Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent six days a week. As spring weather settles over the Northern Hemisphere, those barren branches will soon be bursting with color. Just like humans, plants have a circadian clock which helps them tell time. They rely on seasonal changes to both air temperature and sunlight to know that winter is on its way out and that it’s time to bloom. Plants can also tell when we’re stressed out. Longer days and warmer temperatures are the seasonal cues for plants that bloom in the spring. Plants with leaves are particularly sensitive to sunlight, which steadily increases from March until the summer solstice in late June. For plants like daffodils and tulips where the flower comes out of the ground or on branches like cherry trees, increasing temperatures are their main cue to bloom.  University of Washington chronobiologist Takato Imaizumi shares more about how our planet’s plants sense these seasonal changes. How do plants know when to bloom? Spring flowering explained by UW chronobiologist California’s …