Prunus species bloom before leaves emerge. This is possible because flower bud development and growth are supported by reserves, that accumulated during the previous season. In Prunus this reserve is starch.
In Prunus species flower development requires several months, from the end of the previous summer until the following spring. Development is halted during the winter, when the flower buds enter a dormant stage. Chilling requirements are specific for each cultivar, suggesting tight genetic control of this process.
Today’s photo shows flower buds of sweet cherry (Prunus avium). In each bud there are 3 to four flower primordia.