Ocimumspecies show a high degree of variation in herbage and oil yield, and oil composition depending upon the ontogenetical stage of the plant at the time of harvest. Using various chemotypes ofOcimum basilicumvar.glabratum, O. basilicumvar.purpurescens, O. basilicumvar.thyrsiflorum, O. basilicumvar.minima, O. americanum, O. sanctum, O. viride, O. kilimandscharicumandO. gratissimum, the effect of growth stage on oil yield, herbage yield and oil composition was examined over three consecutive seasons. It was found that although the herbage yield for allOcimumspecies/varieties (chemotypes) around the initiation of seed formation (180 days after planting), the maximum oil yield coincided with the maximum herbage yield for onlyO. basilicumvar.purpurescens, O. virideandO. sanctum.For the other species/varieties (chemotypes) examined, the maximum oil yield was found to be at the 50% seed set stage (210 days) or between the 50% seed set stage and the full seed maturation stage (210–240 days). ForO. basilicumvar.glabratum(camphor-type),O. basilicumvar.purpurescensmethyl cinnamate-type),O. gratissimum(eugenol-type),O. viride(thymol-type) andO. sanctum(eugenol-type), the major component reached its maximum around 180 days after planting. ForO. canum(linalool-type) the linalool content did not change throughout its complete life cycle. The maximum content of die major constituent of all overOcimumspecies/varieties (chemotypes) exceptO. viride(thymol-type) occurred at the 50% seed set stage (210 days). Finally, forO. viride(thymol-chemotype) the phenophase for maximum content of the major constituent was between 180-240 days.