Olive

About Olive

The olive is a slow, long-lived evergreen tree with silvery leaves that handles heat, drought and poor soil. Most varieties crop better with a second variety nearby, and the fruit is too bitter to eat until it is cured. In a pot it makes a handsome porch tree that fruits best after hot summers. Heads-up: the California Invasive Plant Council rates olive as a 'Limited' invasive because birds spread seedlings into wild areas there.

NC State lists zones 8-10 (some cultivars 7); UF/IFAS says olives grow where winters stay above about 12 F. Cal-IPC rates olive 'Limited' (escaping in southern California and the Central Valley) and suggests fruitless types near open space; USDA PLANTS lists no noxious status.

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

In the ground, plant in spring after frost or in fall, 20-25 ft apart, with the root crown slightly high (UC Marin Master Gardeners). Potted trees go back outside once frost danger has passed (no source gives a set number of weeks, so the window is left blank). Grafted or cutting-grown trees start bearing in about four years (UF/IFAS).

Soil

Any well-drained soil, including poor soil, up to about pH 8.5; sandy soils are best because olives get root rot in wet ground (UF/IFAS; UC Marin Master Gardeners).

No rich soil needed: olives grow in almost any well-drained soil up to about pH 8.5 and bear poorly on very fertile ground (UF/IFAS).

Feeding

• Young in-ground trees, monthly in the growing season: nitrogen fertilizer such as urea or blood meal. UC Marin Master Gardeners use about 1 oz under each drip emitter each month; mature in-ground trees usually need no fertilizer.
• Potted trees, monthly during spring and summer growth: balanced liquid fertilizer. Feed once a month to support a crop (RHS); stop over winter.

Too much nitrogen gives lots of leafy shoots but fewer olives and poorer oil (UF/IFAS). Overwatering invites root rot.

Harvest

Fruit ripens in late fall, turning from green to black-purple (some stay green or turn copper-brown), and olives often bear heavily only every other year (UF/IFAS; UC Marin). Raw olives are bitter and must be cured before eating.

Olives ripen once a year in late fall, turning from green to black, and trees tend to crop heavily only in alternate years. The fruit must be cured before eating.

Varieties (18)

Pests to watch for

Scale insects, Thrips, Grasshoppers

Diseases and problems

Olive knot, Verticillium wilt, Peacock spot, Root rot, Anthracnose

In the kitchen

Cured olives for the table and pressed olive oil (UF/IFAS; UC Marin).

Keeping it: Fresh olives are too bitter to eat and must be cured first; start curing soon after picking. How long cured olives keep, and whether they need the fridge, depends on the curing method.

Safety: Olive pollen is a common allergen; UF/IFAS notes some cities ban fruiting olives for that reason and sell pollen-free types like 'Swan Hill'. MSKCC says olive leaf extract may add to the effect of blood pressure and diabetes medicines.

Pets: Not listed as toxic by the ASPCA