One of the many cherry trees at the Tidal Basin that could reach peak bloom later this week. (John Sonderman/Flickr)

Over the past couple of weeks, we’ve been talking about how the exceptionally warm February (a record, even!) would lead to cherry tree peak bloom much earlier than normal — potentially a record. What didn’t become obvious until late last week, though, is that this year’s peak bloom may not be so much of a quick, synchronous peak as a long, drawn out affair that could last a couple weeks instead of a few days.

On Wednesday, March 1, the temperature in Washington spiked to 80 degrees and tied the record for the date. When the tree-watchers at the National Park Service went out to check on the blossom status, they found the majority were in “florets visible” stage.

On the same day the photo above was taken, one of our contributors John Sonderman took the photo below, which shows other trees already at the “peduncle elongation” stage.

If history tells us anything, it means these trees are only one week away from full-bloom.

In order of appearance, the stages are:

  1. Green color in buds
  2. Florets visible
  3. Extension of florets
  4. Peduncle elongation
  5. Puffy white
  6. Peak Bloom

The peduncle is a funny word for the part of the stem that holds the flowers. One peduncle can contain up to four or five blossoms. This part of the tree extends just before the florets bloom. In John’s photo below, you can see how the peduncle has extended beyond the brown bud encasing.


A photo of cherry trees in peduncle elongation stage at the Tidal Basin on March 2. (John Sonderman/Flickr)

As of Monday, two of the older trees on the Tidal Basin are in full bloom, according to the National Park Service’s Michael Stachowicz, but the trees are spread out among stages. The majority — 60 percent — are in the “florets extended” stage, but 20 percent of them are already at peduncle elongation.

Last year it only took eight days to transition from peduncle elongation to peak bloom. There have been years in the recent past when the trees zipped from elongation to peak bloom in less time than that, but using one week as a conservative forecast from this point, these trees will be in peak bloom at the end of this week.

So you know I’m not just a cherry-blossom alarmist, Stachowicz is right there with me. In fact, he called this year’s progress “fascinating.”

First, some background math. There is a temperature — approximately 40 degrees — above which the cherry trees believe it to be “warm.” On warm days, they take advantage of the soil moisture and soak up the sun and some carbon dioxide and their little branches and buds grow. When the temperature is lower than 40 degrees, they put out a hold: No new growing until it warms up again.

In essence, the temperature is like a timer. The more “degrees” that accumulate, the closer the trees are to peak bloom.

“At the end of this warm spell [March 10] we will have accumulated 208 of the 221 heating degrees needed for bloom,” Stachowicz told us.

So technically, the blossoms still need 13 “heat degrees” to trigger peak bloom. But that doesn’t mean it will take 13 days to happen — far from it.

“It would only take one freak warm day to bring us back,” Stachowicz explained. “[Thirteen] heat degrees can be added with a 70 degree day and 50 degree night. We are so close as far as accumulated degrees it wouldn’t take much.”

If you’re excited about the prospect of early blossom watching, you may want to head down to the Tidal Basin on Friday or Saturday before things turn cold again. You may see quite a few trees that are at or near peak.