Your mower is killing your lawn because you mow too low. A St Augustine lawn, to be sustainable (to survive, to be hardy, to thrive), must have a minimum canopy height of 4” to 5”.
How Mowing Too Low Happens
It’s all about the look. A freshly mowed lawn looks good because it is level. To make a lawn level, all the grass must be the same height which forces you to mow the lawn at or below the shortest grass in the lawn. At that setting, the entire lawn will be short but level. The shortest grass is the weakest, thinnest part of the lawn – so mowing as low as the shortest grass dooms the rest of the lawn to the same fate. In the short term (after mowing), the lawn is level and looks great. In the long term, a short level St Augustine lawn will be a weak, thin lawn.
Why It Happens
St Augustine lawns do not grow uniform. Some areas are wet, some dry, some shady, some sunny - causing the lawn to grow at different rates. This uneven growth makes for an uneven lawn. The cure is to level it with a mower – just mow the lawn as short as the shortest grass.
What is the Solution?
Although the lawn will grow at different rates, all the lawn will grow to a height of 4” to 5” – eventually. Once the shortest grass reaches 4” to 5”, mowing at that height – 4” to 5” - will create a smooth level lawn that looks great and is sustainable.
4” Lawn - How to Get There
Growing a lawn to a sustainable height or 4” to 5” tall can be done in two ways: 1) do not mow until the shortest part of the lawn is 4” to 5” tall or 2) set your mower to mow at 4” to 5” and mow on a regular schedule. Option 1 is the easiest – just let your lawn grow until the shortest part of the lawn is 4” to 5” tall. This may take months depending on the time of the year and the lawn will uneven with a lot of showy tall weeds. To mow the lawn, set your mower so the lawn is 4” to 5” tall (usually the highest setting) and mow the lawn.
For Option two, set your mower to mow at 4” to 5” tall and mow the lawn on your regular schedule. It will seem odd that portions of the lawn are not being cut and the lawn will look uneven. Do not despair, eventually, all the lawn will be 4” to 5” tall, level and sustainable.
A third option is to combine Option 1 &2 – when you can’t stand the look of the lawn, mow at 4” to 5” tall. This will keep the lawn more acceptable – not level but presentable - while the canopy reaches the 4” to 5”.
All three options require you to delay gratification and to suffer with an “uneven” lawn for a season or more. The upside is that once the lawn reaches the sustainable height of 4” to 5” tall, you will be rewarded with a better lawn - a lawn that is durable, hardy, greener, require less water and recover quicker from damage or stress.
Be Patient - Your Reward is a Better Lawn
The homeowner is most likely to delay gratification with the promise of a better lawn. Getting out of mowing the lawn and improving the lawn is a win/win for the homeowner.
The least likely to delay gratification is the professional. The professional knows that a level lawn looks best, and an uneven lawn will not. And they want the recognition and possibly more work from neighbors who see their “good” work. To raise the mower to the sustainable heights will mean the lawn will be uneven and reflect poorly on their work.
The solution is to set a measurable standard of the professional's work and avoid terms like “attractive” or “best appearance”. Here is a suggested standard: After mowing, the tallest part of the lawn must be 4” tall as measured from the soil surface to the tip of the leaf. You can reassure your mow guy this is what you want, and you understand that this may not be the best look after mowing. If the mow guy persists on mowing too low, refuse to pay for any mowing that does not achieve this minimum standard. Most professionals will quickly raise the mower to be paid.