The flexibility of management is an important but little-known part of the utilization value of the permanent pastures. Apart from the usual sense of ‘length of time elapsed from the start of vegetative growth to the date of heading’, is there a definition to characterize it? What is its link with functional diversity? Two experimental lay-outs, the one with 19 grass species from permanent pastures, the other with 18 grassland communities, mown and grazed, yielded data on the phenological stages and the shapes of the growth curves. The index of functional diversity, based on the dry matter contents of leaf blades (DMC) and on the proportion of dicotyledons, is a good indicator of the flexibility of management. For the grassland communities, the dates of the start of growth, of the peak of bio-mass production, and of the peak of flowering, weighted by the abundance of the species, are correlated with the DMC, as calculated from the abundance of the grasses. The peak of growth is all the less abrupt as the diversity of the grasses, with the presence of dicotyledons, is larger.