An aerator pulls plugs of soil out of a lawn. Actual cores, lifted out and dropped on the surface, where they break down over the following two or three weeks. That is different from a machine that only punches holes, which compresses the soil it displaces instead of removing it.
Ground on this side of the valley is heavy to start with, and a lawn that is mowed, watered and walked on all season packs down harder every year. Compacted soil sheds water rather than taking it in, and roots stop descending because there is nowhere to go. Pulling cores opens it back up, so water, air and fertilizer reach the root zone instead of running toward the gutter.
Timing is most of the result. Early fall is the window on a cool-season lawn, while the grass is building roots rather than blades. An aeration paired with a late-season feeding does more for a lawn than anything else on the calendar, and it is the reason some lawns here look better every year while the one next door looks worse.
These are walk-behind machines. They fit through a standard gate and work around trees, beds and sprinkler heads, which is what most residential properties actually require.
One thing worth knowing. Aerator tines will destroy a sprinkler head, and they will find shallow wire. Heads and lines get located before the machine starts. On properties where we installed or maintain the irrigation, we already know what is down there — which is a practical argument for having the same company do both.
Used for aeration, and usually scheduled alongside fertilization or a fall cleanup.