That’s the thatch layer, and if it’s a relatively thin layer, you can leave it alone. If it’s less than a 1/2 inch, you should let it remain as it will act as a natural compost for your grass. However, if it’s thicker than 1/2 inch, you’ll need to remove the thatch to allow your lawn a chance to get more oxygen. You can use a thatch rake, or a regular rake if it’s heavy enough to do the job.
This kind of aerating is more labor intensive because you remove the soil to a depth of 2 to 3 inches below the ground surface. Core lasts longer, however, because it loosens the soil to a greater depth. Many people choose to leave the soil plugs on the lawn, as they disintegrate within a couple of weeks. If you prefer, you can rake them up and discard them, as well. Before you aerate the soil, you want to be sure to prepare the ground first. If you look carefully at your grass, you may see a layer of dead grass, leaves and dried roots.