Potassium (K) is one of the three essential nutrients for plants. It plays a critical role in a wide range of processes, including cell growth, photosynthesis and regulation of water balance. Plants take up K from the soil and circulate it throughout their bodies via molecules called K+ channels. The function of one such K+ channel (called AKT5) in the model plant Arabidopsis thaliana has remained a mystery, despite more than 30 years of study.