The best time to water is in the early morning hours. Plants use the least amount of water at night and the most during the day. Also, plants photosynthesize at night and need air to do so. The other problems with watering at night are that fungi get started because of the water sitting on the plant and the surface, thereby creating the perfect environment for slugs and other pests. When you water, water deeply and less frequently. You must soak down to the root zone. For new shrub plantings, soak thoroughly once or twice a week. If you are soaking deeply enough, you don't need to water every day. The best way to check is to either dig down after watering to see just how far down the wet soil goes or, use a water meter.