Olive trees (Olea europaea) are resilient plants, revered for centuries for their longevity and fruit. Understanding their specific temperature requirements is important for successful cultivation, particularly when growing them outside their native Mediterranean climates. Temperature plays a significant role in their overall health, growth patterns, and fruit production.
Optimal Temperature Conditions
Olive trees thrive in a Mediterranean-type climate characterized by warm, dry summers and mild, cool winters. The ideal temperature range for their active growth is between 59°F and 95°F (15°C to 35°C). Consistent moderate temperatures within this range encourage robust foliage and root growth. Commercial olive cultivation often occurs in regions with an average annual temperature of 60-68°F (15-20°C). Adequate sunlight is also important for optimal growth.
Understanding Cold Tolerance
Olive trees are tolerant of cold temperatures, though their resilience varies by variety and maturity. Mature olive trees can withstand temperatures as low as 5°F to 14°F (-15°C to -10°C) without significant damage. Younger trees are more susceptible, with damage occurring around 23°F (-5°C). Sudden drops in temperature or prolonged freezing conditions increase the risk of damage.
Cold damage can manifest as:
Leaf tip burn
Yellowing or browning of leaves
Branch dieback
Trunk splitting
If temperatures fall below 20°F (-7°C), severe damage can occur. While varieties like Arbequina and Mission olives show greater cold hardiness, factors such as cold spell duration, wind, and soil moisture influence a tree’s ability to cope.
Coping with High Temperatures
While olive trees are well-adapted to warm, dry conditions, extreme and prolonged heat can cause stress. Temperatures above 86°F (30°C) can reduce photosynthesis, impacting fruit formation and oil quality. Above 95°F (35°C), growth and physiological processes significantly reduce, especially during flowering and fruit set. Prolonged exposure to 104-108°F (40-42°C) can lead to severe stress, resulting in wilting, leaf scorch, and reduced fruit set or premature fruit drop.
Heat stress can also increase water requirements, as trees transpire more to cool themselves. Insufficient water can lead to leaf turgor loss and decreased photosynthesis. This impacts olive size and quality.
Temperature’s Role in Fruiting and Dormancy
Specific temperature cycles are necessary for olive trees to flower and fruit. A period of cool temperatures, known as “chill hours,” is required for flower bud differentiation. This involves hours between 35°F and 50°F (1.5°C to 10°C), with some varieties needing around 300 hours below 45°F (7°C). Insufficient chill impairs flower formation, reducing yields.
Following the chilling period, warmer temperatures are needed for flowering, pollination, and fruit set. Optimal temperatures for fruit setting range between 71-77°F (22-25°C). Temperatures above 86-90°F (30-32°C) during flowering can severely reduce fruit set due to pollen dehydration and reduced viability. These temperature phases guide the tree’s natural dormancy and reproductive cycles.
Protecting Olive Trees from Extremes
Protecting olive trees from temperature extremes involves preventative measures and active interventions. For cold protection, mulching around the base with a 2-4 inch layer of organic material insulates roots and maintains consistent soil temperature. Wrapping the trunk with burlap or horticultural fleece shields it from prolonged freezes, and covering the canopy with a frost cloth during extreme cold traps warmth. Potted olive trees should be moved to sheltered locations or have their pots wrapped to protect roots.
To mitigate heat stress, adequate irrigation is important, especially during hot, dry periods. Deep watering helps the tree cope with increased heat. Mulching also helps retain soil moisture and can reduce soil temperatures. For young or highly stressed trees, providing partial shade during the hottest parts of the day can be beneficial. Some growers use kaolin clay sprays, which form a reflective film on leaves, to reduce leaf temperature and minimize sunburn.