Perennial ryegrass (Lolium perenne L.) seed crop is a profitable option for arable farmers in Canterbury. To achieve optimal yields there is a requirement of the crop to produce 2000 + seed heads/m² which is the result of >2000 reproductive tillers/m². The aim of this experiment is to quantify the effects of manipulating the tillering dynamics of a perennial ryegrass seed crop through the change in sowing date, sowing rate and grazing. Four sowing dates at 3 week successive intervals from the 27th of March with 4 target population densities of 200, 600, 1000 and 1400 plants/m² were sown. Times of sowing one through three with the population density of 200 – 1000 plants/m² reached the target of 2000+ fertile reproductive tillers/m² required for maximum seed yield. As sowing rate increased the number of vegetative tillers/m² also increased while the number or reproductive tillers/m² remained constant, therefore decreasing the proportion of reproductive tillers/m² as sowing rate increased. A reduction in the proportion of reproductive tillers was also seen with later sowings, along with individual reproductive tiller weight. A target population of 1400 plants/m² was impractical as increased self- thinning occurred and resulted in many of the plants dying before reproductive development. Sowing a Perennial ryegrass seed crop as late as 28th of May regardless of population density, tillering could not compensate for lost thermal time in regards to the production of reproductive tillers.