Axillary buds on lateral branches of ‘Black Satin’ and ‘Hull Thornless’ thornless blackberries (Rubus sp.) were examined from September to May in 1984–1985 and 1986–1987, and in Spring 1988. Initial inflorescence development in ‘Black Satin’ was evident in October; however, most buds remained vegetative until January. Perianth primordia became distinct around the terminal floral apex in some buds in late February to early March. Buds sampled from lateral branches at the top portion of plants were more advanced than buds from the bottom portion at several sampling dates. Axillary buds of ‘Hull Thornless’, in contrast, remained vegetative in all floricane portions until late March. Subsequent developmental rates were rapid and uniform. Once the terminal flower appeared, the most basal floral apex in the primary (A1) axis was next to develop. Remaining floral apices along the axis developed sequentially in an acropetal direction. Neither uniformity and time of bud initiation nor subsequent rate of development appeared to affect the length of bloom period.