Abstract This study aimed to assess the effects of temperature on growth and photosynthetic performance of hybrid Napier grass (a C4 plant) as compared to giant reed (a C3 plant). The plants were grown under 20/16 °C, 28/24 °C and 36/32 °C day/night temperature, respectively, in walk-in growth cabinets. The optimum temperature for plant growth and photosynthesis of hybrid Napier grass was 28/24 °C. At higher or lower temperature, the plants had lower growth rates, dry mass production, and net CO2 assimilation rates. Moreover, at 20/16 °C anthocyanin was formed in the epidermal cells of stems and young leaves probably as a defence strategy of the plants to prevent photo-inhibition damage. Giant reed performed optimal at 28/24 °C and 36/32 °C, but growth rates, dry mass production and net CO2 assimilation rates decreased at the lower temperatures. At the lowest temperature, giant reed had significantly higher contents of chlorophyll in the leaves and lower light compensation points than at the higher temperature. These cold acclimation responses enhance the photosynthetic performance of giant reed at low temperatures, which is an advantage for growth in cold climates, particularly at low light intensities. The results show that the C4 hybrid Napier grass has a low plasticity in relation to growth temperature and, surprisingly, has reduced growth at high ambient temperatures, whereas the C3 giant reed is more plastic and has a high acclimation potential and grows best at high temperatures.