The olive tree, Olea europaea, has been cultivated for thousands of years for its fruit and derived oil. This long-lived tree requires a predictable annual cycle to yield a harvest. Understanding the timing and environmental conditions that influence fruit development is necessary for successful cultivation. The journey from bud to harvestable olive is governed by the tree’s age, seasonal progression, and temperature triggers.
Age of First Fruiting
The initial production of olives depends on the maturity of the tree, which is determined by its propagation method. Trees grown directly from a seed have a prolonged juvenile phase and may take between 8 and 12 years to produce their first flowers and fruit. Some seedlings may never bear fruit at all, making this a less reliable method for fruit production.
The time until first harvest is reduced when the tree is grown from a cutting, graft, or purchased as nursery stock. These methods retain the physiological maturity of the mother plant, allowing the tree to begin bearing fruit much earlier. Most grafted trees can be expected to produce their first small crop within three to five years after planting. Early fruiting varieties, such as Arbequina, can begin to produce fruit in as little as two to three years.
The Annual Fruiting Cycle
Once the tree has reached maturity, the cycle of fruit production begins, beginning with new growth in late winter or early spring. The most noticeable stage is flowering, which typically occurs from mid-spring into early summer, usually around May and June. During this period, the trees are covered in tiny white flowers, but only a small percentage of these will be fertilized and develop into an olive.
The fruit set phase follows flowering, beginning in early summer as the fertilized flowers drop their petals and small fruits start to form. Throughout the summer, olives grow in size, and the pit inside the fruit hardens, marking a significant step in their development. This period is when the fruit accumulates reserves, and lipogenesis, the process of turning the olive’s pulp into oil, begins.
The harvest period spans from late summer through winter, with the timing depending on the desired use of the fruit. Olives picked when they are still firm and green are harvested in late summer or early autumn for table consumption. Color change (veraison) begins around September, as the fruit transitions from green to hues of red, purple, and eventually black. Olives destined for oil production are usually left on the tree until late autumn or early winter (October through January) to maximize oil accumulation and flavor intensity.
Essential Climate Triggers
The annual fruiting cycle is governed by temperature, requiring a period of winter cold known as chilling hours. Olive trees are one of the few evergreen species that require this cold influence to induce flower development. Without sufficient chilling, the tree will only produce vegetative buds, resulting in no flowers or fruit in the spring.
Chilling hours are accumulated when the tree is dormant, with temperatures in the range of 40°F to 50°F being most effective. The cold exposure is necessary to release floral buds from dormancy and allow them to differentiate into flower clusters. While the requirement varies by variety and location, many olive varieties need approximately 200 hours of cold to reliably bear fruit. Following winter dormancy, the olive tree also requires adequate warmth during the summer months for the developing fruit to grow, ripen, and accumulate oil.