Once you've determined that your lawn is in need of dethatching, here are a few tips to give you an idea of what is involved. Care must be taken not to try and remove all thatch from a lawn at one time. This will probably cause more harm than good and may actually kill the grass. Unless the lawn has extremely heavy thatch buildup, regular aeration treatments would be better.
Don't fertilize the lawn for at least 45 days prior to dethatching.
If you are planning to apply preemergence herbicides, do so after dethatching. Otherwise, the herbicides may bind with the thatch and decrease their effectiveness.
For best results, it is better to dethatch after a light rain or absent that, you've watered the lawn. Avoid dethatching when the soil is saturated after heavy rainfall. The reason for this is that the dethatching equipment will pull the soil and tear at the roots instead of slicing and lifting the thatch.
Mow the lawn to the lowest recommended height for your particular grass. Bag the clippings.
Avoid machines with flexible rake-type tines and dethatchers that attach to your rotary mower blade. These cause more damage than benefits.
If you plan on using a power dethatcher, locate all buried cables (i.e. landscape lighting, cable tv, phone, electric, etc.) and underground sprinkler lines and sprinkler heads.
For small areas you can use a cavex rake. The tines are actually sharp blades and more effective than using a regular garden rake. Pull the rake across the lawn, bringing the thatch up to the soil surface. DO NOT OVER-DO THE MANUAL RAKING PROCESS.
When using a mechanical dethatcher, it is better to set it too high than it is to set it too low. Since you almost always have to go back over spots several time the blades can be lowered once you become accustomed to working with the machine.
Power rakes and vertical mowers available through rental shops are generally lightweight and low-powered. This will require several passes to bring up the thatch. Make the 2nd pass at right angles to the first pass.
A lot of debris will be generated. Remove this debris.
Fertilize the lawn with a regular fertilize (non-weed & feed).
Stars indicate the best time to dethatch a lawn based on type of grass.