Q: I have a question about your recent advice to water in the morning. It rains any time of the day or night but I’ve never seen any plant damage because of wet leaves in the evening. Dew also gathers on the leaves as the air cools. Perhaps you can provide more information to support your answer.
A: A key irrigation concept is to avoid extending the period leaves are wet. It’s true that rain and dew wet leaves. Dew forms each night when the dew point is reached. In summer, the dew point is around 65 degrees, which typically occurs between 4:00 and 6:30 a.m..
This means plant leaves are wet from around 4:00 a.m. until they dry off around 10:00 a.m. and are damp for six hours. On the other hand, if you water plants in the evening and they don’t have a chance to dry off, they might be wet for 12 – 14 hours.
Fungal and bacterial diseases can develop when leaves are wet for 8 – 12 hours. So the goal of irrigating lawns or landscape plants is this: to water at a time that results in the least likelihood of the leaves being wet for more than 8 hours. That’s why it’s better to water in the morning. Thanks for the opportunity to explain!