Relationships between temperatures and blooming dates of apple trees.

Minimum winter and spring temperatures required for flowering of 8 cultivars were investigated by means of a mathematical model which used temperature data for 1927-1947 and 1971-1980 and date of blossoming (20% open flowers) data for these years. Temperature sums ( degrees C days) of temperatures above a particular base [unspecified] from 22 January to blossoming at two sites in the Netherlands are tabulated. The model was not very successful in predicting blossoming dates from temperature data. The data suggest that temperature requirements change at different stages of flower development. Higher temperatures required in February and March than April and May for bud development (predicted by the model) suggest that there is a process which prevents too early development of buds. The data also suggest that in places with a milder climate, the processes required to lift this blocking system might partially take place the previous autumn. (Abstract retrieved from CAB Abstracts by CABI’s permission)