The ideal climate for an olive tree is the warm wet winters and hot dry summers of the Mediterranean. In the United States, the best places to grow olive trees are parts of California, Texas, Arizona and Florida. Too much humidity will hurt the plant, as will freezing winters. Caring for an olive tree takes little effort in the right climate--a little pruning, some fertilizer and a good watering once in a while during the dry season should be all you need.
Prune in early spring; use a pair of sharp clean shears to prevent transmitting disease to your tree.
Take off any suckers that are growing out of the trunk. Suckers look unsightly and can undermine the health of the tree by diverting growth.
Remove any dead wood you can find, you may need to use a tree saw for larger branches.
Remove any branches that are crossing another branch or growing downward. Olive trees should be open and airy; left unpruned they tend to get gnarled and twisted.
Look straight up though the canopy--if light does not filter though a part of the tree thin that part until it does. This will keep the canopy open and help fruit production.
Water your olive tree deeply once a month. Use a soaker setting on a hose and let the water seep into the ground for several hours; for a large tree you might have to let the hose run most of the day.
Fertilize using ground-up seaweed or a seaweed-based fertilizer to keep plants happy. Apply once a month or so. Olive trees are light feeders; if your olive tree looks unwell, it is more likely water deficiency than a lack of fertilizer.
Prevent water from sitting around the roots of an olive tree. This might mean creating a raised bed or mound before planting if you have heavy wet soil. If water sits around the roots of the tree it can cause root rot, which will kill the plant.
Protect your olive tree from heavy winds; if the tree is planted in a windy spot consider putting up a barrier to protect it. Olives are shallow rooted--with a full load of fruit, a high wind can uproot the tree.
Harvest olives gently, as the fruit is delicate and bruises easily. Pluck the olives from the stem and place them carefully in a picking basket.