Early Leaf Drop (October) in Modesto Ash

Q. My 18 year old Modesto ash tree has been dropping green leaves for maybe 2 months now.  Unlike my other 2 Modesto ash trees that had entire branches die last summer and the dead leaves wouldn't even blow off. Any ideas?

Limb dieback for unknown reasons in Modesto ash

A. There could be a number of reasons for early leaf drop off but if your tree seems healthy and has been growing well then I would ignore it. Just make sure that it is getting deeply watered if it is in a rock landscape. Fertilize it once in January or February; there is no need to fertilize it more than that.

Probably the biggest problem is putting ash trees in rock landscapes. Modesto ash has problems of its own here in our valley so you may experience limb dieback at some point in its life. I do not recommend it for our valley anymore because of this.

Large ash tree in a lawn. You must overwater the lawn
so that large trees like these get enough water.

Also remember that as ash trees get larger they require more water. The amount of water required is not a simple doubling of the amount as the tree doubles in size. For trees, the amount of water the required is much more complicated than a lawn.