Risk of Extreme Early Frosts in Almond

In almond, late frost is the main factor determining the viability of the culture in cold areas, and late flowering remains the key factor in addressing this issue. Climate change is causing an increase in the frequency of extreme weather events. In 2021, the cold period in Spain after the Filomena storm (11–14 January), in which temperatures reached −20 °C in some regions, was a clear expression in this regard. In many almond-growing areas, these low temperatures affected the closed flower buds of most of the cultivars, except for the extra-late and ultra-late cultivars and despite the early stage of development of the buds, leading crop failure. In this work, we show that early extreme frost only affected the extra-early, early and late almond cultivars that had overcome their endodormancy and fulfilled 40%, 31% and 23% of their heat requirements for flowering. Extra-late (with only 2% of their heat requirements covered) and ultra-late (still in endodormancy) cultivars were not damaged. These results show the importance of cultivating extra- and ultra-late almond flowering cultivars to avoid not only the late frost but also the early frost during the very early development of the flower buds.