HI, Susan, Any time a plant drops all its leaves prematurely, it is a sure sign it is under stress. In your case (and not sure of what weather conditions are like for you in late summer), I would assume it is either lack of water or too hot. Given your altitude, I know there are some roses better suited to higher altitudes than others, but 'Lili Marleen' isn't noted as one of them. Kathy C
I have about 100 Lili Marleen roses planted at 3000ft altitude in France. They do well, in general, although often from late summer onwards they lose their leaves although still flower. Is there something I can do to prevent this? Thanks Susan