Predicting spring bloom is an art and a science

Summary

Short Wave: "Predicting spring bloom is an art and a science"

Podcast: Short Wave (NPR)
Date: March 31, 2026
Hosts: Emily Kwong & Aru Nair
Main Guests: Matthew Morrison (Arborist, NPS), Mike Glitters (Communications, NPS), Elizabeth Wolkovich (Forest & Conservation Sciences, UBC)
Theme: Unpacking the precise—and unpredictable—science behind forecasting Washington D.C.’s famous cherry blossom “peak bloom,” and what these blooms reveal about climate change.

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Episode Overview

This episode blends firsthand curiosity, expert voices, and local flavor as co-hosts Emily Kwong and intern Aru Nair go on a “nature quest” to uncover how scientists and park staff predict the cherry blossoms’ peak bloom every spring in Washington, D.C. Along the way, listeners learn about the surprisingly complex science behind the blossoms, the impacts of climate change, and the limitations—and joys—of trying to forecast nature’s showstoppers.

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Key Discussion Points & Insights

The Significance of D.C.'s Cherry Blossoms

• The cherry trees, a 1912 gift from Japan, transform D.C. into “a soft, pink wonderland” each spring (Emily, [01:13]).

• The National Mall hosts about 3,700 cherry trees and millions of flowers ([01:29]).

  “It’s like a flower garden where the flowers are 30ft tall.” – Matthew Morrison, [01:53]

• Their bloom is both fleeting and iconic—sometimes lasting just 5 days, which makes timing the festival tricky ([01:58]).

What is “Peak Bloom”?

• Defined as when 70% of the common Yoshino cherry trees have blossomed ([02:26]).

  “When 70% of those trees have blossomed, we say it’s peak bloom.” – Mike Glitters, [02:32]

• Predicting the timing is a mix of “art and science.”

  “It’s a wild-ass guess—there’s some science involved in that.” – Matthew Morrison, [02:49]

The Six Stages of Cherry Tree Blossoming ([04:50–07:17])

1. Dormant (Winter): Buds, protected by scales, resemble tiny pine cones.
2. Green Bud: Bud scales peel away, revealing fresh green.

   “The first stage of flower development, we call that green bud.” – Matthew Morrison, [05:25]

3. Florets Visible: Tips of the flower begin to show pink or white.
4. Florets Extended: Florets peek out further, “like a mouse opening its eyes for the first time” ([06:06]).
5. Peduncle Elongation: The stem (“regrettable name”) stretches, flower still closed ([06:37]).

   “If you saw the entire length of its torso, it’s more presented.” – Matthew Morrison, [06:53]

6. Puffy White Stage & Full Bloom: Buds swell, then burst into bloom ([07:04]).

The Science Behind Predicting Bloom

• Weather, especially temperature, controls the timeline—no fixed schedule ([07:31]).
• Key Concept: “Bucket of Spring Warmth”

  “Think of it as a threshold of warmth the trees need to reach in order to bloom.” – Aru Nair, [08:01]

• Trees also require “winter chilling”—a period of cold to prepare them to respond to spring warmth ([08:32]).
• Photoperiod (daylength) is another trigger ([09:34]).
• “It’s not just that it’s warm, it’s that they’re also getting a certain amount of sunlight.” – Elizabeth Wolkovich, [09:43]

Weather Variability & Climate Change

• Washington D.C. weather swings—snowstorms to 80°F—make predictions hard ([09:55]).

• DC’s peak bloom has ranged between March 15 and April 18 ([10:09]).

• Even the pros get it wrong:

  “I gave the date and I hit it on the nose… I’ve never been right again.” – Matthew Morrison, [10:31]

• Centuries-old records in Asia show peak bloom dates shifting weeks earlier—clear signs of climate change.

  “Cherry blossoms are effectively like our longest written record on Earth… They’re by far the best evidence of anthropogenic climate change shifting our springs.” – Elizabeth Wolkovich, [11:13] & [11:34]

• Natural events (“phenology”), from birds migrating to flowers blooming, have consistently shifted 2–4 weeks in recent decades ([12:00]):

  “Those events have consistently shifted between two to four weeks…depending on how much that place has warmed.” – Elizabeth Wolkovich, [12:18]

Citizen Science & New Approaches

• Scientists now run competitions for amateur and professional forecasters to predict peak bloom dates, improving models ([12:42]).
• The cherry bloom serves as a case study for understanding broader ecological shifts:

  “All these [fruit] trees are doing the same thing as cherries… to help us understand this mystery.” – Elizabeth Wolkovich, [12:42]

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Notable Quotes & Memorable Moments

• On unpredictability:

  “It’s a wild-ass guess—there’s some science involved in that.” – Matthew Morrison, [02:49]

• On the blooming process:

  “Protected, but aware.” (Mouse-in-nest analogy) – Emily Kwong & Matthew Morrison, [06:06]

• On climate insight:

  “Cherry blossoms are effectively like our longest written record on Earth.” – Elizabeth Wolkovich, [11:13]

• Community engagement:

  “We started the forecasting competition to try to get people to help us understand this mystery.” – Elizabeth Wolkovich, [12:42]

• Experiencing the peak:

  “Somehow it still feels like magic every time that you get to peak bloom.” – Aru Nair, [13:41]

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Key Timestamps

• [01:26] – D.C. cherry blossom lore and stats
• [02:26] – What is peak bloom? Definition from NPS staff
• [05:02–07:17] – The six stages of cherry tree blossoming
• [07:31] – The challenge of predicting bloom: role of weather and temperature
• [08:26] – The “two bucket” system: winter chilling & spring warmth explained
• [10:09] – Impact of weather swings, unpredictability of bloom, record extremes
• [11:13] – Humanity’s millennium-long cherry blossom records; climate change signal
• [12:42] – Citizen science competitions for predicting bloom dates
• [13:13] – This year’s blooming: “It’s happening right now” and scene at Tidal Basin

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Episode Tone & Style

Friendly, accessible, and infused with wonder for nature and a dash of dry humor. The hosts demystify science through plain talk, helpful metaphors (“bucket of warmth,” “like dough that has to chill”), and enthusiastic field reporting.

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In Summary

This “Short Wave” episode masterfully explores how both scientific rigor and human intuition are used to predict the fleeting cherry blossom peak in Washington, D.C.—a task that is becoming even trickier due to global climate shifts. Through expert insights and community engagement, the show highlights how these beloved blooms are not only a sign of spring but also a sensitive marker of our changing world.

Transcript

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[Emily Kwong]

Hey, short waivers. Emily Kwong here with a quick favor to ask. Can you send us a voice Memo to Short WavePR.org with your questions about science and specifically about your local environment? That would help a lot. Include your name, where your home is and your question, and we might consider it for a future episode. Thank you so much. You're listening to Shortwave from npr. Hey, everyone, Emily Kwong here with someone very special to our team, shortwave intern Aru Nair.

[Aru Nair]

Hey, Emily, what's up?

[Emily Kwong]

You and I are at NPR headquarters in Washington, D.C. and it's your first time living in the District. How's it going?

[Aru Nair]

It is. I'm originally from Wyoming, and I moved to D.C. last fall. My favorite part has definitely been the public transit. It's very magical to me.

[Emily Kwong]

It's a joy to ride.

[Aru Nair]

But there is one particular event that happens every spring that's a huge deal. Emily, have you heard of the Cherry Blossom Festival?

[Emily Kwong]

You can't escape it this time of year. The cherry blossom marketing is everywhere. But originally these blossoms came from trees gifted by Japan in 1912, and now they turn the city into this soft, pink wonderland.

[Aru Nair]

Yeah, there's so many trees in bloom right now. Yeah.

[Matthew Morrison / Mike Glitters (National Park Service staff)]

So we have 20,000 trees park wide. But of the cherry trees in particular, we have right around 3,700.

[Aru Nair]

So this is Matthew Morrison. He's an arborist and urban forester with the National Park Service. And he told me every single year, locals and tourists flood the National Mall for the annual Cherry Blossom Festival to view these millions of flowers.

[Matthew Morrison / Mike Glitters (National Park Service staff)]

It's like a flower garden where the flowers are 30ft tall. It's really what it is.

[Aru Nair]

But as you know, Emily, these flowers are really fragile and they're only around for a couple of weeks. And in some cases it's spinach short as five days. So the festival is ideally planned for when all these trees are in peak bloom.

[Emily Kwong]

It does feel like Pennsylvania has Groundhog Day. And we have this, like, this is DC's homegrown sign of spring.

[Aru Nair]

Right. And I wanted to know what is peak bloom really? So I asked Mike Glitters to define it for me. He's the chief of communications for the National Mall and Memorial Parks.

[Matthew Morrison / Mike Glitters (National Park Service staff)]

We've got a dozen different varieties of trees, but the Yoshinos are far and away the most prevalent. So when 70% of those trees have blossomed, we say it's peak bloom.

[Emily Kwong]

Okay, so when 70% of Yoshino cherry trees are in bloom, that is peak bloom.

[Aru Nair]

Exactly. And the National Parks team, it's actually their job to predict when the peak bloom will arrive every year. And let's just say it's kind of a guesstimate.

[Matthew Morrison / Mike Glitters (National Park Service staff)]

It's a wild ass guess. There is some science involved in that

[Emily Kwong]

today on the show, the art and science of guessing peak bloom.

[Aru Nair]

What are the stages of cherry tree blossoming and how do scientists make that big prediction?

[Emily Kwong]

You're listening to Short Wave, the science podcast from NPR

[Aru Nair]

Foreign.

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[Emily Kwong]

Once again, we are on our monthly nature quest, brought to you by someone who's paying attention to how their local environment is changing. And this month, that person is shortwave intern Aru Nair. So what. What goes into a cherry tree bloom? A ru.

[Aru Nair]

Well, I didn't really know. So to find out, I went with one of our producers, Hannah. Chin down to the tidal basin. It was damp and chilly. You could hear the jets overhead and the trees looked totally bare.

[Emily Kwong]

That sounds like D.C. in winter.

[Aru Nair]

Yeah, we went there to talk to Matthew.

[Matthew Morrison / Mike Glitters (National Park Service staff)]

I've been an arborist since 1979. I oversee everything to do with the trees.

[Aru Nair]

He told us there's six stages of cherry tree blossoming.

[Emily Kwong]

I love a numbered list. Okay, walk me through these stages.

[Aru Nair]

So to set the stage, in winter, the trees are dormant. It's like they're sleeping. And on these dormant trees, the tips of the branches are covered in overlapping bud scales. These modified Leaves that protect the bud to be, if you will. To me, they kind of look like little pine cones. But once spring comes and it starts

[Matthew Morrison / Mike Glitters (National Park Service staff)]

to get warmer, the scales will peel away, and then you'll have the first stage of flower development, and we call that green bud.

[Emily Kwong]

Okay, so stage one, green bud, where a flower bud emerges but it's protected by green leaves. What is stage two?

[Aru Nair]

So stage two is when the florets are visible. And that just means that the bud is starting to open up.

[Matthew Morrison / Mike Glitters (National Park Service staff)]

And when that bud opens up, just like the bud scales did, you can see the little tips of the flower in there, the florets. It's like a little floweret. You can see the pink or the white in there.

[Aru Nair]

And stage three is when the florets extend.

[Matthew Morrison / Mike Glitters (National Park Service staff)]

The florets are just a little bit more exposed. I kind of think of like a mouse in a nest that kind of opened its eyes for the first time and looking around, and it's still protected, but it's aware.

[Emily Kwong]

Yes, protected, but aware. So the florets are peeking out. What then happens in stage four?

[Aru Nair]

You're definitely not going to guess this one. It's called peduncle elongation.

[Emily Kwong]

Yeah, I would never guess that. What is that?

[Aru Nair]

Yeah, I was also a little bit befuddled.

[Matthew Morrison / Mike Glitters (National Park Service staff)]

So the peduncle elongation is when that flower, the petals are still closed, but it's elongated. And you don't just have those little tips. It would be as if that mouse that I just said as an analogy, if you saw, like, the entire length of its torso, it's more presented. And that's the peduncle elongation.

[Emily Kwong]

Regrettable name, but please continue.

[Aru Nair]

Regrettable name for sure. And then there's the fifth stage, which is puffy flower.

[Matthew Morrison / Mike Glitters (National Park Service staff)]

It's not opened like a regular flower, but the petals are entire. They're still kind of protecting one another. And then after that, it opens up and we have full bloom.

[Aru Nair]

And full bloom is the final stage.

[Emily Kwong]

This is so cool. So how do folks at the national park possibly predict this? Like, are they just running around checking all 3,700 cherry trees to see what kind of stage they're at?

[Aru Nair]

I mean, kind of, because it's not like each stage takes a set amount of time. This bloom cycle is super dependent on the weather and specifically the temperature. So I talked to Elizabeth Wolkovich about this. She's an associate professor of forest and Conservation sciences at the University of British Columbia.

[Elizabeth Wolkovich]

You can think about a bucket of spring warmth that the plant needs to fill before it can Produce enough energy to produce the flower.

[Emily Kwong]

Wait, what does she mean by a bucket of spring warmth? Like a physical bucket.

[Aru Nair]

So not a physical bucket. Think of it more like a threshold of warmth that the trees need to reach in order to bloom. So different plants have different sized buckets to fill. Cherry trees have smaller buckets, which is why they come out so early in the spring.

[Emily Kwong]

Oh, okay. Compared to something that blooms later in the spring, which may have a larger bucket of warmth.

[Aru Nair]

Exactly. Yeah. But it is a little bit more complicated than that, even for cherry blossoms.

[Elizabeth Wolkovich]

So for most woody plants, we think there's actually a two bucket system. And cherry trees have this as well.

[Emily Kwong]

Two buckets. What is the second bucket?

[Elizabeth Wolkovich]

It's often called the winter chilling bucket. So it's the idea that the plants need a certain amount of cool weather before they can start to fill that bucket of spring warmth.

[Aru Nair]

The period of cold that the plants need before they get ready to bloom. It's called winter chilling. And scientists have observed this for a while. You might have observed it too.

[Elizabeth Wolkovich]

If you go outside and you take a cherry blossom in in December, it'll take a really long time to bloom. If you go outside right now and you take a cherry blossom in, or if you went three weeks ago or four weeks ago and you brought it inside, it'll bloom right away.

[Emily Kwong]

You know, this kind of reminds me of baking. You know how you have to chill dough in order to bake it? The trees have to chill a little bit before they'll bloom in the heat.

[Aru Nair]

Exactly. They need both parts.

[Emily Kwong]

Yeah.

[Aru Nair]

And just to be clear, Emily, this winter chilling bucket is something that scientists are still studying. They know the plants need the cold weather to bloo on time, but they're still not quite sure exactly how it works. And Elizabeth told me there's also the factor of longer days.

[Elizabeth Wolkovich]

Additionally, a lot of the plants appear to need a certain number of daylight hours for that spring warming. So it's not just that it's warm, it's that they're also getting a certain amount of sunlight.

[Emily Kwong]

Okay, so Elizabeth is saying to bloom, there needs to be a combination of triggers. Trees need the winter cold, they need the spring warmth, and they need longer days in order to begin the blooming process.

[Aru Nair]

Yeah, exactly.

[Emily Kwong]

You know, we have had a really strange winter in D.C. there's been this pendulum swing between multiple snowstorms and then warm 70, 80 degree days. So did any of the folks who work with the trees describe how this weather is affecting the cherry blossoms?

[Aru Nair]

Yeah. So basically, this up and down weather pattern can totally shake up their predictions. And there's a big range of possibilities. DC's Peak Bloom has been recorded as early as March 15 and as late as April 18.

[Emily Kwong]

What is Mike's office's track record of, of accuracy for predicting peak bloom?

[Aru Nair]

Well, sometimes they're really accurate.

[Matthew Morrison / Mike Glitters (National Park Service staff)]

I started in 2019, and so they said, all right, Morrison, what's the date? And I gave the date and I hit it on the nose. And I was like, Mike, I'm like, ah, I'll do this every year. I've never been right again.

[Aru Nair]

Oh, wow. Yeah. Mike even remembers one particularly chaotic year where they announced their prediction, updated the date, and then they had to change the date back again back to their original prediction.

[Emily Kwong]

Because in making the predictions, they're also gathering what the trees are actually doing every year.

[Aru Nair]

Yeah. And Matthew and Mike are not the only ones focused on peak bloom and predicting peak bloom. Elizabeth told me humans have been recording cherry blossoms around the world for hundreds of years.

[Elizabeth Wolkovich]

Cherry blossoms are effectively like our longest written record on Earth. They go back over a thousand years

[Aru Nair]

in Asia, which she says is really useful for scientists like her who want to study how the timing of those natural events shifts.

[Elizabeth Wolkovich]

In the Kyoto record, they have this long term record. There's also a record out of China. Cherry blossoms across the world are blooming weeks earlier than they did in the past. They're by far, I would say the best evidence of anthropogenic climate change shifting our springs.

[Emily Kwong]

Earlier, I didn't realize how much insight cherry blossoms provided in this way. I remember in an earlier Nature Quest episode, we talked about this. This devoted to the timing of periodic natural events. Flowers blooming, birds, migrating animals going into hibernation. It tells us something across the globe.

[Elizabeth Wolkovich]

I would say whether it's grasses starting to germinate, whether it's the leaf out of beech trees, whether it's flowering on a plum tree or a cherry tree. Those events have consistently shifted between two to four weeks, depending on exactly what plant you're looking at and how much that place has warmed.

[Emily Kwong]

Two to four weeks doesn't sound like a lot, but in the life of the environment, that is a big difference.

[Aru Nair]

Yeah. And Elizabeth and her colleagues were like, given all this data, plus the reality of a warming planet, how do we make these predictions more accurate? So they started running a competition asking people to share their predictions for cherry tree peak bloom in places in the us, in Japan, in Switzerland, in Canada

[Elizabeth Wolkovich]

as a gateway to better forecast what forest trees are doing and what every fruit tree, peaches and plums, all these things are doing the same thing as cherries. And so we started the forecasting competition to try to get people to help us understand this mystery.

[Emily Kwong]

That is a good way to get community scientists involved. Make it a competition.

[Aru Nair]

Exactly. And they're hoping that turns into better forecasting models that scientists can use in the future.

[Emily Kwong]

So to bring this back home to D.C. when is peak bloom supposed to happen for us? This spring?

[Aru Nair]

It's happening right now. So I was thinking maybe we could go out and see them.

[Emily Kwong]

We are here together looking at the cherry blossoms right now. They're so pretty, very, very beautiful.

[Aru Nair]

And so many people are out today.

[Emily Kwong]

So many people. And you talk to a lot of them.

[Aru Nair]

It's a symbol of spring. I enjoy the sunshine and the blossom.

[Emily Kwong]

Like, I have never seen it this beautiful. Like, I've never seen it this, like,

[Aru Nair]

crisp and peaky feeling is I am in another country, like in Japan. I don't know. Somehow it still feels like magic every time that you get to peak bloom.

[Emily Kwong]

Aru Nair, thank you so much for bringing us this glorious nature quest.

[Aru Nair]

Oh, thanks so much, Emily.

[Emily Kwong]

This episode was reported and produced by Arundhati Nair and Hannah Chin. It was edited by our showrunner, Rebecca Ramirez. Burly McCoy, Angela Zhang and Tyler Jones checked the facts. Robert Rodriguez was the audio engineer. I'm Emily Kwong. Thanks for listening to Short Wave, the science podcast from N.

[Aru Nair]

We were here maybe three weeks ago and they looked dead. Hannah and I, we were like, are the trees alive? I don't know. But now it's, yeah, it makes a world of difference to see them bloom.

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[Emily Kwong]

these days it feels like the news changes every hour. Well, NPR has a podcast that does that too. NPR News now brings you a fresh five minute episode every hour of the day with the latest, most important headlines in episodes that are clear, fact based and easy to digest. Listen to NPR News now on the NPR app or wherever you get your podcasts.