The effect of temperature and light on flower development in Pelargonium × domesticum

Factors influencing the number of flowers produced in Pelargonium × domesticum cultivar ‘Lavender Grand Slam’, and their rate of development after the plants had been given a period of low-temperature flower induction, were studied.Under short days progressive abortion reduced flower numbers as the temperature regime during the forcing-period was increased. Under long days this effect was less marked and the high-temperature regime advanced flowering by over a month. When long days and high temperatures were used for forcing, it was necessary to maintain a high light intensity, 335 J/cm²/day giving the best results in terms of earliness of flowering and the number of flowers produced. At lower irradiance there was some risk of flower abortion, particularly in the first inflorescence.