Prune a mature tree to develop good secondary branches. You can also prune out stems with fruit, though this may remove too may leaves. However, if summers are dry and you cannot provide adequate water to the tree, prune some stems to reduce the number of leaves and thereby the competition of fruit and leaves for water. It's a good idea to sterilize your pruning tools between cuts, especially if there is any evidence of disease. Prune away frost damage in the early summer.
Olives ripen through the autumn and into the winter.
Their color changes as their oil content increases, and the color moves from green to violet to nearly black. At this time, the tree still requires water and nutrients. Green table olives are harvested first, often gathered unripe. Some of the olive tree varieties available in the United States are Sevillano, Ascolano, Barouni, Manzanillo, and Mission. Resistance to cold is a trait of some olive trees, so if you live in an area with marginal winter temperatures, look for a variety that's resistant.