The common evergreen olive belongs to the genus and species Olea europaea. It comes from the European and Middle Eastern regions near the Mediterranean Sea, and parts of Asia and Africa. Ancient residents of Crete and Syria cultivated olive trees as long ago as 2500 B.C. Commercially grown in California's Central Valley and near Phoenix, Arizona, olive trees need long, warm summers. Trees can reach 50 feet tall, so you might want to prune yours to make harvest easier and keep the tree a manageable size of about 20 feet tall.
Prune young trees to begin training them to the shape and size you want. Prune off suckers that grow from the base and all branches that are forming low on the trunk. Leave a strong central leader trunk and favour strong, evenly spaced branches. Use your loppers or garden clippers, depending on the size of the suckers and branches.
Cut lower branches of older trees during their winter dormant period. Also, cut branches that appear dead or diseased. Use loppers for smaller branches and a tree saw or chain saw for large branches. Cut branches on the branch side of their collar, which is a bulbous area where the branch grows from the trunk.
Cut branches that cross other branches to attain an attractive form. Use your loppers or saw and cut near the trunk, avoiding the collar.
Thin spindly branches and leave stronger branches. You can also make stiffening cuts of long, spindly branches by cutting off about one third of their length, which will force them to grow thicker and stronger. This method works well on the central leader as well.
Step back and evaluate the appearance of your tree. It should be globe-shaped, symmetrical and visually appealing. Prune additional branches to achieve the appearance you desire.
The University of Minnesota Extension website recommends making three to four cuts when you remove large branches. Just outside the branch collar, make a cut part way through the branch, from the underside. Then make one or two more cuts from the upper side, near your first cut. This practice will help to prevent tearing of the trunk. Consider hiring an arborist or tree-trimming service if your olive tree is very large.
Prevent injuries by wearing sturdy gloves and goggles to protect your eyes from flying debris. When cutting diseased tree parts, sterilise your cutting tool in a solution of bleach and water between cuts to prevent spreading the disease. Use one part bleach to nine parts water. Olive knot disease is common when you prune during rainy weather and fail to sterilise your cutting tools.