In these days of snow and ice, our thoughts turn to olive trees. These plants are able to withstand our harsh winter conditions, and can tolerate temperatures as low as -8°, -11° C and, in certain cases, even -13° and -14° C, with very little damage. Because of their high water content, leaves and 1-year old branches are the most sensitive organs, and can be killed by temperatures just a few degrees below freezing point. The hardiness of a tree mostly depends on its acclimation period in autumn, when the temperatures gradually decrease.
Some varieties of olive trees, such as Leccino and Grignano, are more tolerant than others to frost. In general, the hardier varieties tend to prolong their vegetative stage, continuing to grow while it gradually gets colder. However, should the temperatures suddenly drop, the less tolerant varieties would have a greater chance of surviving, because, having acclimated earlier in the season, they would presumably be already dormant. Another factor worth mentioning is that when winters are mild, olive trees can easily lose their acclimation. A partial loss of acclimation has been observed when the temperatures are higher than 16° C for six days running. This often occurs in the southern slopes of the hilly countryside in northern Italy, especially in the sunnier days of January.