The achievement of stem form depends on several growth traits, such as primary direction of elongation, amount and position of axillary load (fruits and shoots), stem dimensions, mechanical properties of the wood, dynamics of radial growth and active re-orientation due to tension wood and maturation strains. In order to identify which of these factors has the main impact on the final stem form, a biomechanical study was performed on 3 apricot-tree cultivars with contrasted forms. The dynamics of growth and bending, mechanical properties and active re-orientations were quantified on 40 one-year-old stems of each cultivar during a growth season. The measured dynamics of bending show that the main re-orientations occur during two periods: from flowering to “physiological drops” stems bend due to the weight of fruits and shoots; at harvest, stems bend upward due to the drop of fruits. Biomechanical analysis of these two periods shows that the differences in final stem form between cultivars is mainly due to differences in stem slenderness, axillary load and dynamics of radial growth. Mechanical properties of the wood and active re-orientations do not explain the differences in stem form