Why Aerate?

Because it's a good idea, that's why.  Healthy grass roots need air and oxygen to grow.  And water, of course.  Unlike flowerbed soil, the soil under your lawn never gets worked, but instead becomes more compacted over time.  Compaction reduces oxygen and water availability.

Aeration removes plugs about three inches deep and four inches apart from the thatch and soil.  Air and water reach the roots more readily, and exposing the thatch to air means microorganisms can grow and decompose the thatch better.  Less water is lost to evaporation and runoff.  Aerating even helps with nightcrawler problems; those lumpy bumps of worm "castings" in your lawn have more below-ground spaces to fill instead of mounding on the surface.

Leaving the plugs on the ground is good for at least three reasons:  1- As they disintegrate, they help with thatch decomposition.  2- There's still fertilizer in the plugs.  3- If you pick them up, they weigh a ton, and you need a compost pile to put them on.  The landfill doesn't want your lawn, even in tiny pieces.  If the plugs are too unsightly, you can break 'em up with a lawnmower or the back of a rake.

A core-type aerator is the only kind that should be used.  Spike aerators and special aerator shoes or golf shoes don't work because they actually compact the soil around the holes.

Aeration can be done any time the ground's not frozen, but shouldn't be done in the hottest days of summer, or when the ground is soaked.

Pronunciation Guide:  We professionals, and those in the know, pronounce it "air-ate," not "airy-ate."

-Bob

p.s. Did you know that professional athletic fields and better golf courses are aerated monthly or even more frequently?  And that lawn fertilizing companies, when they accidentally damage a lawn, offer a free aeration?  That's about the first thing they do.  Smart!