Foliar Fertiliser for Olive Yield: Which Element, and When?

Why the olive tree needs its own nutrition programme

Foliar fertiliser applications that raise olive yield have become indispensable for unlocking the potential of a tree whose cultivation goes back centuries. Olive is known as a drought-tolerant, low-maintenance tree, yet high yield still requires the right elements at the right time. Soil application alone is not enough; foliar fertiliser provides fast, direct nutrient uptake.

The critical elements for olive yield

Boron: flower retention and fruit set

Boron is the most important trace element in olive. Boron deficiency leads to flower drop, poor fruit set and empty fruit. A boron application before flowering in spring can raise the fruit set rate by 20–40%.

Potassium: oil content and fruit quality

Potassium directly determines the quality and quantity of olive oil. Without enough potassium, oil synthesis slows and the oil content of the fruit falls. It also increases winter hardiness and tolerance to water stress.

Zinc: shoot development and leaf health

Zinc deficiency is very common in olive groves and shows itself as "rosette leaf" · internodes shorten, leaves get smaller and cluster together. This severely restricts yield.

Magnesium: chlorophyll and photosynthesis

Yellowing on older leaves is the classic symptom of magnesium deficiency. When magnesium is insufficient, photosynthetic capacity falls and the tree cannot produce enough nutrition of its own.

A stage-by-stage foliar programme for olive

February – March: end of dormancy and shoot growth

As the tree comes out of winter, a zinc + magnesium foliar fertiliser is applied. Early nutrition in this period gives new shoots a strong start.

April – May: pre-flowering and flowering

The most critical period of the season. A boron application should be made 7–10 days before flowering and may be repeated during flowering. It directly affects fruit set.

June – July: fruit development

A potassium + zinc combination is applied in this period, laying the foundation for fruit growth and oil synthesis.

August – September: preparing for oil accumulation

The last potassium application before harvest supports oil content. Nitrogen should be avoided · excess nitrogen lowers oil quality.

November – December: recovery after harvest

A potassium + zinc application renews the tree's reserves after harvest stress. This application is critical for next year's yield.

Alternate bearing and how to manage it

By its nature olive gives a heavy crop one year and a light crop the next. A correct nutrition programme, however, reduces that swing substantially. A potassium + boron combination after harvest supports bud differentiation for the following year and softens the effect of alternate bearing.

Frequently asked questions

When should boron be applied on olive?

Seven to ten days before flowering. Applying boron after the flowers have opened does not contribute to pollination; timing is decisive.

How many foliar applications per year in an olive grove?

A minimum of 3–4 periods is recommended (shoot growth, flowering, fruit development, post-harvest). In total, 6–8 applications can be made.

Is foliar fertiliser useful on well-established olive trees?

Yes. Soil application is also needed on established trees, but foliar fertiliser acts in critical periods · especially flowering · at a speed soil application cannot match.

Is it possible to prevent alternate bearing completely?

Complete prevention is difficult, but a post-harvest fertiliser programme and regular irrigation noticeably reduce its severity.