Water tomato plants every week during the growing season. Once established, tomato plants require 2 inches of water each week. For optimal growth, tomato plants also require at least six hours of sunlight daily.
Add a layer of mulch, and place large, flat rocks next to the base of each plant to retain moisture. The rocks keep water from evaporating so the ground stays hydrated. The best times of day to water are early morning and late afternoon. Avoid watering in the early afternoon due to excessive water evaporation. Also avoid night time watering because plants become overly damp and prone to disease.