A discussion has been going on lately under - Oak Tree Latest: Alesig, Today at 5:00 PM Pacific Northwest Native Plants Some comments have raised questions for me that don't really have anything to do with the question @Alesig was asking about leaf problems on his oak tree. So I thought a separate thread would be a good idea. I 'd like to know more about watering large trees. From what I've read, many large trees, like oaks, grow long tap roots to access water deep underground. Some sites say that trees grow most of their roots within the top 18 inches of soil and derive most water in that zone. How much does artificial watering help in the long run? It's obvious when you see boulevard trees languishing that the water bags placed by their trunks must do at least some good helping them survive. I wonder though about their long-term survival. What I notice here in the very dry area where I live is that young trees may grow happily for many years but eventually their water needs exceed what is available naturally. This is becoming ever more evident as the climate changes.