The homeostasis of iron (Fe) in plants is crucial for optimal growth and development while preventing oxidative stress. However, about 30% of arable land suffers from Fe deficiency due to calcareous soil conditions. In Arabidopsis, Fe deficiency leads to retarded growth, chloroplast dysfunction, and delayed flowering. This study investigates the interplay between Fe availability and the circadian clock in growth and development. Under Fe-deficient conditions, Arabidopsis exhibits a longer circadian period, potentially mediated by plastid-to-nucleus retrograde signaling. Mutant analysis reveals that central oscillator genes are essential for the Fe deficiency-induced lengthening of the circadian period. Establishing an EMS mutant database identified mutants with altered Fe-deficient circadian responses, highlighting the role of Fe in circadian regulation. The study sheds light on the mechanism of circadian rhythm lengthening via the chloroplast retrograde signaling pathway, offering insights into plant responses to environmental stimuli.