Oleanders Drop Leaves in Drought. Will it Recover?

Q. I read the post on your blog on oleanders with interest. I too have an issue. My five oleanders are mature (at least 20 years old) trees.  When we moved here a year ago they had not been watered.   When the water was turned on and major landscaping installed, many of the leaves turned yellow and dropped. However the trees blossomed and continued to do fine. 

This is not the readers oleander but this oleander has leaf
scorch and leaf drop while the oleander behind it is
doing very well. Check the emitters or the source of water.
This is a good sign it is getting a lack of water.

            During the rains the gardener turned off the water system and sadly forgot to turn it back on. The water is of course back on but I have had to replace many bushes, although NOT the oleanders.  However they have begun to turn yellow again and are dropping leaves. There are still a majority of green leaves and the trees are about to burst into blooms. They have been fertilized, as has everything on the property, but I am baffled.  Would you be so kind as to give me your advice on what is happening and why?

A. Oleanders are so extensive worldwide that no one is sure where they originated from. Their climate of origin is important because it determines under what conditions these plants perform best but we do know quite a bit about how oleanders behave with and without water.

            We know that they are very drought tolerant. This means that when there is limited water, they can survive. Many plants can’t do this. Normally when drought tolerant plants first experience a lack of water the leaves will drop and the canopy will become sparse. If the water continues to be sparse the leaves they produce will be few and smaller and little new growth. They have to have a sparse canopy to survive.

            However when water is present they have the potential for using a large amount of water and are not low water users. They respond to this water by growing more, setting new leaves that are quite a bit larger and shedding the old ones. The plant itself becomes denser and flowers profusely (provided they are not trimmed with a hedge shears).

            Leaf drop is very characteristic in response to a drought. It is also characteristic when they receive water again after a drought. It is also characteristic of older growth to shed some leaves on older wood.

            So, in a nutshell, going from drought to abundant water expect some leaf drop. And when oleander grows normally, expect some leaf drop as the plant matures but not typically as much as during dry/wet periods. So is oleander a good pool plant? No.