Dalmatian Agronomists Experiment with New Pruning Methods

Pruning in Croatian olive groves is in full swing, and the new trend is trim­ming trees into a poly­conic vase. 

This is espe­cially true in Dalmatia, where – unlike Istria and Tuscany – the advan­tages of this form of cul­ti­va­tion are just being dis­cov­ered.

“The advan­tages are mul­ti­ple: it facil­i­tates prun­ing, pro­tec­tion and har­vest­ing,” said Šime Marcelić, an assis­tant pro­fes­sor at the University of Zadar’s depart­ment of ecol­ogy, agron­omy and aqua­cul­ture. ​“The canopy is airy and sunny. The fruits ripen more evenly.”

The type of prun­ing involves trim­ming excess branches on trees between 80 and 120 cen­time­ters high with three to four pri­mary branches. This cre­ates a smaller fer­til­iza­tion area suit­able for a grove den­sity of six to seven meters.

Traditional olive tree prun­ing results in a free-grow­ing form; the inside of the crown dies and does not sprout its repro­duc­tive ele­ments. Instead, these cru­cial parts of the tree grow on the tips of higher branches.

Over time, an ​“olive rain­for­est” is cre­ated when the high­est branches of the trees start to inter­twine.

In Northern Dalmatia, apart from a few excep­tions, the poly­conic vase is not used, even in newer plan­ta­tions.

However, this is start­ing to change and has been spurred on by a recent demon­stra­tion and work­shop held by the Association of Olive Growers of Zadar County.

Among the experts is the young agron­o­mist Stjepan Dević, 29, from Sukošan near Zadar.

“I am grate­ful to Marcelić,” Dević said. ​“He taught me prun­ing and made me fall in love with olive trees.” 

After com­plet­ing his under­grad­u­ate stud­ies at the University of Zadar, he worked for a few years before return­ing to get his Master’s degree in agrotech­ni­cal sci­ences.

Five years ago, he founded an olive grove with 300 trees on his grand­fa­ther’s prop­erty in Sukošan. He also bought an old olive grove with about 40 Oblica trees, which he grafted onto Oštrica, Puljka and other native vari­eties. ​“It was a mir­a­cle; they repro­duced like crazy,” he said with­out hid­ing his sat­is­fac­tion.

Dević also became a cer­ti­fied taster, started work­ing in hor­ti­cul­ture, and offi­cially reg­is­tered his land­scape man­age­ment busi­ness, Hortus Agro, in 2022.

Along with pro­vid­ing advice, his main job is arrang­ing and main­tain­ing gar­dens around tourist vil­las and facil­i­ties. ​“When the prun­ing of the olive trees is fin­ished, I throw myself into the gar­dens,” he said.

Dević and his prun­ing part­ner, Toni Družijanić, demon­strated the poly­conic vase method for Olive Oil Times at a grove near Zadar, recon­struct­ing the crowns and adapt­ing them to the new cul­ti­va­tion form.

According to Dević, a poly­conic vase cre­ates the best pos­si­ble ratio of wood to leaf mass. He and Družijanić are prun­ing 120 trees in the grove into a poly­conic vase. 

“If the prun­ing of one tree takes more than 15 min­utes, it means that some­thing is being done incor­rectly,” said Družijanić, a stu­dent at the University of Zadar. 

Appropriate equip­ment is also required to work quickly and with qual­ity: good sneak­ers, gloves, a brimmed hat and glasses. ​“A stab in the eye from the spear tip of an olive leaf can be fatal,” Dević said. 

The pair use the most mod­ern tools for prun­ing: man­ual and extended elec­tric shears and a one-handed bat­tery saw. Each one car­ries scis­sors in one hand and the saw in the other. In five min­utes, each one can ade­quately prune one tree.

Dević and Družijanić prune 100 to 150 olive trees daily, turn­ing ​“olive deserts” into poly­conic vases. Before, when they worked only with man­ual scis­sors, they barely cut 15 to 20 a day, fin­ish­ing each one ​“dead tired and worn out,” espe­cially since each tool must be clean and dis­in­fected before and after prun­ing.

According to Dević, prun­ing helps reduce the load on the tree, aer­ates the crown and bal­ances out wood and leaf mass. 

It is best to start prun­ing in the sec­ond half of March when it is pos­si­ble to see which buds are leafy or flow­ery, mean­ing they will bear fruit.

Dević rec­om­mends prun­ing at the right time. Pruning too early ​“wakes the tree up,” mak­ing it vul­ner­a­ble to early spring cold snaps. 

Like other agron­o­mists, Dević reit­er­ates the impor­tance of bal­anc­ing wood and leaf mass. The tree should only be a skele­ton that car­ries the leaf mass. 

The next impor­tant thing is light. Every part of the canopy should be illu­mi­nated fully, allow­ing uni­form ripen­ing. The fruits from top to bot­tom are in the same state of ripeness, instead of the fruit on the lower branches being unripe as the fruit at the top ripens.

Dević said the shape of the poly­conic vase enables faster and sim­pler man­ual har­vest­ing, espe­cially with shak­ers. 

Other advan­tages of poly­conic vase prun­ing cited by the agron­o­mist included reduced water needs for each tree and more effi­cient use of soil nutri­ents.

Furthermore, it is eas­ier to carry out pro­tec­tion and foliar fer­til­iza­tion on trees pruned into con­i­cal vase form. The spray more eas­ily dis­perses through­out the tree, even inside the crown.

Dević and other poly­conic vase prun­ing evan­ge­lists argue the prac­tice should be used more widely through­out Croatia to make the coun­try’s olive grow­ers more effi­cient. 

While the first year after prun­ing usu­ally sees a yield reduced by 15 to 20 per­cent, the increased effi­ciency in the future more than com­pen­sates for the first low har­vest.