Seeing the Olive Tree as a Living Being

Beware the mistakes in growing strategies when the olive tree is treated as a machine.
Aug. 10, 2020
Rafael Navarro and Susan Hoover

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The metaphors we use to describe our world strongly influ­ence how we relate to it. The same holds true for how we think of our olive trees.

Especially after the onset of the indus­trial rev­o­lu­tion, the olive tree came to be thought of as an olive-pro­duc­ing machine, whereby the more resources we put into it, the more it would pro­duce.

But this approach leads to a num­ber of prob­lems because the deep genet­ics of the tree always have the last word

The olive tree is not a sta­tic machine, it is a liv­ing entity that has evolved over thou­sands of years in the Mediterranean cli­mate where there are extreme vari­a­tions in day-to-day and year-to-year con­di­tions.


This vari­abil­ity trans­lates into vary­ing water and nutri­ent avail­abil­ity, and the olive tree has devel­oped phys­i­o­log­i­cal means for deal­ing with these chang­ing con­di­tions. There are strong day-by-day responses in the olive tree phys­i­ol­ogy, rem­i­nis­cent of how a brain reacts through feel­ings such as fear, fatigue, or moti­va­tion.

By con­sid­er­ing the tree in the not-so-metaphor­i­cal sense of these sen­sa­tions, bet­ter grow­ing prac­tices become clear and we can improve the health of our tree, the qual­ity of the oil it pro­duces, and pave the way to a more sta­ble yearly pro­duc­tion.

Heavy crops and tree fear

From a mech­a­nis­tic view of the olive tree, a heavy crop is always the goal. However, for an olive tree, a heavy crop means that it will have to expend a huge amount of energy to its fruits: olives are rich in very expen­sive” phys­i­o­log­i­cal sub­stances (oil) and min­eral nutri­ents. So in a harsh cli­mate, a great expense of energy can be dan­ger­ous, even to the point that it can put the sur­vival of the tree itself at risk.

If the olive tree senses low water and nutri­ent avail­abil­ity, as a self-defense strat­egy it will severely impair the num­ber of fruits it sets. Could we call this fear?

An ounce of pre­ven­tion is worth a pound of irri­ga­tion

According to a mech­a­nis­tic con­cept of olive tree pro­duc­tion, olive trees should be irri­gated mainly in sum­mer, after the fruit has been set because it is thought that the olive tree will need more water due to high tem­per­a­tures and dryer soil. This is a mis­take and shows that we have not com­pre­hended the phys­i­o­log­i­cal process of the tree’s repro­duc­tive sys­tem.

After deploy­ing nutri­ents and energy to the fruits set in spring the olive tree needs a period of rest in sum­mer. If the tree is exces­sively irri­gated in sum­mer, this rest period is not reg­is­tered by the tree and it thinks” it has to jump into the pro­duc­tion stage too soon and it hasn’t had time to recu­per­ate an ade­quate level of nutri­ents. Therefore, as it notes a lack of nutri­ents it will be afraid to over­pro­duce and risk the dan­gers of nutri­ent deple­tion. So the return­ing crop is neg­a­tively affected. 

On the con­trary, when we con­sider the tree from a bio­log­i­cal per­spec­tive, and under­stand its phys­i­o­log­i­cal nature, we take into account the cycles and phases of tree, and it becomes clear that there is an opti­mum moment for sup­port­ing the tree with water and nutri­ents.

The key moment in this cycle is in late spring (espe­cially if it has been a dry spring) because this is the moment when the tree has to decide on how many fruits to set. So irri­gat­ing just before the fruits are set is the strat­egy that will most pos­i­tively influ­ence pro­duc­tion. And this key moment is often missed. The fun­da­men­tal pur­pose for this is to keep the tree from feel­ing afraid of the future so that it will set an appro­pri­ate num­ber of fruits which, of course, trans­lates into a good crop. 

Fatigue, prun­ing and fer­til­iz­ing

In the year after a heavy crop (the off year), a tree’s nutri­ent reserve will likely be low because the nutri­ents went into the fruits. The buds take note of the late win­ter nutri­tional sta­tus and if the nutri­ent lev­els are low, the buds will develop into leaves, not fruits, and the return har­vest will be low or even null. Could we call this fatigue?

From a mech­a­nis­tic point of view, where the goal is always to reach the high­est pos­si­ble level of pro­duc­tion, the olive tree should not be heav­ily pruned before an on-year in the mis­taken opin­ion of ensur­ing a good har­vest. Likewise, it is com­mon to over-fer­til­ize before the tree sets the fruit, which will make the tree set more fruits than it can rea­son­ably han­dle. These prac­tices ulti­mately exac­er­bate the fatigue a tree will expe­ri­ence. 


On the other hand, agro­nom­i­cal prac­tices that take into account the tree’s bio­log­i­cal sys­tems see that heavy on-year prun­ing, and min­i­mal late spring and early sum­mer fer­til­iza­tion (when the olive tree is about to set the fruit), accom­pa­nied by high fer­til­iza­tion in late sum­mer and fall (when the olives increase in weight) help the tree make it to the fol­low­ing spring in very good con­di­tion for devel­op­ing a new har­vest.

Sometimes it is bet­ter to decrease the crop capac­ity in the short term to obtain an opti­mal crop over the longer term. In other words, rather than hav­ing a heavy crop fol­lowed by an off crop, it is bet­ter to have a con­sis­tent year-to-year medium crop which ulti­mately pro­duces over­all higher pro­duc­tion.

Olive tree moti­va­tion 

In an off-year (a low-crop year), the olive tree has very low fruit demand for nutri­ents and energy, and so it is able to develop long shoots and build up good lev­els of nutri­ents and hor­mones. These hor­mones induce most of the buds on the tree to develop into flow­ers (rather than leaves) and, sup­ported by the robust nutri­tional reserve, many of these flow­ers will set fruit the next year (the on-year). Might we call this moti­va­tion?

The desire to repro­duce

The olive tree, like any liv­ing being, wants to repro­duce. For an olive tree, repro­duc­tion means pro­duc­ing olives, and olives mean crop. Olive tree man­age­ment must go in the direc­tion of hav­ing a non-stressed (non-fatigued, non-scared) tree instead of over-sup­ply­ing addi­tional resources. A non-stressed, i.e. happy, olive tree can pro­duce quite sta­ble yearly crops. 

By under­stand­ing the deep phys­i­ol­ogy and genet­ics of the tree, grow­ers can adjust their yearly and intra-year man­age­ment strate­gies. This will ulti­mately improve the homo­gene­ity of inter-year crops, decrease costs in fer­til­izer and irri­ga­tion, cre­ate health­ier trees, increase resis­tance to dis­ease and pests, pro­duce higher qual­ity oil, higher lev­els of phe­nols, and ulti­mately increase rev­enue.

Rafael Navarro is an olive grove man­age­ment con­sul­tant for Selección de Olivares de Sierra. Susan Hoover is the man­ager of The Rain In Spain.


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