{Olea europaea}

Boron Deficiency in Olives

Native to the Mediterranean region, tropical and central Asia, and various parts of Africa, olives require a long, hot growing season to properly ripen the fruit, no late spring frosts to kill the blossoms, and sufficient winter chill to insure fruit set. Olives are also grown commercially in California, Australia, and South Africa.

Olives will grow and produce fruit even on extraordinarily poor, stony soils, yet they respond to fertilizers.

Boron is a crucial trace element for olive trees. Fertilizing olive trees with adequate boron is necessary for:

  • Flower formation
  • Fruit set
  • Quality olive oil
  • Stable olive oil

Boron deficiency makes leaves fall and branches die in the upper parts of the tree. Secondary shoots develop at the base of the dieback, and the number of suckers in the lower part of the trunk increases.

The leaves show a distinct apical browning which can extend up to two-thirds of the leaf while the rest of the leaf remains a normal green color. Subsequently, the leaves may become completely yellow and later turn a leathery brown from the apex. In cases of mild boron deficiency, some fruit may ripen normally but most will drop prematurely or become deformed and corky. As the boron deficiency becomes more severe, the olive tree will become increasingly less productive and may ultimately die.

Boron benefits

Boron can benefit your olive crop by:

  • Increasing crop yield
  • Increasing fruit set
  • Improving quality of the fruits
  • Preventing dieback
  • Improving the root system
  • Better resistance to dry conditions

Your boron fertilizer options

Boron supplementation should be included on gravels, sands, and on all soils containing less than 0.5 ppm of boron.

Small amounts of boron fertilizers, such as a foliar application of 20 to 30 grams per tree, can significantly boost olive yields. The critical limit of leaf boron is:

  • Deficient: <19 ppm B
  • Low: 20-30 ppm B
  • Normal: 30-150 ppm B

Solubor® allows you the most flexibility in applying boron fertilizers to olive trees. It can be dissolved alone in water, in liquid fertilizers and/or pesticides, and then applied to the soil or directly onto the foliage.*

*Foliar sprays should not exceed 0.5 lbs/acre of boron per application.


Soil Application (Suggested rates of application)

  Granubor Fertibor
LBS/ACRE 6.25 - 12.5 6.25 - 12.5
KG/HA 14.0 - 35 14.0 - 35

Foliar Application (Suggested rates of application)

KG/HA 5.6
Value in Use
Current Yield (Per Acre)
Expected Sale Price

U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 650 customers with more than 1,800 delivery locations globally. We supply around 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles. Learn more about Rio Tinto.

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