Mowing the lawn properly is very important for a healthy St. Augustine lawn. The biggest mistake that people commonly make is mowing too short! The thinking is that perhaps it won't grow as fast if it is mowed short. Or perhaps the property owner would just prefer the manicured appearance of a golf course. This simply is not possible with most St. Augustine turf.
Mowing the lawn too short causes a number of problems. It causes a stunted root system. Stunted roots won't allow adequate water or nutrient uptake. The grass will suffer from drought and deficiencies more easily.
Grass that is cut too short cannot adequately compete with weeds. Grass that is consistently cut too short will eventually decline and become weed infested.
There are some varieties of St. Augustine grass that tolerate a lower mowing height and will do well. These include Seville, Del Mar and Palmetto varieties. These grasses can be mowed at 3 inches high. However most lawns in the central Florida area are the Floratam and similar varieties. Floratam needs to be mowed at a height of approximately 3 1/2 to 4 inches.
For the typical lawn mower, four inches is usually the highest setting that the mowing height can be set on. This is usually your rule of thumb. Set the mowing height as high as it can be set on your lawn mower. Mowing at this higher level will also produce a more attractive lawn. When mowed too short the grass is being cut into the stalk. The stalk will not cut as cleanly as the grass blades. It also creates a ragged appearance which usually takes a few days for the grass to recover from. A properly mowed lawn will look excellent immediately after it is mowed if the blade is sharp.
Lawn mower blades must be sharpened periodically. A dull blade will rip and tear the grass blades resulting in a rough appearance to the grass. This also puts the grass under additional stress making it more susceptible to damage.
It is also important that string trimmers are not used to mow sections of the lawn. String trimmers have no height setting capabilities and can scalp the grass. String trimmers also cut very poorly, again ripping the grass blades.
The grass needs to be cut frequently enough also. Ideally you should not cut more than 1/3 of the grass height at any one time. So if the grass is normally mowed at four inches it should not exceed six inches in height before it is mowed again.