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The growth and flowering of Pentas lanceolata ´New Look´ in relation to the different day and night temperature regimes were investigated under controlled environmental conditions. Plants were grown under 16 different day/night temperature environments ranging from 16℃ to 28℃ with a 12 hour photoperiod. Final plant height and internode length at anthesis were more influenced by the difference between day and night temperature (DIF) than average daily temperature (ADT), day (DT) or night temperature (NT) itself. There were no significant differences in internode and leaf number among all treatments. On the other hand, leaf unfolding rate and lateral shoot number were strongly influenced by ADT in which they increased as ADT increased from 18 to 26℃, but decreased when ADT was over 26℃. Fresh weight increased by increasing ADT from 16 to 26℃, whereas dry weight did not increase when ADT was beyond 18℃. The rate of flower development was also influenced by ADT, resulting in reduction of days to flower as ADT increased. Photosynthetic rate increased until 24℃ DT, then decreased at 28℃ DT, regardless of NT whereas respiration rate increased profoundly from 20℃ until 28℃. Net photosynthetic production was higher in +DIF than -DIF within 16-24℃, but vice versa at 28 ℃. In practice, the best quality of Pentas lanceolata ´New Look´ with a good appearance, compactness, and early flowering could be obtained by day/night temperature combination within 20-24℃.
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