When beginning a lawn restoration, the first step is to remove any thatch buildup—even low levels are unacceptable. Unless you can expose the soil between the old grass plants, the steps that follow will have poor results. While you're at it, make a note of weed colonies and remove the worst of them with a grape (grubbing) hoe before proceeding to Step 2.
The best time to dethatch is when your lawn is thriving, not when it's stressed in the heat of summer or cold of winter.To begin, set the height adjustment on your mower to cut the grass about 1 inch high, essentially half its normal mowing height. Short grass will make dethatching and surface preparation easier. It will also improve seed germination rates because more seed will make contact with the soil, and seedlings will have greater exposure to the sun.
The easiest way to remove thatch from a lawn that is over 3,000 square feet is with a power rake, or vertical mower (a machine with vertical instead of horizontal cutting blades), which is available to rent. For smaller lawns or lawns with thin, 1/2- to 1-inch layers of thatch, a manual thatching rake will do a satisfactory job. When using a vertical mower to remove average amounts of thatch and to scarify the soil, set the blades to cut 1/8 to 1/4 inch into the soil. Make several test passes on an inconspicuous area of the lawn to judge how much thatch (and turf) will be removed. If too much or too little is removed, raise or lower the blades accordingly.
The spacing between blades can be adjusted on some machines, but this is difficult to do and so is best done by the rental store staff. The blade spacing for Bermuda grass and zoysia grass is 1 to 2 inches, while the spacing for bahia grass and St. Augustine grass is 3 inches. Most rental store staff will know the optimum settings for the grasses grown in your area.
When using a vertical mower to dethatch, make several passes over the lawn in perpendicular directions to ensure a thorough job. Remove the thatch you pull up after each series of passes and add it to your compost pile. When you have finished dethatching, remow your lawn to a height of 1 inch.
With a lawn that has thick thatch (more than 1 1/2 inches), you may need to partially remove the thatch and allow the lawn to fully recover before the next dethatching session. Removing too much thatch all at once can do more harm than good. The rule of thumb is to remove what you can without tearing up holes of more than a couple of square inches in live turf. This may not be possible with lawns that have very thick thatch, say, more than 2 inches. In that case, your lawn may not be salvageable and may need to be replanted from scratch.
More about lawn restoration:
Get Pre-Screened Lawn Fertilization and Treatment Help in Your Area
Get a Lawn Sprinkler Installation Contractor
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Courtesy Yardcare.com