Dethatching Your LawnWhen it becomes clear that a deep raking or a simple aeration isn’t going to solve your thatch buildup, it’s time to undertake a real dethatching. But be aware that dethatching seriously stresses your lawn, chewing up your soil and damaging grass blades and crowns. Be careful not to do more harm than good.
Although you can dethatch with a special tool called a cavex rake, the process is fairly laborious when done by hand. It makes more sense—even for an average size yard—to rent a power dethatcher. These machines are usually called vertical mowers due to the orientation of their blades. They are extremely effective at digging out thick layers of thatch. They are also easy to use, and are similar in operation to a gas-powered lawn mower. You’ll find them in the lineup at most equipment rental outlets.
Perhaps the most important part of using a vertical mower is setting the blades to the proper cutting depth so they remove thatch without cutting too deep into your soil. Start with a setting between 1/8 and 1/4 inch, going deeper if needed to remove all the thatch.
The time that you select to remove the thatch is just as important as how you go about it. You should dethatch cool-season lawns in mid to late summer, right before they green up in fall. Warm-season lawns are best dethatched in late winter or early spring, before they start their summer growth spurt. The idea is to put the lawn through the trauma of dethatching right before it goes into a period of active growth, when it will best be able to recover. For the same reason, lightly fertilize and water thoroughly right after you finish dethatching.
If your thatch buildup is more than 1-1/2 inches, don’t remove all of it at once. Run the machine once each way and then wait until the lawn recovers before dethatching again. A few basic practices will ensure that you minimize the trauma of dethatching and help the lawn rebound effectively to grow even stronger after the process has been completed.
• Avoid feeding the lawn. If you’re planning on dethatching, don’t fertilize for at least two months before you do it. The same goes for treating the lawn with any kind of preemergence weedkiller. Wait until right after you’ve dethatched the lawn.
• Water the lawn lightly before dethatching, or dethatch it right after a light rain. The soil should be moist, but not sodden or bone dry.
• Mow low. Cut the lawn below the minimum of the recommend height for your species. Bag or rake all the clippings off the lawn.
• Always start power dethatching with the machine set high. You can then lower the blades to remove all the thatch after you become used to its operation.
• Water deeply as soon as you’re done.
A vertical mower (also called a power rake) makes quick work of the rigorous job of dethatching your lawn.
Use marking paint to mark all underground lines and cables, including utility, power, and gas lines, and television cables. Mark in-ground sprinkler lines and head locations.
Mow the lawn to about half the height you would normally mow it, bagging the clippings. Rake up any leaves and debris on the surface of the lawn.
Adjust the vertical mower to the correct depth for your grass (the rental store can advise you on how to do this). Make the first pass, and adjust the settings as necessary.
Warning 
For the most part, vertical mowers are easy to use because they are operated much like a walk-behind mower. But don’t let their similarity to mowers allow you to forget that they are dangerous power equipment capable of causing injury (as well as causing damage to your yard if used improperly). Always wear safety glasses, sturdy shoes or boots, and long pants. Don’t ever turn the unit on its side when it is running. If it binds up or catches debris, shut it off and then inspect under the deck.
• Be aware that there are many different blade designs for vertical mowers. When renting one, never leave the rental center until you are absolutely clear on how to adjust, change, or set the blades for the particular machine you’ll be using. The rental center pro should brief you on this and other safety issues.
Make the second pass at a 90° angle to the first, and alternate in this way until you’ve covered the entire lawn.
Rake up the waste left behind by the vertical mower. Compost this debris unless you have previously treated the lawn with chemicals.
Thinking Green 
You can avoid the use of a gas-guzzling machine by dethatching your lawn manually. All the process requires is a special implement called a cavex rake and lots of elbow grease (look at it as a chance to get some exercise while improving your lawn and the air quality). This rake is equipped with sharp, crescent-shaped blades. To use the rake, force it down and pull hard to cut smoothly through the thatch, removing it as you pull. Collect and compost the debris you remove after you’re done.
Cavex rakes are typically used on smaller plots of grass because they require a lot of effort, but regardless of where you use one, rake over a given area of grass only once. First-time users have a tendency to overuse with a cavex rake, which can stress the grass.
