For best quality landscapes, supplemental irrigation is almost always necessary during Kentucky summers. If you compare the long-term average rainfall for Kentucky (46 inches annually) and water requirements for growing turf and woody plants, you could easily conclude that lawns and woody plants do not need irrigation. On the other hand, if you consider the extreme variability in our rainfall and temperatures, your need for supplemental irrigation is obvious.
Powell, A. J. and Witt, Mary L., "Home Lawn Irrigation" (1987). Agriculture and Natural Resources Publications. Paper 37.