In perennial grasses, the reproductive development consists of a series of phenological events that strongly affect the ecological and agronomic functioning of grasslands. The heading of the spike from reproductive tillers is a major phenological event used for grassland management and ranking of cultivar earliness. Heading results from processes that take place several months earlier such as the floral transition and vegetative growth. The interactions between the vegetative and reproductive development are poorly understood, making it difficult to predict the phenology of perennial grasses for different genotypes and environments. The aim of the present work was to assess how the duration of the floral induction (FT) affects the vegetative and reproductive morphogenesis of Lolium perenne. Three cultivars of perennial ryegrass were exposed to four temperature and photoperiod regimes in order to modify the duration of FT. In treatment T0, plants were continuously exposed to high temperatures (HT) and long days (LD). In T1, T2 and T3, plants were first exposed to low temperatures (LT) and short days (SD) for 9 weeks in order to complete the primary induction. Then, plants in T1 were immediately exposed to HT-LD while plants in T2 and T3 were respectively maintained in HT-SD for 3 and 6 weeks before being transferred to HT-LD. Leaf production and elongation rate as well as heading date were monitored on the main tillers of 312 plants. None of the T0 plants exhibited spikes as expected from the absence of LT during their development. In T1, T2 and T3, the number of spiked plants ranged from 58-81% for the earliest cultivar Bronsyn to none for the latest one Tryskal. For Bronsyn, heading occurred significantly later as the duration of the HT-SD period increased (heading date T3 > T2 > T1). Nevertheless, T2 and T3 plants were the fastest to reach heading when expressed in days after exposure to LD. In the same time, the total number of leaves increased with the duration of the HT-SD period as plants remained longer in a vegetative stage. Taken together, these observations indicate that the rate of floral induction depends on the number of leaves on the tiller. Finally, our results showed a positive and additive effect of LD and FT on the rate of leaf elongation. This study highlights that strong interactions exist between the vegetative and reproductive development in grasses. Improving the prediction of grasslands phenology therefore requires to further characterize the effect of the environmental conditions on these interactions as well as their genetic diversity