What's Wrong with My Olive Tree?

Olive trees evolved in rocky Mediterranean hillsides with fast-draining soil and long dry spells between rains. Their roots are not built to sit in wet soil and begin to rot quickly when drainage is poor. Once the roots fail, the tree sheds leaves to reduce its water demand, often rapidly and without much prior yellowing.

Olives are evergreen but they react strongly to abrupt environmental change. Moving the tree from outdoors to indoors in autumn, exposing it to temperatures below 20°F, or placing it near a cold drafty window can trigger sudden leaf drop within days. The tree is not dying. It is shedding leaves as a stress response to the change.

Soggy soil starves olive roots of oxygen and triggers rot. As roots fail, the tree pulls nutrients back from its oldest leaves first. The yellowing tends to be uniform across older leaves near the interior of the canopy, distinct from the patchy pattern of a deficiency.

Olive trees are shallow feeders that absorb iron efficiently in well-drained acidic soil, but lock out of it when the soil pH rises above 7 or when roots are waterlogged. The symptom is yellowing between the veins while the veins themselves stay green, and it shows up on the newest growth first. Container olives fed heavily with alkaline tap water are prone to this.

Olive trees take three to five years from planting to reach fruiting maturity, even in ideal conditions. Most single-variety trees are self-fertile but produce far more fruit with a second olive variety nearby to cross-pollinate. Indoors there is no wind or bee traffic to carry pollen between flowers, so blossoms drop without setting fruit even on a mature tree.

Olive trees require a winter dormancy period of several hundred hours below 45°F to trigger spring flowering. Indoor and container trees kept in warm rooms all year often skip this chill requirement and produce no flowers at all. Without flowers there is no fruit, regardless of tree age or sun exposure.

Olive knot is a bacterial disease caused by Pseudomonas savastanoi. It enters through pruning wounds, frost cracks, or leaf scars and forms rough, dark, knobby swellings on stems and branches. Once inside, the bacteria travel short distances through the branch tissue and can spread to neighboring cuts on the same tool. The knots themselves look alarming but the main damage is that they girdle branches over time, cutting off water flow above the infection.

Olive scale and black scale are the most common pests on olive trees. They attach to branches and the undersides of the narrow silver-green leaves, feeding on sap and excreting sticky honeydew. Black sooty mold grows on the honeydew and coats the leaf surface, reducing the photosynthesis the tree depends on. Olive's dense, small-leaved canopy gives scale insects plenty of sheltered spots to build up undetected.

Peacock spot is a fungal disease that appears as dark circular blotches with a yellowish halo on the upper side of the leaves, often with a sooty or velvety center. It spreads in cool, wet weather when water stays on the foliage. Olives grown in regions with wet winters or overhead-irrigated in cool conditions are most affected. Severe infections cause widespread leaf drop.