How to keep olive trees healthy
We have two old olive trees (40 years old) and they were healthier during the first 20 years, and now they look kind of sickly and full of dead branches (that I constantly clean out) and not healthy. I would like them to be green and full of new growth. They are in San Diego. I heard there is a disease or something that attacked all of them in the neighborhood, but I don't know any specifics. Is there anything we can do? Fertilizer?