Originally Posted by Landscape Poet
On SA , FL landscapes recommended to me only one direction/pass. I would say this is very solid advice for SA as it does put it under stress with just one direction. I would assume two directions would result in turf loss in many circumstances.
Below is an article from the university of Florida, among other thing note they say verticut in a north south OR east west direction
Thatch is the layer of undecomposed leaf blades, stolons, roots, and crowns intermingled with soil (Figure 14). Leaving mowing clippings on the lawn does not cause thatch because clippings are readily broken down by microbes in the soil. Thatch development is greatest in grass that is overfertilized or overwatered. An excessive thatch layer reduces water penetration and can bind up fertilizer or pesticides. In severe cases, roots may be seen actually growing aboveground and rooting into the thatch layer. This is a very unhealthy condition and leaves the lawn vulnerable to many stresses.
Figure 14.* Thatch layers can develop in St. Augustinegrass, especially when fertilization or irrigation rates are high.
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If the thatch layer exceeds 1 inch, it may be removed by vertical mowing, or "verticutting," in early spring to midsummer. Verticutting uses vertical blades that slice through the thatch and slightly into the soil, resulting in much of the dead material being removed from the top of the lawn. A 3-inch spacing between the dethatching blades is best for St. Augustinegrass. Caution: Vertical mowing may result in damaged turf that requires a period of recuperation. Do not attempt vertical mowing unless the grass is actively growing. Verticut should be done in an east to west or north to south pattern, but not in all four directions. Debris should be removed by raking, sweeping, or vacuuming, followed by a conventional mowing to improve turf appearance and immediate irrigation to prevent root zone dehydration. One week after vertical mowing, fertilizer should be applied at the rate of 1 pound of nitrogen per 1000 square feet to encourage recovery. This material must be watered into the soil immediately following application to prevent plant burn. Periodic topdressing (adding a uniform layer of soil on top of the grass) with ¼ inch of soil similar to that underlying the turf is the best method to alleviate thatch accumulation; however, the physical labor required limits the practicality of this method for most homeowners. If topdressing, be sure to use soil that is free of weed seeds and nematodes and be careful not to exceed recommended topdressing rates, as this encourages large (brown) patch disease.