I too have olives on my property. There are several that are more than twenty years old. Some have been planted more recently. I'm in far north California in zone 8 with the most Mediterranean climate I can imagine. There are five manzanillo and two sevillano trees to my knowledge. Some of the others I'm not sure exactly what they are. Some have never produced at all and are candidates for grafting, others are more prolific and reliable.
