St. Augustine grass needs to be cut at 3.5 - 4 inches high year around. With most push mowers and lawn tractors purchased from department or hardware stores...it will be the highest setting available. As the picture above indicates, consistently mowing at a taller height helps to reduce weed invasion and builds strong, deep root systems making your lawn more resilient to insects or disease...thereby reducing the need for chemical inputs. Keeping a sharp blade on your mower is very important also, and should never be under estimated or neglected. Sharpen your blades at least once each growing season and your lawn will love you for it!