If your lawn doesn’t seem to be growing as well as it should, even though it’s being fed regularly, it may be because of either thick thatch or compacted soil. In both cases, the grass is suffering because air, water, and nutrients aren’t able to move freely into and through the soil, and are having trouble reaching the roots. If your lawn’s failure to thrive is due to compaction, you will want to aerate it. 
Lawn Aeration 

Lawn aeration, coring, and aerifying are different terms you might hear for the same procedure. A core aerator removes plugs of soil from your lawn, which helps loosen compacted soil and allows vital air, water, and nutrients to reach the roots.

The idea behind lawn aeration and overseeding are to strengthen your entire lawn. By filling in empty or bare spots with new grass, you do more than making your lawn look beautiful; you actually increase its resistance to pests. With a thick, lush and uniform bed of grass, it’s harder for weeds to take hold, which makes taking care of grass easier, too.

Aeration breaks up compacted soil so water and other life-giving lawn nutrients can reach roots easily. This has a huge effect on grass health and growth. In fact, even if your lawn is gorgeous and green all over, you should still aerate in the growing season to keep things that way.
Best Time to Aerate Lawn 

The ideal length of your lawn depends on your climate, but most experts agree you should keep your grass between 2 1/2 inches to three inches long, with the last cut of the season remaining the same. 

Aeration is best performed just before or during periods of high growth. However, not immediately preceding or during periods of stress to the lawn. For example, heat or drought. The type of grasses that make up your lawn will determine the best time of year to aerate.

If you’re working with cool-season grasses, including bluegrass, fescue, and ryegrass, aerating during the growth periods in the spring and fall is best. For warm-season grasses such as Bermudagrass, buffalograss, St. Augustine and zoysiagrass, aerate during warm times of the year, between late spring and early autumn. 

In the spring, wait until you’ve mowed the lawn a few times before aerating. Doing so ensures the lawn will grow fast enough to recover and take advantage of the increased pore space and air exchange at the root zone that aeration creates. Aeration should be performed early enough in the fall that the turf can recover before it needs to prepare for winter dormancy. 

Shortly after aeration, watering the lawn, applying fertilizers and weed killers, and overseeding may be useful to do in order to ensure the highest quality of growth.