[April 6] UPDATE: Flower petals are falling on the Quad as the trees lose their blossoms. The waning bloom is still quite a site but it’ll be a while before the trees are back on full display.

[March 23] UPDATE: The cherry trees are officially in peak bloom! Visit campus anytime in the next week or so to see the blossoms in all their glory.

[March 18] UPDATE: Recent temperature swings have slowed bud development for the Quad cherries. About half of the trees are still in peduncle elongation stage while half have moved on to the “puffy white” stage that precedes full bloom. Cool temperatures in the coming days may delay peak bloom as trees gradually blossom. Warm weather could produce a sudden transition. Check the live cams for updates.

[March 13] UPDATE: It’s snowing but the blossoms are still growing! The Quad cherries are now in the “peduncle elongation” stage, where the flower-bearing stalk extends from the bud. Some have also begun to flower.

Each spring, large crowds gather on the ����Ӱ�Ӵ�ý Quad to admire 29 puffy pink cherry trees making their seasonal debut. The trees begin to wake up as the weather warms, and this year, estimates suggest that they will reach “peak bloom” on March 20.

The UW’s iconic cherry trees achieve peak bloom when 70% of the blossoms have opened, but the week before and after still offer visitors an optimal viewing experience.

The cherry blossom visitors’ website provides updates on bloom status as well as details on transportation, activities and amenities. The cherry blossoms also have live video feeds for virtual viewing and their own social media accounts on and .

The cherry trees are both beautiful and ecologically significant. Tracking when the buds burst each year helps researchers predict peak bloom and determine how climate warming is impacting the trees, which were planted in the Washington Park Arboretum in 1936 and then relocated to UW in 1962.

This year, many plants began to emerge early as a mild winter gave way to spring. Recent UW research described how plants rely on both temperature and light cues to time their flowering. Temperature is particularly important to cherry trees, which estimate the arrival of spring based on how cold it has been. They accrue “chilling units” as winter progresses and “heating units” as it yields to spring.

“The buds need to accumulate a specific amount of chilling units before they can start accumulating the heating units. When it is not as cold, the chilling units accumulate much slower, so it takes them longer to wake up from dormancy, which is very counterintuitive,” said , a UW doctoral student of environmental and forest sciences.

Theil is now overseeing data collection on campus, with the help of approximately 20 undergraduate students. The researchers make observations as the trees begin to wake up and feed the data into a computer model that incorporates weather forecasts to predict peak bloom.

Historically, the onset of peak bloom has fallen between March 12 and April 3, with an average date of March 23. While the weather impacts peak bloom year to year, climate change drives longer term trends over multiple decades.

Research shows that bloom time has shifted approximately two days earlier each decade since the 1960s. Researchers began monitoring the trees in 2012 and referenced newspaper archives to estimate peak bloom dates for the preceding years.

“With the climate warming more rapidly in the spring, I expected to see the flowers blooming earlier,” said lead author , a recent doctoral graduate from the UW school of environmental and forest sciences. “But as we dove into the literature and examined the data, we saw a delay in bloom, as a result of winter warming in Seattle.”

The study focused on the Somei-yoshino, or Yoshino, cherry tree cultivar. These trees, sometimes called the Japanese flowering cherry, are found throughout Japan. They also line the National Mall in Washington D.C. and paint many Seattle neighborhoods pink in the springtime.

The bloom delay Maust observed applies only to Yoshino cherry trees in Seattle. In colder climates, such as Washington D.C., the trees have ample time to accrue chilling units. Still, the two populations are quite similar, genetically.

Propagation, or breeding more trees, occurs by grafting one tree onto another. This process limits genetic variability in favor of consistency. Because all Yoshino cherry trees are sterile clones of one another, they do not produce fruits or seeds, but they do reliably bloom in beautiful pink hues each spring.

For more information on bloom time, contact Theil at mtheil@uw.edu or Maust at�� amaust@uw.edu. For information about the Yoshino Genome Project, contact Steinbrenner at astein10@uw.edu.

Bee experts wouldn’t have previously expected to find the likes of Osmia cyaneonitens, Dufourea dilatipes and Stelis heronae in Washington. But this year, researchers added eight new bee species to a list of the state’s native pollinators.��

While collecting pollinators in Chelan County to study how climate and wildfires affect native bee populations, , a ����Ӱ�Ӵ�ý research scientist of biology, discovered never recorded in Washington and 100 species that had not previously been documented in Chelan County. Expert taxonomists from Utah to British Columbia helped her identify the bees, which were photographed in high resolution for her research.��

 ����’s a really exciting moment. Sitting with an expert taxonomist to determine the identity of an undocumented bee filled me with awe,” said Maust, who completed this research as a UW doctoral student of of environmental and forest sciences. “They cited subtle characteristics that I would not have even known to examine. The findings also have important implications for biodiversity. It’s difficult to conserve a species when we don’t know its name or native range.”

Taxonomists refer to detailed sets of characteristics to differentiate bees by family, genera and species. The morphological qualities of bees are incredibly diverse, and individual species can vary in small but significant ways.  Bees can be distinguished from each other by the shape and structure of wing veins, hair color on the ‘terga’ — plates forming the bee’s abdomen — and the location of ‘scopa,’ or pollen carrying hairs.

If you are interested in bees, Maust said, the trains volunteers to find, collect and identify native bees. Individuals can also share bee photos and observations on sites like where the data is made available to researchers.��

Depicted below are a few of the new-to-Washington bees Maust observed and the characteristics scientists focused on for classification. Click the image to see the full resolution photo.

The scopa on the abdomen of this female bee and its heavily pitted ‘terga’ with inflated edges helped Maust to identify it as Dianthidium singulare.

This fierce-looking female Osmia cyaneonitens has huge mandibles (teeth) and flashy blue coloring. Osmia, in the mason bee family, use their large mandibles to move mud or cut leaves or petals to build nests. Their bodies are often metallic blue and green.

This Dufourea dilatipes Maust collected belongs to a rare group of the Halictidae family, commonly called ‘sweat bees’ because they are attracted to the salt and moisture in the sweat of mammals. All members of this family have a strongly arched basal vein on the forewing. Dufourea dilatipes exclusively forages on Calochortus flowers for pollen and nectar. 

Black and brown coloration on the head, abdomen and thorax is one trait of Melissodes nigracauda. This one was caught in a soap/water trap, which Maust said can result in a spiky hairdo sometimes smoothed by “relaxing” the bee and giving it  a blow dry before pinning.��

Stelis heronae, at 4 to 5 millimeters long, is so small it was hard for Maust to pin. It wasn’t described by any taxonomists until 2024, which made it tricky to identify. Stelis heronae is distinguished from other species by the maculations, or colored markings, on its terga. It is a cuckoo, or parasitic, bee that lays its eggs in the nests of other bees. Maust pointed out that female Stelis lack scopal hairs under their abdomens because, like other parasitic bees, they do not gather pollen but instead rely on the pollen stores of their hosts.

For more information, contact Maust at amaust@uw.edu.��

[April 4] UPDATE:�� Our iconic cherry trees are in bloom. Plan your visit to campus using this map, which highlights the locations of different cherry trees on the ����Ӱ�Ӵ�ý campus, including the Yoshino blossoms in the Quad.

[March 31] UPDATE: The majority of the blossoms are in peak bloom, a developmental phase which usually lasts about 10 days.�� This phase can last longer if the weather is cool, calm and dry.

[March 25] UPDATE:�� There are three developmental phases currently visible on the UW cherry trees. The majority of the blossoms are in the “peduncle elongation” phase where the stem is formed and the petals have begun to develop. Many blossoms are in the “puffy white” phase, when the fully formed flowers that are ready to open do so with increased sunshine, warmth and clear skies. Approximately 20% of the flowers in The Quad are in bloom.

[March 24] UPDATE:�� This week’s warm weather in Western Washington will help the UW’s famous cherry tree blossoms open. The trees have entered what scientists call the “puffy white” stage, the final phase before blooming.��

[March 18] UPDATE: The cherry blossoms in The Quad are now in the “peduncle elongation” stage, which is when the stalks supporting the flower protrude from the bud.

The ����Ӱ�Ӵ�ý invites the community to enjoy the iconic Quad cherry blossoms on campus this spring. The 29 cherry trees in the ����Ӱ�Ӵ�ý Quad usually draw large crowds on campus and reach peak bloom the third week of March, and this year is on track to meet that timing.��

Warmer temperatures and mild weather affect when the cherry trees start to blossom and when they reach peak bloom.�� The UW’s Bloom Watch is updated regularly to reflect the current blossom phases, including when peak bloom is expected.

The UW’s iconic Yoshino cherry trees typically bloom March through April, but forecasting the precise dates for prospective visitors is an annual challenge. To refine the prediction, a UW research group is using historical weather data going back to 1966 and student-collected observational data to come up with the timing of peak bloom — and looking at how a warming climate impacts that date. Once the trees reach peak bloom — when at least 70% of the blossoms have emerged — cooler temperatures, dry weather and low wind will keep the blossoms on the trees longer.��

“We found that in Seattle, because our winters are so mild and warm, there’s actually been a delay in the bloom time over the past six decades,” said Autumn Maust, a UW doctoral student in the School of Environmental and Forest Sciences. “The bloom time is shifting a little bit later.”

This is because cherry trees need to accumulate both chilling and warming units — accrued over springtime periods of cool and warm temperatures — to reach a threshold that forces them through the bloom stages. Mild winters, Maust says, mean it takes longer to reach the required chilling units.��

There are dozens of varieties of blossoming cherry and plum trees across the Seattle area, with blooms for some species visible from early February until May. Bloom colors range from white to light rose to dark pink, and cherry trees — unlike plums — have distinct horizontal-line patterns on their bark called . These help the trees “exhale” or release carbon dioxide and water.

But you need not wait for peak bloom to visit campus, the season is underway. The UW maintains a visitors’ website dedicated to updates on the status of the blooms as well as details on transportation, activities and amenities. The Quad cherry blossoms also have their own social media accounts on and . Cherry tree enthusiasts who can’t make the trip can keep up with UW Video’s live webcam overlooking the Quad, a��virtual tour��with photos from campus and tweets from .��

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For more information or to schedule an interview, please contact Dana Robinson Slote: drslote@uw.edu or 206.457.6058

[March 26 update: Peak bloom is set to continue at least through the weekend of March 30-31, according to UW arborist Sara Shores. “The cool weather is helping now,” said Shores. “I believe the blooms will be hanging on into the weekend. The leaves are close and once the leaves begin [to emerge], the blooms are harder to see.”]

[March 20 update: As peak bloom continues, this post was updated to include a video about an ongoing study of the UW cherry trees and the headline was changed from “UW cherry blossoms set for peak bloom in late March” to “Video: Predicting cherry tree bloom timing at the UW”]

[March 19 update: Cherry trees in the UW Quad are at approximately 70% bloom and have entered “peak bloom” stage. “If the weather stays cool, with little wind or rain, the bloom should last about two weeks,” said Autumn Maust, a UW doctoral student in environmental and forest sciences.]

[March 18 update: Thanks to unseasonably warm weather over the weekend, approximately 50-60% of buds on the UW Quad cherry trees are now in bloom, with peak bloom expected to begin by March 19 at the latest.]

[March 15 update:��All trees in the Quad now have pink buds with some florets visible. Approximately 2% of buds on the UW Quad cherry trees are now in bloom.]

[March 13 update: All cherry trees in the Quad are now at the “peduncle elongation” stage of bud development, during which the stalks supporting the florets grow longer. It is one of the last stages before the florets open.]

Cherry trees on the ����Ӱ�Ӵ�ý’s Seattle campus are waking up and getting ready to say hello. For the 29 iconic Yoshino cherry trees in the UW Quad, peak bloom will likely begin after March 20, according to UW arborist Sara Shores.

“Historically, peak bloom in the Quad typically begins during the third full week of March and goes into the fourth week of March. That seems to be what this year is going to look like,” said Shores. “Right now, I would guess that the last two weekends of March are ideal viewing conditions.”

This post will be updated with the latest estimates, which could change based on weather conditions.

Cherry tree fans don’t have to wait for peak bloom to visit campus. The entire cherry blossom season is a great time to visit and see the trees in bloom.�� The UW maintains a visitors’ website dedicated to the school’s cherry blossoms, providing tips for getting to campus and maximizing the tree-viewing experience. The site has updates on the status of the blooms as well as details on transportation, activities and amenities. The Quad cherry blossoms also have their own social media accounts on and , formerly Twitter. For cherry tree enthusiasts who can’t make the trip, campus webcams are a good option for virtual viewing.

The timing for peak bloom — meaning 70% of buds have emerged — varies each year based on weather conditions that the developing buds are exposed to in January, February and March.

“In order to reach peak bloom, buds need to accumulate a certain number of both cold and warm days, known as ‘growing degree days,’” said Marlee Theil, a UW graduate student in the School of Environmental and Forest Sciences.

As of March 8, just over half of the cherry trees in the Quad were at the “peduncle elongation” stage of bud development, during which the stalks supporting the florets grow longer. It is one of the last stages before the florets open and the bloom season begins. The remaining cherry trees in the Quad are also progressing normally, albeit one or two days behind.

Since 2018, a UW research group has been��monitoring campus blossoms��from January to April with the goal of creating a model that will use weather data to predict the timing of peak bloom. Theil currently leads the monitoring team of more than 20 undergraduates.

“The data that we gather will not just help us know in future years when to come to campus to enjoy the trees,” said Theil. “This will also be a valuable research tool to understand how these trees respond to changing environmental conditions.”

There are more than 100 cherry trees on campus. The main species is Yoshino, including the trees in the Quad. Other varieties include the Higan, Hisakura, Kwanzan, Mt. Fuji and Shirofugen trees that can be viewed at��locations across campus. The Yoshino trees bloom earlier than many of the other species.

“Even as bloom season wanes for the Yoshino trees in early April, other trees on campus will be starting,” said Shores.

How long blossoms will remain on the trees this year depends on the weather. Cooler temperatures, less rain and lighter winds all will help keep blossoms on the trees.

For those who wish to avoid crowds on the Quad, visiting on weekdays and in the early mornings are better options. The UW asks that visitors not climb the trees, move their branches or shake their branches, as this can cause damage.

Visitors are encouraged to share their photos by using the����hashtag.

For media inquiries about the cherry trees, contact James Urton at jurton@uw.edu or 206-543-2580. For broadcast media, and from past years are available.