Olive Nutrition - Q&A

DJ's agronomist Sam Freeman looks at why olive trees turn yellow in winter.

Olive foliage is naturally green, persisting for about two years on the branches in all seasons. There are two main reasons that an olive tree may have yellow leaves at this time of the season.

Olive grove on light, sandy soil - 5/8/2012.
Yellow foliage on an olive tree - 5/8/2012.
If there are just a few yellow leaves scattered throughout the canopy, it may be natural senescence. Since olive trees are not deciduous, they have continual leaf loss through the season. Most olive leaves have a lifespan of two to three years, at which point they will yellow and fall off naturally.

If the majority of the canopy is yellow, it may be a nutrient deficiency that is causing the yellow leaves. Olives do not need a particularly nutrient rich soil, but yellow leaves is an indicator of low plant nutrient levels. A little additional fertiliser once a year early in late winter or spring does improve plant nutrient status, leaf colour and boost the production of your olive trees.

If the yellowing is not caused by nutritional problems then consider if waterlogged soil is the problem. 
Olive with natural grey/green leaf colour.
Overly wet soils may cause olive trees to become stressed and have yellow leaves when they are unhealthy. Poorly draining soils also leads to fungal diseases. When a fungus initially infests a tree, leaves prematurely yellow, die and drop off, making the once healthy olive tree look nude or sickly.