Peering at sweltering turf from the confines of your comfortable home might make you want to give the green carpet a drink to get it through hot weather, but resist the temptation. Rapid evaporation makes watering in the middle of the day wasteful. The best time to water grass is in the early morning. Wind and heat are usually minimal at this time, and the majority of the water will reach the lawn. Plus, the grass leaves and stems will dry by midday, lessening the chance of disease.
If you must water during the middle of the day, the grass will not be harmed. Myths abound about burning the grass from sun rays concentrated in water droplets. That is a misconception. Many top-notch golf courses spritz their greens on hot days to reduce heat stress on the grass.