All deciduous fruit trees require a minimum period of winter dormancy so that they can flower and bear fruit successfully when spring arrives. This need for dormancy is known as “chill hours”.
In fruit growing, ‘chill hours’ are measured from the time the plants lose their leaves, that is, when they are dormant, roughly from November to March, depending on latitude, climate zone and other factors.
Although there are various scientific formulas for measuring them, the basic method is to add up all the hours during the aforementioned period when the temperature is below 7°C, including sub-zero temperatures. The distribution of these chill hours throughout this period also plays a role.
In this way, we can determine which species or varieties are suited to our climate zone, as, within the same species, there may be varieties with different requirements for ‘chill hours’.
Prepared and written by Adrián García Villar, Agricultural Engineer from the Polytechnic University of Madrid (UPM). Membership No. 215, Official Association of Agricultural Engineers of the Principality of Asturias (COIASTUR).
References:
Juan Carlos García, Guillermo García González de Lena, Marta Ciordia Ara, (2018).