Aeration is an important step in keeping our lawns healthy as it enables easier deep penetration of water and nutrients into soil, and decompacts clay soil we generally have in Central Texas. However, this is also a deeply misunderstood topic (falsely advertised to be more precise), and in our experience, most homeowners hurt their lawns following the practices advocated by many generic lawn care websites.
Aeration is basically poking holes in your lawn so that water and nutrients have easier access to deeper soil. There are two main types of aeration, and one marketing trick:
Spike aeration - metal spikes are used to poke holes in your lawn, which opens up an easier path for water and nutrients to penetrate into your soil. No decompaction of soil occurs as you end up with the same amount of soil per sqft of lawn.
Core aeration - hollow spikes are used to pull soil cores (pieces of soil 3/8"-5/8" in diameter, and often 1.5"-3" in length) out of your lawn. This decompacts the soil as part of the original soil is removed from your lawn.
Liquid aeration - marketing gimmick/monstrosity promoted by some large lawn care chains. We will write a follow-up post on this, but as you can imagine, we are not huge fans. For now, if "liquid aeration" treatment contains surfactants, stay away from it; otherwise, go for it, but understand you are getting a soil amendment rather than aeration.
Timing of aeration is where we see homeowners make largest mistakes, and often aerate at exactly the worst possible time (during transition from dormancy). In the short term, aeration damages your lawn as you are poking holes in it (spike aeration), or removing pieces of lawn (core aeration), so timing is critical. In general, aeration should be done when lawn growth is strongest:
This is especially critical for core aeration where your grass roots, rhizomes, and stolons will be damaged. Unless your lawn is already extremely strong, do your core aeration in mid Spring, when it is growing fastest, and the Summer draughts haven't yet set in. Early Fall is also an option if you irrigated properly during Summer.
Spike aeration is less damaging to the lawn as fewer roots will be cut, and it can be done multiple times a year. We still advise to do it only during the active growing season, unless you have dead patches of grass; in that case you might consider spike aerating only the dead area of lawn in late Winter to make it easier for your healthy Bermuda/Zoysia to fill it in.
Pick up your core aeration cores/plugs. Some people argue for leaving them to return nutrients to the soil, but you are just returning back the same crappy soil that was there in the first place. If you want to add nutrients to the soil, get some fertilizer. If you don't pick cores up, they will stay on top of your lawn, creating shade, and damage the lawn in those tiny shaded spots. Also, the first time you run them over with your mower's wheel will "pancake" them on top of your lawn and create an even bigger mess that is almost impossible to clean up. At that point you can only wait for strong showers to eventually wash it off.
If you don't want to deal with irrigation repairs, mark your sprinkler heads and valve boxes. Smaller lawns might only have irrigation heads on the border of the lawn, but if you have unmarked irrigation heads in the middle of your lawn, you are just hoping for luck - they will be destroyed if they get hit by a spike from any type of aerator. Valve boxes can sometimes survive drum aerators, but reciprocating aerators will usually punch through them and often damage valve's solenoid - just mark them rather than dealing with potentially expensive repairs.
To summarize:
Core aerate once per year, when your lawn is strongest. You can be more liberal with spike aeration. Avoid liquid aeration unless you understand exactly which ingredients are in it.
Pick up your core aeration cores/plugs or you will be dealing with mess for a while.
Mark your sprinklers and valve boxes.