Answer: When plant leaves get wet late in the day and stay wet overnight, they are more likely to develop diseases. Overhead sprinklers can still be used, though. Just water gardens early enough in the day so the leaves, flowers, and vegetables have a chance to dry off before nightfall. Early-morning watering is usually best, anyway, because there's less demand on the water supply and water pressure is higher. Also, early-morning drinks can prepare your plants for the long, hot day ahead.
In general, I suggest the use of drip or leaky pipe irrigation systems because they don't waste water. They apply moisture at the plants' roots, right where they can use it, and less moisture is lost to evaporation. They also help reduce excess moisture on the leaves, so they help reduce disease problems.
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