Every year Washington D.C. experiences an influx of tourists looking not only for White House tours, pictures at the Lincoln Memorial and investigating the Smithsonian Museums, but to stroll the Mall and streets absorbing the beauty and bounty of blooming cherry trees. The ornamental cherries filling the capital with beautiful blossoms and perfumes were a gift from Japan, arriving in March of 1912. The over 3,000 trees are huge seasonal attraction but planning trips to view them in bloom can be tricky.
Greg Huse, a Smithsonian arborist explains: “The blooms which people come to see each spring were actually created almost a year earlier. In the late summer and early fall, the tree begins to release a protein called an FT protein, which triggers the tree to start forming new flower buds for the following year. The buds are fully formed by the time the tree goes dormant in the winter.” Apparently the blossoms exist on the trees throughout the year, but they just aren’t as showy or even visible.
Flowers for the next year develop inside protectively scaled, tightly packed buds which act as armor for the delicate blossoms. Scales have evolved to protect flowers from harsh winter cold, snow and ice but if there was a sustained cold snap with temperatures consistently in the -20s or below for an extended period, the trees may experience some dieback. That type of extreme weather is not common in regions where these ornamental cherries are planted.
Persistent warmth is the trigger for the scales to soften allowing flower buds to break. Huse continues: While there isn’t a magic number of days, the trees are triggered by a sustained warming trend. That’s why you cannot really predict when they’ll definitely bloom. Sometimes that warming trend comes in March; sometimes it waits until April. The only danger with the trees blooming early is the chance of an early spring frost, which can kill the blossoms.”
If a frost occurs, killing blossoms, that year’s tree tourists are, unfortunately, out of luck. The cherry trees will, however, produce another set of buds within a couple of months.