Warming winters are making cherry blossoms bloom earlier, potentially putting their flowers at risk

When Jeff Reinbold, the National Park Service’s superintendent of the National Mall and Memorial Parks, unveiled on March 1 this year’s prediction for cherry blossom peak bloom, he prefaced the announcement with a note of caution.

“Emerging from the third-warmest winter on record,” he said, “this has been a particularly challenging year to read the trees.” 

NPS predicted that peak bloom, which occurs when 70% of the Yoshino cherry blossoms around the Tidal Basin are open, would fall this year between March 22 and 25. Experts later predicted the trees would reach peak bloom on the earlier side of that window, and that still seems likely.

The blossoms’ overall average peak bloom date over the past century is April 4, though the peak has been trending earlier over the last 60 years as winters have grown warmer, NPS spokesperson Mike Litterst said. Peak bloom data started being kept in 1921, with the earliest peak recorded on March 15, 1990, and the latest on April 18, 1958. 

NPS takes into account a variety of factors to predict peak bloom, including winter temperatures, March weather forecasts and bud development. Typically, the trees go dormant during winter and begin to bud at the end of February or early March. But due to warmer-than-average temperatures this winter, the trees never reached dormancy. 

Green buds, the first of six stages of blooming, appeared on Feb. 23 — the second-earliest date in at least two decades, according to NPS data. Last weekend, the buds entered their puffy white stage, one step away from peak bloom — with cooler temperatures earlier this week slowing their momentum to the final stage.

Early blooms aren’t necessarily bad for the trees, Litterst said. But they do make the flowers vulnerable to swings from warm to cold temperatures that are more likely to occur earlier in the year. 

“If we get to where the petals are starting to emerge and then we get a real deep freeze, that can be a problem,” Litterst said when NPS released its initial projection for peak bloom. 

Cherry blossom petals are sensitive to cold temperatures. When warm winter weather makes the trees flower early, a sudden cold snap can kill the flowers before they reach maturity.

That happened in 2017, when about half the Yoshino blossoms were lost in a mid-March snowstorm following DC’s warmest February on record.

“If we have this more erratic weather that’s coming with climate change, that’s really the thing that’s going to cause problems,” said Christopher Walsh, professor emeritus of plant science at the University of Maryland at College Park. “People say, ‘What temperature does it take to kill a cherry tree?’ It’s really not the temperature, it’s the fluctuating temperatures.”

One concern is that if a tree’s bark doesn’t go dormant during a warm winter, a cold snap could kill the bark because it will be unprepared for the drop in temperature, Walsh said. Alternatively, warm sun can reflect off snow on the ground and burn the bark, killing it with heat.

The cherry blossoms must also contend with rising water levels and frequent flooding in the Tidal Basin, Litterst said. NPS is in the early stages of a “massive,” years-long project to repair and improve the sea walls, landscaping and drainage around the Tidal Basin and West Potomac Park to protect the cherry blossoms and nearby monuments from rising waters.

Climate change caused by human activity has made winter temperatures across the U.S. rise faster than other seasons, according to the U.S. Environmental Protection Agency. Winters have warmed an average of nearly 2.5 degrees in Virginia and 3.5 degrees in Maryland since record-keeping began in 1896, EPA data shows. (The report does not include DC.)

Litterst said the Tidal Basin has warmed an average of 2.2 degrees since the 1940s.

And winters are expected to grow only warmer in the coming years as climate change accelerates, likely pushing cherry blossoms to bloom even earlier, experts including Litterst and Walsh said.

While rising temperatures are having a clear impact on when the cherry blossoms bloom, other effects on the trees from a warming climate may not be known yet, said Elizabeth Wolkovich, a professor of forestry at the University of British Columbia who studies how climate change impacts plant communities and leads an annual contest to predict cherry blossom peak bloom dates in four cities, including DC and Kyoto, Japan.

“We know that for some species that are closely related to cherries, if they don’t get enough winter cold, they produce fewer flowers,” Wolkovich said. “I would argue we don’t have a good enough understanding yet of how it works in cherry blossoms, because we haven’t needed to — for a long time, winters were always cold enough.”