Six subterranean clover cultivars (representing early and late flowering genotypes from three subspecies) were used to describe and quantify their phenological development. The vegetative (V) and reproductive (R) development phases, in response to different environments created by eight sowing dates were quantified. The period from sowing to emergence was constant in thermal time at 110°Cd and the first trifoliate appeared at ~300°Cd. Crops sown in autumn had the longest period from runner initiation until floral bud initiation (R1), which would allow an extended period of grazing, particularly for later flowering cultivars like ‘Denmark’. To maximise seed set (particularly in year 1) a maximum period between R3 and R11 is required (seed set window). This ranged from 319 ± 42.3°Cd for ‘Leura’ to 661 ± 73.1°Cd for ‘Narrikup’. The complete crop life cycle from sowing (V0) to maturity (R11) ranged from 1269 ± 31°Cd (equivalent of 123 ± 6.3 days) for ‘Antas’ sown in July to 2799 ± 47°Cd (300 ± 3.9 days) for ‘Woogenellup’. When sowing occurred in an increasing photoperiod (June–November) the life cycle of all cultivars was 59% shorter than when sown in a decreasing photoperiod. The numeric scale was able to describe all the variation in the phenological phases and could be used to quantify thermal time requirements for specific phenophases. This would allow subterranean clover management to be optimised (husbandry, grazing and seed harvest) at a local level, and provides the basic parameters for inclusion in annual pasture simulation models. Phenological stages for subterranean clover “Denmark” from field experiments, Lincoln University, New Zealand. Phenological phases are vegetative (V) and reproductive (R).