Preliminary Results on Seasonal Changes in Flower Bud Cold Hardiness of Sour Cherry

Irregular yields of Prunus cerasus ‘Stevnsbaer Birgitte’, which is the preferred sour cherry cultivar in Denmark, have been proposed to be a result of freeze injury to floral tissues. This study determined floral mortality of P. cerasus ‘Stevnsbaer Birgitte’ and the supposedly more cold hardy P. cerasus ‘Kelleriis 16’ under natural conditions, and investigated seasonal changes in flower bud cold hardiness of ‘Stevnsbaer Birgitte’. In a cold winter with unusual low temperatures in December, the injury rate of buds of ‘Stevnsbaer Birgitte’ was significantly higher than that of ‘Kelleriis 16’, confirming that buds of the latter cultivar are considerably more cold hardy than buds of ‘Stevnsbaer Birgitte’. The majority of frost injuries in buds of ‘Stevnsbaer Birgitte’ occurred mid-winter, but dehardening appeared fast, indicating that the critical injury times of buds of ‘Stevnsbaer Birgitte’ include both the mid-winter and dehardening phases.