of thatch and compaction. Thatch is that layer of dead leaves, old dead grass, tiny sticks and other "woody" organic matter that accumulates between the soil surface and the living grass. If thatch buildup becomes more than a quarter to a half inch, it can lead to lawn disease, drought and insect infestation. Aeration removes some of this buildup, and allows air and moisture to penetrate the soil which increases the activity of microorganisms that help decompose the thatch layer and feed and strengthen the grass. You can also do well towards de-thatching by raking. Raking with a stiff rake will also help loosen tough thatch. For best results, it is suggested that you rake trouble areas in your lawn before aeration.
Soil Compaction is where the soil loses the tiny air spaces within it from objects on top of the soil repeatedly traveling over it such as foot traffic. Heavy winds or rain can also cause soil compaction. The air spaces in the soil not only contain air, but also contain moisture and organisms that keep the soil active. Worms help keep soil alive by moving around in the soil eating bacteria, fungi, protozoa and organic mater and leaving its poo behind to help fertilize and de-compact the soil. When worms come to a highly compacted area, they tend to move around the perimeter of it, because it is too hard to penetrate. So, an already soil compaction problem tends to stay a problem without aid from our little soil caretaker friends. Signs of soil compaction include rapid browning of vegetation in dry weather, foot or tire worn areas and poor drainage after a rain. Heavy soil compaction problems are best cured by core aeration. To test the level of soil compaction, spray the area in question with a garden hose. If the water stands and does not soak in quickly, the soil is compacted. You should be able to press a small stick such as a wooden match into the soil about an inch or so fairly easy.
When to Aerate - Depending on the variety of the grass, its requirements may vary, but it is safe to say that for the spring growing season, it's a good idea to give your grass a little breathing room. Some people say to aerate lawns in the late Fall and others say to do it in late Winter, early Spring, either way is fine, but I prefer to do it in early spring just before I put down my initial weed and feed.
Types of Aeration - There are basically two types of aeration methods. Spike aeration and Core aeration. Core aeration is sometimes called plug aeration because it leaves little chunks (plugs) of soil on the ground. It is safe to use spike aeration annually, but core aeration should only be done to correct soil compaction once every three or four years, and not as routine lawn care.
I have found that it is easy for me to do core aeration on or close to the 29th of February. This way I know I'm not over doing it, and because leap year is every four years, it makes it easy to remember too. I do spike aeration every year except when I core the lawn.
Aeration Equipment - What you need to aerate your lawn varies by the size and condition your lawn is in. If you have a small yard, you might get by with poking hole in the ground with a garden fork or some other sharp pointed hand/foot tool. If your lawn is larger or is more compacted, then a larger tool is needed. You can get powered walk-behind aerators and aerator attachments that hook up to most any riding mower or lawn tractor. You can either rent or own lawn aeration equipment. Keep in mind that this is at most an annual chore and aerators are not very small, so unless you are a lawn professional, it doesn't really make sense to own an aerator. Renting is probably the best way for you to aerate your lawn. You will need to pick an aerator that is powerful enough to get through heavily compacted soil. Rental prices vary, but it is typical to pay anywhere from $50 to $75 bucks a day for a nice aerator. You might find it cheaper and easier to hire a lawn professional with the right gear to do it for you.
Aerating Your Lawn - Before you start dragging out the aerator, you should first cut your lawn very short by lowering the mower deck to one of the lowest settings. Then run the aerator over the lawn taking care to not get too close to any tree roots that may lay on or close to the surface. If you are using a core aerator, take note that the machine will leave plugs all over the yard. Although it will look weird for a short while, leave the plugs on the yard so they will release their nutrients back into the soil. You can run your mower back over the lawn with the deck in the lower setting to breakup the plugs which will help them dissolve and make your lawn look a little better. After the grass starts growing it will hide the plugs that are left on the ground. I also found that watering in the early evening each day for the first week helps dissolve the plugs faster. Be sure to reset your mower deck back to its normal setting when you're done so you don't forget.
Caution - Be sure you locate your sprinkler system if you have one. The aerator can make a mess of a sprinkler head or PVC pipes that are buried too close to the surface.