New plantings should always, ALWAYS be watered in thoroughly!! You cannot rely on just rainfall to provide adequate hydration even if it were to come in measurable amounts :-)

Cooler temperatures will slow soil moisture evaporation but the plants still need to enter winter with proper hydration. I can't tell you how often to water as that will depend on weather, soil conditions and the plants themselves but the soil surrounding and to the full depth of the rootball should stay consistently moist....not too wet and not too dry. Physical testing by hand is the best way to judge.

Thanks for the quick reply. I’m getting out the hose right now!