Plantlets of the winter‐hardy ‘John Franklin’ rose cultivar, derived from nodal sections of greenhouse‐grown plants, were cultured on a modified MS medium. The kinetics of P uptake for 96 h as a function of medium temperature was studied by using32P. Rooted plantlets absorbed significantly (P < 0.01) greater amounts of P at 22°C compared with non‐rooted ones and uptake was linear with time for both. P uptake was also significantly higher (P < 0.05) for rooted versus non‐rooted plantlets at 33°C but no significant difference was observed at 3°C. The results show that roots, previously thought to be mostly non‐functional in nutrient uptake on a culture medium, played a key role in absorbing P at 22 and 33°C.