In Search of Chill: Cool Nights Needed for Olive Trees in Greece

After warm spells decimated their harvests, producers in Greece are hoping for cool temperatures during critical growing stages this time around.

Corfu, Greece
By Costas Vasilopoulos
Jan. 29, 2024 14:08 UTC
395
Corfu, Greece

Winter has finally arrived in Greece, with tem­per­a­tures drop­ping from 20 ºC to around 14 ºC in the south of the coun­try and remain­ing below 10 ºC in the north, sug­gest­ing that the country’s olive trees could receive the much-needed chill hours nec­es­sary for rich fruition ahead of the 2024/25 crop year.

In the cur­rent 2023/24 crop year, the com­bi­na­tion of pro­longed warm weather and an off-year’ in the nat­ural alter­nate-bear­ing cycle of the olive trees has led to lim­ited yields of olive oil and table olives across the coun­try.

Olive trees in Greece need around 200 chill hours. Given that we had warm weather in the coun­try until Christmas, the trees need about 20 to 30 days of con­tin­u­ous mild cold weather… to be pro­duc­tive in the next crop year.- Nikos Bartsokas, agron­o­mist

Despite the advent of colder days, pro­duc­ers still have wide­spread con­cern about the impact of the rapid weather fluc­tu­a­tions the coun­try is expe­ri­enc­ing on the next crop.

We are still in limbo when it comes to the fruit­ing of our olive trees for the next har­vest, hop­ing that they will not start to blos­som too early as was the case last year,” Zaharoula Vassilaki who grows 5,000 olive trees on the north­ern Halkidiki penin­sula, told Olive Oil Times.

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According to our con­sul­tant on organic farm­ing, the weather in Halkidiki will likely be very erratic dur­ing the next two months,” she added. Part of February is expected to be cold, while it may get warmer towards the end of the month, and the cold with some snow may return in March. This is a com­pletely irreg­u­lar weather pat­tern we are fac­ing here.”

Vassilaki also said that the olive vari­eties grown in north­ern Greece require more chill hours than vari­eties grown in the rest of the coun­try.

She also noted that the unsta­ble weather that has dom­i­nated Halkidiki in recent years has dis­rupted the pat­tern of olive cul­ti­va­tion on the penin­sula.

The olive trees need a long period of cold weather to hiber­nate and then bear fruit,” she said. When cold and warm weather alter­nate in a mat­ter of a few days, this is sim­ply impos­si­ble. Our fathers and grand­fa­thers were sat­is­fied with one month of con­tin­u­ous cold, but we should be happy with just two weeks of cold now.”

Other olive oil-pro­duc­ing regions across Greece also feel the effects of the abnor­mal win­ter weather.

Messenia in the south­ern Peloponnese, one of the country’s most boun­ti­ful olive oil-pro­duc­ing regions, is expected to yield around 40,000 tons this year, down by more than 30 per­cent com­pared to last year and even lower in some parts of the region.

We grow Koroneiki trees in our area, and we expect to get around half of the pre­vi­ous har­vest,” said pro­ducer Asimakis Demeroukas from Gargaliani, in west­ern Messenia.

The cause is the com­bi­na­tion of high win­ter tem­per­a­tures and the pro­longed drought, which pre­vented the olive flow­ers from turn­ing into fruits,” he added. February gen­er­ally needs to be cold and wet for the olive trees to be pro­duc­tive. However, last February was warm and dry, result­ing in a reduced flow­er­ing of the trees.”

On the island of Lesbos, another tra­di­tional olive oil-pro­duc­ing region of the coun­try lying in the east­ern Aegean Sea, pro­duc­ers have come to terms with the new norm of low olive oil yields.

We had signs in the pre­vi­ous years of the sit­u­a­tion we are fac­ing now,” said local pro­ducer Aristeidis Sifneos.

We have lost the four sea­sons,” he added. The blos­som­ing period in May is not fol­lowed by a robust flow­er­ing-set­ting pro­ce­dure as it should. Instead, we get pro­longed dry weather from May until mid-September and some­times until later.”

See Also:Researchers Study How Lack of Chill Hours Impacts Olive Development, Oil Quality

Last year, the olive oil pro­duced on Lesbos reached 30 to 40 per­cent of the island’s capac­ity. This year, the island’s olive oil yield is expected to fare even lower at only 20 to 25 per­cent of capac­ity. In good times, olive oil pro­duc­tion on Lesbos exceeds 15,000 tons.

Olive trees are usu­ally asso­ci­ated with sunny regions such as the Mediterranean. However, the trees need to be exposed to a cer­tain period of rel­a­tively low tem­per­a­tures in win­ter, known as chill hours, to break bud dor­mancy and pro­duce olive fruits. Chill hours are counted only when the tree is dor­mant, mean­ing it is not actively flow­er­ing or grow­ing.

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The olive tree is one of the few ever­green trees that need the influ­ence of cold to bloom,” agron­o­mist Nikos Bartsokas told Olive Oil Times. The buds that emerge in the sum­mer need low tem­per­a­tures in the win­ter to dif­fer­en­ti­ate into flow­ers and then fruits.”

Some Greek olive vari­eties, includ­ing the Koroneiki, Megaritiki and Kolovi, can form flow­ers at a max­i­mum tem­per­a­ture of 16 ºC,” Bartsokas added. Other vari­eties, mostly grown in north­ern Greece, such as the Halkidiki and Amfissis, need lower tem­per­a­tures of around 12 ºC.”

On the other hand, pro­longed expo­sure to freez­ing tem­per­a­tures below –7 ºC can seri­ously dam­age the olive trees,” he said.

Bartsokas also noted that olive trees tend to have bien­nial crop­ping, bear­ing fruit on shoots a year old.

In May each year, new veg­e­ta­tion is formed simul­ta­ne­ously with the tree’s flow­er­ing, which can reach a length of a few cen­time­ters up to 30 to 50 cen­time­ters,” he said. In May of the fol­low­ing year, this veg­e­ta­tion will pro­duce flow­ers, which will finally become the olive fruits.”

However, in the last decades, we have con­sis­tently used means such as amino acids and trace ele­ments to make them bear fruit annu­ally,” Bartsokas added.

Concerning the 2024/25 crop year, Bartsokas pointed out that the next cou­ple of months will be cru­cial for the fruit set­ting of olive trees in Greece.

On aver­age, and depend­ing on the olive vari­ety and the area of cul­ti­va­tion, olive trees in Greece need around 200 chill hours to bear fruit in spring,” he said. Given that we had warm weather in the coun­try until Christmas this year, the trees need about 20 to 30 days of con­tin­u­ous mild cold weather in February or March to be pro­duc­tive in the next crop year.”

This is the most burn­ing issue in the Greek olive sec­tor this time of the year, and it remains to be seen whether the weather con­di­tions will favor the olive trees and the farm­ers in our coun­try,” Bartsokas con­cluded.



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