You may not need to water at all with 40 inches per year. Here's the general plan for watering that seems to work everywhere. It's based on air temperature, but on an island with higher humidity, it might need to be adjusted downward.

Watering: Deep and infrequent is the mantra for watering. This is for all turf grass all over the place. Deep means 1 inch all at one time. Put some cat food or tuna cans around the yard, and time how long it takes your sprinkler(s) to fill all the cans. Memorize that time. That will be the time you water from now on. My hose, sprinkler and water pressure takes 8 full hours to fill the cans. Your time will likely be less. I like gentle watering. As for watering frequency, that depends on the daytime air temperature. With temps in the 90s, deep water once per week. With temps in the 80s, deep water once every 2 weeks. With temps in the 70s, deep water once every 3 weeks. With temps below 70, deep water once a month. Note that you have to keep up with quickly changing temps in the spring and fall. This deep and infrequent schedule works in Phoenix and in Vermont, so it should work for you. The reason for deep and infrequent is to grow deeper, more drought resistant roots and to allow the soil to dry completely at the surface for several days before watering again. If it rains, reset your calendar to account for the rainfall.

dchall,

Thanks very much. I suspected the watering schedule set up by the landscaper when the lawn was put in may not be right now.

Linda

Usually the schedule set up by the landscaper was never the right schedule. They want to water 1/7-inch daily instead of 1 inch all at one time.

The best way to understand what is happening with your lawn is to get a soil test to see what types of nutrients your lawn is lacking or has an excess of. Here in Boca Raton, FL over-watering is a problem during certain seasons more often than not. I consistently recommend a fertilization plan that lines up with each season to strengthen the roots of your lawn. This not only improves the overall health of your lawn but it also allows the grass to recover more quickly from harsh weather that the various seasons bring. Check out some tips and tricks we employ!