Growing up near Washington, D.C., my family made an annual pilgrimage to see the cherry blossoms that signaled the arrival of spring. The tree crowns near the Lincoln Memorial looked like soft pink clouds. As a child, I imagined that was where cotton candy came from.
Cherry blossoms spark similar wonder across the country. Here in Utah, crowds pack the trail around the state capitol building to celebrate the trees’ brief but spectacular seasonal debut.
But those blossoms are more than beautiful — they’re also an environmental signal that scientists watch closely. The timing of bloom depends on a sort of seasonal clock inside the buds that uses temperature as its key cue.
During the winter, cherry trees accumulate what scientists call “chilling hours.” Specialized proteins respond to cold temperatures, which resets the buds’ biological clocks. Conversely, as spring approaches, the trees accumulate “heat units.” When enough warmth follows enough winter cold, the buds burst open.
Researchers track this timing to understand how climate is changing. Warmer springs have generally pushed bloom dates about two days earlier each decade since the 1960s. But warmer winters complicate the story. If trees don’t receive enough winter chilling, flowering can actually be delayed.
So those clouds of pink blossoms are more than a celebration of spring — and possible sources of cotton candy. They’re also living calendars, quietly recording how our seasons are changing.
