Pronounciation: O-LEY-a eur-oo-PAY-ee-a

Hardiness zones
Sunset 8, 9, 11-24
USDA 9-11 (arid and semi arid regions only)

Landscape Use: Olive is a tree for Mediterranean, xeric, or oasis design themes, residential, commercial, or industrial plantings, not a good shade tree, but sometimes used as a "parking lot shade tree" because it's so tough. Dwarf sterile cultivars are quite popular in Phoenix and are used as landscape subshrubs.

Form & Character: Naturally rounded and frumpy like some floppy shaggy dog, rugged, glaucous, Mediterranean.

Growth Habit: Evergreen, woody, perennial broadleaf multi-trunk tree, slow to moderate growth rate to 30- to 50-feet tall with near equal spread, profuse basal suckering is common. With age, olive trees will form a pronounced trunk flare.

Foliage/Texture: Small, elliptic to lanceolate leaves with prominent midvein, gray-green above to silver white underneath due to tomentose hairs, less than 2-inches long; medium-fine texture.

Flowers & Fruits: Male flowers yellow and in panicles, followed by smaller, greenish yellow female flowers, male flowers fragrant and allergenic; fruits are oblong, black to 1.5-inch long stains, must be leached to be edible, high oil content.

Seasonal Color: None

Temperature: Tolerant of cold to 15^oF, and boy, do olive trees love the desert summer heat!

Light: Full sun

Soil: Tolerant of alkaline soil.

Watering: Infrequent deep supplemental irrigations are all that's required.

Pruning: Olive trees as landscape ornamentals typically have high maintenance requirements because of our modern day 21^st century fetish with creating 'clean, organized, and highly structured' landscape spaces. In that light, pruning demands are many including removal of basal trunk suckers and water sprouts, crossing branches and misdirected limbs, crown raising and/or crown thinning. Crown thinning is best practiced in late February as one way of reducing the number of April flowers. Tree training requirements are especially high when olive trees are young. Sometimes tree pruning wizards (aka the 'Horticultural clods of Phoenix' or locally known as 'Hort clods') resort to shearing and create olive topiaries as a way of controlling these scruffy landscape trees. The end products are sometimes comical such as these landscape balloons, landscape toad stools, or the proverbial olive tree in a pot.

Propagation: Seed, cutting

Disease and Pests: Olive knot forms galls on twigs and branches, verticillium wilt, scale and spider mites.

Additional comments: Olive trees are easily transplanted. Many municipalities now require the planting of non-flowering forms due to the allergenic properties of the olive tree's male flowers and the surface staining of concrete and asphalt surfaces by smashed olive fruits. Olive trees in old northern Greek olive orchards have a picturesque trunk.

Some common, partially or fully sterile olive cultivars that grow few or no flowers or fruits include:

• 'Bonita' - only a few tiny fruits
• 'Little Ollie' (a mutated hybrid of Olea europaea or a hybrid of Olea verrucosa) - a highly popular dwarf cultivar that is used as a landscape subshrub.
• 'Majestic Beauty' - only a few tiny fruits
• 'Swan Hill' - fully sterile
• 'Wilsoni' - fully sterile

Healthy living: The health benefits of consuming olive oil as a regular part of one's diet are well documented. Olive trees are highly revered for fruit production within the United States, especially in the central Valley of California. In Europe, olive is primarily grown for oil extraction. Cultivars most commonly employed for fruit production include 'Manzanillo', 'Mission', 'Ascolano' and 'Sevilano'.

Special note about olive fruit control in Phoenix landscapes: There are two chemical spray methods used to control olive fruiting in urban landscapes. First, fruit control may be accomplished via spraying the trees with auxin-derivative compounds (like the brand name Olive Stop) that are applied at the time of flower bud development to abscise flowers before they can mature, produce allergenic pollen and fruit. For this the application timing is very critical for effective control. Second, anti-gibberellin growth retardants (like the brand name products Embark and Maintain) which act to slow or stop all plant growth and development are sprayed onto the tree sometime before flower initiation in the very early spring (February in Phoenix) to prevent flower development. Application timing with this method is less critical, therefore it is often preferred by busy landscape management professionals. However, the long-term effects of annual applications of these anti-gibberellin growth retardants as a strategy to stop flowering will eventually cause a decline in tree vigor, increased sensitivity to environmental stress, and eventual death. Also, spray drift of anti-gibberellin growth retardants onto adjacent landscape plantings will cause similar foliar and growth distortions to these plants if proper precautions are not taken. A third non-chemical strategy is to prune olive tree canopies in February effectively removing flowering wood. This strategy will only lessen, not eliminate, olive flower/fruit production, but is environmentally safe.