ummmm it is winter deciduous!

Here is a link that might be useful: Sambucus mexicana

There are a number of sources that refer to it as summer deciduous. As an example:

http://polyland.calpoly.edu/overview/archives/derome/scrub.html

Sounds like it was drought stress to me. Here in northern California it grows in stream side habitats and is most definitely winter deciduous,so ought to enjoy summer irrigation and stay well leafed with more soil moisture. Perhaps you are confusing it with Aesculus californica which will go into early midsummer dormancy when growing away from riparian habitats, and even when well watered will still be the first tree to drop its leaves, as well as being the earliest to leaf out with winter rains.

I checked Munz and he states that it is often quite deciduous in summer.
Bahia is right as its loss of leaves in summer is not what is generally considered to be a deciduous nature but a stress reaction. Other plants may not only loose leaves but entire branches when water stressed out.

I live among quite a few native Sambucus in Temecula. A large majority of them do not grow in riparian habitats and most have lost leaves due to drought stress. I have been watering one of them near a fence but it really doesn't seem to make a difference. It lost most of the flower buds and did not produce any berries. Maybe a long soaking would help yours. Where did you purchase it?

Ah, Tressa, your post solves the problem. I watered my elderberry quite regularly through the summer, so much so that when it started losing its leaves I wondered if I was killing it due to over watering. So I stopped. The tree stabilized with about 1/3 of its normal leaf load. I've not watered it since. Scrapiing the bark shows healthy tissue, and there are buds in leaf axils waiting for next season.

My tree is simply "programmed" to reduce its leaves in late summer, as your observations confirm. Its first two years it grew throughout the summer with plenty of water, not unusual, I have found, with some natives. Next year, I'll lay off the water by midsummer and let the tree do its things. RB

Interesting, they are evergreen here in Camarillo, even without irrigation. I suspect the reason it stayed evergreen the first two years for you is related to the proportion of new growth to the overall size of the plant. Of course, whether that is in turn related to the ratio of root hairs to the overall plant (and thus a product of physiological drought) or the role of photorespiration in nitrate assimilation - I'm not qualified to opine.

Ryan

They are also more likely to stay evergreen and actively growing closet to the coast where heat and drought evapo-transpiration rates are lower. I haven't noticed a tendency towards summer dormancy near San Francisco Bay, where evapo-transpiration rates are drastically lower than inland southern California. Location, soil type and local climate will all impact how this species behaves.

I would be interested in one or two Sambucus mexicana. Is there a reliable and affordable source of the variety or someone have good rootstock to share? Thanks.