In the natural environment, days are generally warmer than the night, resulting in a positive day-night temperature difference (+DIF). Plants have adapted to these conditions and when exposed to antiphase light and temperature cycles (-DIF; cold photoperiod/warm night) most species exhibit reduced elongation growth. To study the physiological mechanism how light and temperature cycles affect plant growth, we used infrared imaging to dissect growth dynamics under +DIF and -DIF in the model plant Arabidopsis thaliana. We found that -DIF altered leaf growth patterns, decreasing the amplitude and delaying the phase of leaf movement. Ethylene application restored leaf growth in -DIF conditions and constitutive ethylene signaling mutants maintain robust leaf movement amplitudes under -DIF, indicating that ethylene signaling becomes limiting under these conditions. In response to -DIF the phase of ethylene emission advanced two hours, but total ethylene emission was not reduced. However, expression analysis on members of the ACC synthase ethylene biosynthesis gene family showed that ACS2 activity is specifically suppressed in the petiole region under -DIF conditions. Indeed, petioles of plants under -DIF had reduced ACC content and application of ACC to the petiole restored leaf growth patterns. Moreover, acs2 mutants displayed reduced leaf movement under +DIF, similar to wild type plants under -DIF. In addition, we demonstrate that the photoreceptor PHYTOCHROME B (PHYB) restricts ethylene biosynthesis and constrains the -DIF induced phase shift in rhythmic growth. Our findings provide a mechanistic insight into how fluctuating temperature cycles regulate plant growth.