Early morning is usually the best time to water, especially if you are using a sprinkler or other method that wets the foliage. Watering in the morning gives the leaves enough time to dry before night. And leaves that are dry overnight are less likely to suffer from fungal diseases, because most fungi need damp leaf surfaces to spread. Morning watering also makes more efficient use of the water. Wind speeds are usually lower in early morning, meaning that less water will be lost to evaporation. Hot, dry climates are an exception, however. Many gardeners in arid climates prefer evening watering, which raises the humidity level in the vegetable garden. A little extra humidity often enhances pollination of beans, tomatoes, and other vegetables that depend on good fruit set. Ideally, do most of your routine watering in the morning whenever possible, and switch to evening watering when your beans and tomatoes are holding a heavy set of blossoms.