Q: Some of the University of Florida publications on lawn grasses talk about vertical mowing. What is vertical mowing?

A: The typical lawn mowers used in the home landscape are called rotary as the blades move in a horizontal plane. Vertical mowers have blades which move in a vertical (up/down) plane. This type of mower can be used to remove thatch buildup in lawns. If the thatch layer exceeds 1 inch, it can be removed by vertical mowing, or “verticutting,” in early spring to midsummer. It is a messy process and it is difficult for most homeowners to perform properly.

Verticutting uses vertical blades which slice through the thatch and slightly into the soil, resulting in large portions of the dead material being removed from the top of the lawn. Usually the blades are spaced about three inches apart which works best for St. Augustinegrass. This type of mowing can cause severe damage to the grass and requires a period of recuperation therefore it is best done when the grass is actively growing. Verticutting should be done in one direction only – not in cross sections. Verticutting will pull out large amounts of grass and thatch which will require cleaning and removal.

It will be important to mow the grass directly after verticutting but be sure to mow at the highest height – never scalp or cut the lawn too short. Water the dethatched lawn immediately to avoid dehydration of any exposed roots. One week after vertical mowing, you can apply 15-0-15 fertilizer at the rate of 1 pound of nitrogen per 1000 square feet to encourage recovery. Water the fertilizer in immediately to prevent burning the grass. Periodic topdressing (adding a uniform layer of soil or sand on top of the grass) with ¼ inch of soil matching the current soil is the best method to alleviate thatch accumulation. If topdressing, be sure to use soil free of weed seeds and nematodes and be careful not to exceed recommended topdressing rates. Adding too much soil or organic matter will encourages large (brown) patch disease.

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