The Evening Primrose Nature Show

Coming to Yosemite to watch flowers open may sound like the beginning of a joke — Did you hear the one about the guy who went to Yosemite to watch the flowers open?

And yet, watching the evening primroses open in our yard is one of our great pleasures of summer. The nightly show is so stunning that it was once one of the principal attractions of Yosemite, rivaling Half Dome and the giant sequoias with visitors in the early 1900s. And then, just as Yosemite became world-famous for those blooms, they were gone forever. But when the deer are kind to us, we recreate a bit of that magic in our yard.

Read on to learn about evening primroses.

  • Part I: About Evening Primroses
    • Why is watching a flower exciting
    • A bit about their ecology
  • Part II: The Story of the Rise and Fall of Evening Primroses in Yosemite
    • How they came to be a major attraction in Yosemite around 1900
    • How they came to disappear and whether that’s a good thing or a bad thing.

Though normally I think that being a historian is a thing I used to do, old habits die hard. I’ve been reading and speaking about this for years and wanted to finally organize my notes. So Part II really gets down in the weeds (bad pun, I know) on the history of evening primroses in Yosemite. But you can just look at the pictures and videos if that’s more your speed!

What’s so exciting about watching a flower blossom?

In the case of Oenothera elata, aka Hooker’s evening primrose, the yellow blossom almost the size of the palm of your hand opens most of the way in just a few seconds. When people see video of it, they usually think it’s a time-lapse. On the best nights at our house, it happens over 100 times in about 40 minutes (unfortunately, the deer wiped out most of the 2021 crop).

A few years ago, our friend Russ of Yosemite Hikes fame took this one-minute video in our yard. It will give you a sense of how fast the evening primrose opens. This real time, not at all sped up:

Real time video of an evening primrose opening and a sphinx moth arriving

This shorter video is a time-lapse that shows a five blossoms opening in 15 minutes and 17 seconds, compressed into about 12 seconds.

Evening primrose time-lapse. Total real time: 15:17.

At first, we thought this was just a strange thing that we got excited about. Over time we’ve seen young boys and teenage city girls and middle-aged men and others of all ages and interests get excited. And as our knowledge of Yosemite history grew, we learned that it was a major Yosemite attraction over a century ago that advanced the technical aspects of photography and motivated people to pay more attention to preserving the meadows of Yosemite Valley.

The evening primrose is a biennial. The first year it grows with just a basal cluster of leaves — no stalk and no flowers. It’s just putting out leaves and capturing as much solar energy as it can to store in its roots for the big show the next year.

The second year, it uses that stored energy to grow as high as four feet tall and can have a few dozen blossoms. The blossoms last for only one night, coming out at sunset in order to avoid having their precious pollen and nectar taken by day-flyers that are not as effective at pollinating them as the sphinx moth. In the full heat of the summer, the blossoms will be wilted and “dead” by 11am.

The pistil, that long thread with the cross at the end (called the stigma) in the middle of the blossom, is the pollen receiver. If you pull it out the filament is 2-3 inches long. Around it are the stamens with a sort of gooey pollen that sticks to the moth (or bee) and travels with them to the next blossom. The pollen grain brushes off on the cross-shaped stigma, then travels all the way down that tube to the ovaries to fertilize the seeds. The plant then makes hundreds of seeds for every seed pod. The pods eventually dry out and open and that tall plant, blowing back and forth in the wind, ejects the seeds a fair distance, like Father O’Connor spraying the congregation with holy water.

evening primrose blossom closeup
You can see the stamens laden with pollen. That sticky pollen holds onto the moth and the moth carries the pollen grains to the next blossom.
closeup of evening primrose blossom
The same blossom in Sentinel Meadow, from a different angle, showing the pollen on the stamens better.

More on the evening primrose

Is that a bird?

Notice the supporting cast in that video. It looks almost like a hummingbird when you first see it flying, but you will soon see that it’s the gorgeous White-lined Sphinx Moth (Hyles lineata).

hyles lineata dorsal view
Hyles lineata, by Didier Descouens via Wikimedia Commons under the Creative Commons Attribution-Share Alike 4.0 International license.

The sphinx moth’s secret weapon is a very long proboscis that lets it reach deep into flowers that have a large nectar reward. They are known to frequent columbines and we have seen them on pennyroyal, but the evening primrose is clearly a favorite. The sphinx moth is a major evening primrose pollinator, while the evening primrose provides food not just for the adults who come for the nectar, but for the caterpillars as well (though, sadly, we’ve never seen one on our evening primroses).

Hyles lineata with long proboscis feeding on nectar
The impressively long proboscis of the White-lined Sphinx Moth. Photo by Larry Lamsa from Flickr and Wikimedia Commons and used under the Creative Commons Attribution 2.0 Generic license.

Their timing is impressive. We rarely see these moths, but within minutes of the first blossom opening, they arrive. To our human noses, the smell of the evening primroses is subtle. Apparently for a sphinx moth, it’s like Mama Ciccardi’s famous marinara sauce cooking on the stove — within minutes, the smell wafting from the flowers calls them to dinner from the far corners of the neighborhood.

Other pollinators

The sphinx moth is not the only pollinator. We see other insects in the flowers sometimes, but typically only in the morning. Carpenter bees (specifically Xylocopa tabaniformis) can be a major pollinator and the overlap in the range suggests this is an ancient relationship (Barthell and Knops). In our experience, though, it is the sphinx moth who rules the skies over and around the evening primroses when they open.

When does this happen?

In drought years and wet years, hot years and cool years, the first blossoms are always within a couple of days of Theresa’s birthday at the end of June. The show reaches its peak in early July and goes strong through most of the month and fades by early August, after which it’s just a few blossoms here and there. We’ll still get the occasional blossom into October, sometimes on plants that appear all but dead.

Where does this happen?

The evening primrose is not a rare plant, but it is a favorite food for deer. So while widespread, there are typically only a handful in Yosemite Valley that blossom each year. A century ago, that number was in the thousands, perhaps tens of thousands, but those days are gone (that’s the story of Part II). To the best of our knowledge, the best places to see them are just east of Tioga Pass along Highway 120 (a terrific display there in good years) and at our house, except in those years like 2021 when the deer ravage “our” plants (they aren’t “ours” of course any more than we are theirs).

A primrose by any other name

The evening primrose, by the way, is not closely related to the primrose, just like the primrose is not closely related to the rose. They are three distinct flower families belonging to three separate orders. In fact, the evening primrose is more closely related to the rose than to the primrose. To get technical, roses (Rosaceae family) and evening primroses (Onagraceae family) both belong to the Rosids clade, while primroses (Primula family) belong to the Asterids clade.

Part II: The rise and fall of Yosemite Valley’s flowers

Today’s visitor often hopes to see a bear, but very few people make the trip to Yosemite in hopes of seeing a flower open at sundown. In the early 1900s, it was the reverse. There were no bears in Yosemite Valley and when one did enter the Valley, most people thought it should be chased off or killed as soon as possible.

Meanwhile, they ranked wildflowers up there with El Capitan and Yosemite Falls as a must-see attraction. The wildflowers of Yosemite Valley inspired some of the earliest color photographs and the world’s first time-lapse movies of flowers. Indeed, time-lapse photography was virtually invented in Yosemite by Arthur Pillsbury, who held a photographic concession in the park from 1906 to 1922.

Among all the flowers of the park, the evening primrose was one of Pillsbury’s favorites. When he first came to Yosemite, he found entire meadows that would turn yellow as the flowers opened en masse, perhaps 100 per minute in some meadows. If our small patch gets 140 blossoms in 40 minutes, it does not seem out of the question that the huge displays in the meadows of Yosemite Valley might have seen 4000 blossoms in 40 minutes Given that some people report entire fields of them, it’s conceivable on the best nights there were 1,000 blossoms per minute at the peak.

Field of evening primroses in Yosemite Valley with Half Dome behind
From Arthur Pillsbury’s book, Picturing Miracles of Plant and Animal Life (Philadelphia: J. B. Lippincott Press, 1937). Sadly, I can only find black and white reproductions of Pillbury’s hand-tinted color photos, like this one of the evening primroses in Yosemite Valley, with Half Dome rising in the background. Consider the quality of this photo given that it was taking in the fading light of early evening with the technology available around 1910. We hope some day to see the original!

Wildflower Tourism at the Turn of the Twentieth Century

Wildflowers were such an integral part of the Yosemite experience that when the National Geographic Society ran an article about the park in their weekly Geographic News Bulletin (vol. 1, n. 9; 3 April 1922), they titled it, “The Park of a Thousand Flowers — Yosemite,” and noted that “Yosemite National Park is beloved especially by children because of its many flowers.”

Photocopy of the start of the Geographic News Bulletin article on Yosemite
The Park of a Thousand Flowers!

That publication was aimed at teachers and clearly some read it. Later that year, The Western Journal of Education (vol. 82, no. 7, p. 8-9) ran an article on “Yosemite National Park for the Educators” that described Yosemite Valley in these terms, highlighting the central importance of the evening primroses:

Decorate these walls with titanic structures — El Capitan, Half Dome, Sentinel Rock, Cathedral Spires, Cathedral Rocks — chiseled smooth as glass in many places, then stud these walls with foaming cataracts that flash in the sun, Yosemite Falls… Bridal Veil…. Carpet the meadows with Mariposa lilies and evening primroses and other blossoms which have made Yosemite known as the “Park of a Thousand Flowers.” This is Yosemite Valley.

Western Journal of Education, 1922

The “thousand flowers” referred to the thousand species of flowering plants, but writers also frequently mention the profusion of flowers on the Valley floor. In short, for the visitor of 1922, the flowers of Yosemite Valley rivaled El Capitan and Yosemite Falls in majesty.

The Decline of the Evening Primrose

And yet, by the time these publications came out in 1922, the golden age of the Yosemite Valley flowers was over. In the Handbook of Yosemite National Park from 1921, the great botanist Willis Jepson wrote regarding the evening primroses:

One of the remarkable sights of the upper reaches of the Valley in midsummer are the fields of tall yellow Evening Primroses… In favorable seasons the dry open fields about Yosemite are often yellow with these stately plants. Many of the finest groups, however, are now a thing of the past, due to the mowing of the meadows for wild hay.

Jepson, Handbook, p. 254

In her 1929 survey of flowers in Yosemite Valley, the naturalist Enid Michael noted that, “June of the year 1920 witnessed the last great bloom on the floor of the Valley” (Giddens and Heady, p. 25). Joseph Dixon, writing in 1934, said that in a survey of Yosemite Valley in the late 1920s, only six evening primrose plants had been found in the whole valley (Dixon, p. ?? [get page no. from copy in Yosemite Research Library]).

A few years later, the Wildflower Man of Yosemite himself, photographer Arthur Pillsbury, wrote:

Unhappily this Primrose is now almost extinct in the Yosemite meadows. The mowing machine took its toll and since it has been put on the protected list the deer have acquired a fondness for the leaves, not hesitating, either, at blossoms.

Pillsbury, Picturing, p. 54

What was still a highlight of a Yosemite trip in 1910 had all but disappeared by the 1920s.

The naturalists lamenting the loss of the evening primroses typically point to two factors: farming and deer. For most visitors, it’s surprising to think that Yosemite Valley was once home to several hayfields and pastures for horse and cattle, but was home to almost no deer, bear or coyotes. And yet, that was the situation around 1900.

Why were there so many flowers in 1900 and why were they all but gone by 1922?

Flowers in the Valley before 1900

After the glaciers receded, Yosemite Valley was a wetland or a lake. As the lands silted up and the waters receded, there is some evidence of ancient forest in Yosemite that was wiped from either rock slides or fires, either natural or manmade (Gibbens and Heady, p. 8-9).

For at least a few thousand years, inhabitants of Yosemite Valley set fire to the meadows, typically in the autumn. This made it easier to harvest fallen acorns and promoted the growth of plants with edible bulbs and tubers. Many of the common flowers we know today were prized as root crops, like Elegant Brodiaea (Brodiaea elegans), Blue Dicks (Dichelostemma capitatum), Mariposa Lilies (various Calochortus species), and many more. See the wonderful article by M. Kat Anderson and Frank K. Lake on the various “geophytes” (roughly speaking, “root crops”) prized and eaten traditionally in California.

The meadows were also important for plants such as dogbane (Apocynum cannabinum) that was not eaten, but was used for making twine and therefore an essential material for the residents of Yosemite Valley. The Valley was sometimes described as “swampy” and we know that numerous changes from blasting the recessional moraine near El Capitan to building roads began to dry out the meadows (Gibbens and Heady, p. 8 and passim). So it’s quite likely that swampy crops like onion were common, though they are rare today (there are local varieties of onion that like dry soil, some of which grow a short distance from our home, but the largest onions in the area are all wetland species).

This burning also kept tree encroachment from choking the meadows. As soon as the burning stopped, the size the of the meadows started to decrease and the European-American methods of controlling the brush through cutting was labor intensive and much less effective. A survey in 1868 found that there was 745 acres of meadow in Yosemite Valley. By 1937, only 327 acres of meadow remained (Gibbens and Heady, p. 24).

It also appears that the Ahwahneechee used fire to hunt the deer in Yosemite Valley, and probably elsewhere (Ernst, p. 39). Finally, oral tales speak of the Ahwahneechee going up to the Valley rim to hunt for deer, presumably because deer were not abundant on the Valley floor due to hunting.

All of this combined to create a Valley floor that had much more meadow and much less undergrowth than we’re used to. Also, those meadows may have been wetter and they were certainly burned more often. And finally, there were no grazing animals there, either wild or domestic. All of that probably means there were a lot more flowers than we’re used to, but we mostly know about the species that were used for food, and precious little even about those.

Yosemite Valley from Invasion to National Park

After the Ahwahneechee attacked a couple of trading posts, the Mariposa Battalion invaded Yosemite Valley in 1851 and forced the Ahwahneechee out for the first time. The tribe returned that winter, but most were forced out definitively in 1852. Though a small number resided in the Valley into the 1960s, they effectively lost control of their lands and therefore the meadow burning stopped in the 1850s.

In 1855, Just four years after the initial invasion by the Mariposa Battalion, an early tourist wrote that Valley was rich with berries, in particular strawberries:

The wag of our party said that any man who would find three feet square in a space of six hundred acres, where we encamped, that did not have the strawberry on it, should have the pleasure of shooting through his hat. The search was made for the space; but our friend says his hat will never have a hole through it from this proposition.

Reprinted in Browing, p. 219.

In 1864, Yosemite Valley became a California state park, but it was managed much less actively than today. Despite its status as a park, settlers and business people soon began grazing cattle and horses and plowing for crops. At least 20 acres of El Capitan meadow was plowed and sown with fodder for horses and cattle. Many other meadows were plowed or used as pasture for both horses and cattle. By 1887, 150 acres of Stoneman Meadow was under active cultivation. People began to complain and in 1890 new rules were passed to reduce farming in Yosemite Valley. Nevertheless, the government plowed and planted Ahwahnee Meadow from 1910 to 1914. Other meadows were not plowed, but they were mowed for “wild hay” as late as 1924 (Gibbens and Heady, pp. 4, 21-22).

Man with a plow and team of two horses with Half Dome in the background
Photo of US government electrician Sam Cookson plowing Ahwahnee Meadow in 1911 or 1912. Public domain photo from NPS collection.

Despite this history of plowing and mowing, Yosemite Valley nevertheless had breathtaking displays of flowers, with the evening primrose as one of the stars, perhaps the star of the show.

How is it, then, that the evening primroses thrived in the presence of mowing, and yet disappeared about the time mowing stopped?

Naturalists of the time agree on two things. First, before the mowing ended, it moved to new locations and wiped out some of the best surviving collections of flowers. Second, the deer population boomed. By the time the plowing and mowing stopped, the number of deer was sufficient, as it is now, to all but eliminate the evening primrose from the valley.

Yosemite Valley: Death Trap to Animals
(Or: Why the Deer Didn’t Eat All the Flowers in 1900)

We think of deer as numerous and ubiquitous in Yosemite Valley, but it wasn’t always the case. From the late 1800s until 1906 the deer, along with most large animals, were hunted to extinction on the valley floor.

Though the national park had been created in 1890, Yosemite Valley remained a state park under state management. Rules against hunting were widely ignored. In 1905, Yosemite Valley became part of Yosemite National Park. The next year, the U.S. Army, who managed the larger national park, took over management of Yosemite Valley as well. In his 1906 report, Acting Superintendent Major Harry Benson reported to Washington about the conditions he found on taking charge of the Valley:

The Yosemite Valley itself has, during recent years, been a death trap to all game that was unfortunate enough to enter it. Practically every person living in the valley kept a rifle, shotgun, and revolver, and any animal or bird that was unfortunate enough to enter the valley was immediately pursued by the entire contingent, and either captured or killed. A bear pen constructed about three years ago was found by me within 400 yards of the Sentinel Hotel.

During the early part of September two bears entered the valley, causing great consternation among those people who had been living here for some time, and they all seemed to think that these bears should at once be pursued and driven out.

Benson, Report, p. 10.

To make matters worse, during those years, the army only managed the park from May through October. The rest of the year, only two rangers oversaw the entire park. Benson noted that, as the two rangers did little patrolling, “the game scarcely receives any protection from them.”

Those conditions were terrible for the deer, but marvelous for flowers. The valley floor was reputed to be white with camas lily in the early season and yellow with evening primrose in July. It was during this period that Arthur Pillsbury took his famous hand-tinted photos of evening primroses and, later, his time-lapse movies of them opening.

As late as 1908, Acting Superintendent Benson was still worried about the deer population and intensive hunting. But from 1909 on, the Acting Superintendents repeated every year that the deer population was increasing. This hurt, above all, the evening primroses. As we have found in our yard, the deer seem to love this plant as much as we do. Still, the deer were not so numerous as to kill them all off. In his 1910 book, The Yosemite Valley, Galen Clark noted that the evening primrose was “very common in Yosemite.”

After about 1910, the evening primroses faced greater pressure from both deer and mowing. Initially, the rise of the automobile reduced the need to grow hay and graze the meadows (Gibbens and Heady, p. 5). At the same time, the burgeoning tourist trade in Yosemite required fresh milk and meat. Fresh milk and meat in the days before refrigerator trucks required cattle. And cattle needed hay. Despite the predations of the plowman and the deer, however, the flower remained an attraction. The July 31, 1922, issue of Yosemite Nature Notes still suggested that visitors go out into the meadows to watch the evening primroses open.

Sounding the Alarm in the 1920s

By the 1920s naturalists in the park had sounded the alarm: the flowers were disappearing. In response, the park service and the concessioner made various attempts to hold onto the tradition of Yosemite’s great flower displays. In the early 1920s, Yosemite’s Curry Company tried to plant wildflower gardens in Curry Village with poor results: “Although plants commonly grazed by deer were avoided, the project was abandoned after three years of unsuccessful attempts to keep out the deer.” (McLelland, Chapter 4, section “Grounds of the Concessionaires”).

During the planning of the Ahwahnee Hotel, a 1927 memo called for a “plant refuge” around the hotel because, “It is well remembered that the meadow many years ago were filled with evening primroses” and other plants (McClelland, Chapter IV, my emphasis). Note that already in 1927, people thought of the spectacular blooms as something that happened “many years ago.”

After a rough start, the plants were fenced in to protect them from deer and elk, the latter having been introduced into Yosemite. In 1929, Horace Albright, the new director of the National Park Service, commented that the Ahwahnee plant refuge was “‘the only place in the valley where native flowers’ could ‘be seen in any profusion’” (ibid.). Around 2010, as I was relating some of this history to long-time ranger Bob Roney, it sparked a memory. He told me that the evening primroses were still there in the early 1970s and, though he didn’t now the history, he remembered watching them open from a seat by the window in the Ahwahnee Dining Room the night he proposed to his wife.

Meanwhile, the park service began maintaining flower exhibits behind the new museum, first with cut flowers gathered from around the park and, beginning in 1929, with a live garden protected from deer. The garden expanded under the direction of naturalist-ranger Enid Michael. In 1935, evening primrose was planted. This collection of now-rare flowers “became the object of popular evening walks” (McClelland, Chapter IV and Chapter VI).

During my ranger days, I would occasionally encounter long-time park visitors who remembered going to the museum garden in the evening to see the evening primroses open. In 1941, Enid Michael wrote an article for Yosemite Nature Notes (vol. XX, no. 4, p. 30-31) on the “Guests of the Evening Primroses,” about the carpenter bees and sphinx moths. She still waxed poetic about the show the flowers put on as the sun goes down, but she now located it in the Museum Garden, not in the meadows of Yosemite Valley as the author of the 1922 article had done.

Evening Primroses Today

Over time, even the Museum Garden and the Ahwahnee Hotel “plant refuge” disappeared. Now, only visitors with a sharp eye and good timing will find evening primrose blooming in Yosemite Valley. Every year there is at least one place in the disturbed soil along the roads in the Valley that you can find an evening primrose that has survived the deer. By far the best collection grows along the road just east of Tioga Pass. It is perhaps the last place where, on a good night, you can see hundreds of plants produce perhaps 1000 blossoms. The next best place is our house in a year when we succeed in keeping the deer away.

When we first found evening primroses in bloom near the house, we did not know most of this history. We had seen them by the chapel and had noticed that they were there when we drove by in the morning, but not in the afternoon. Though it was on our list of things to do, we had not actually sat and watched one open. It wasn’t until our first crop came in at our house that we sat and watched and witnessed the magic of the blossom opening. That started our education and our desire to create, if possible, a small refuge of evening primrose, at least in those years where we do not lose our running battle with the deer!

Humans, Nature and Evening Primroses

The story of the evening primrose in Yosemite raises some interesting questions. When I first came to Yosemite in 1985, I imagined I was walking through a landscape preserved from time immemorial just as it always had been. Of course, even the most superficial reflection reveals that to be untrue — a landscape formed by the Big Bang, plate tectonics and glaciers has no “original” form outside the Singularity. Still, I imagined that it had changed little over the last few hundred years, setting aside a few roads, trails and hotels of course.

The understanding that the place I thought of as stable could have changed so much in 150 years took a process of education. Only over time did I realize that large patches of the Valley are almost entirely populated with cheatgrass (Bromus tectorum), which did not even exist in North America until the late 1800s. The common mullein (Verbascum thapsus), which grows widely throughout the Valley, was brought over by Europeans and planted as a medicinal (for stomach ailments). And many of the Valley meadows are full of Kentucky Bluegrass which, despite it’s name, is a Eurasian species, not a native of Kentucky.

All of that makes me ask what it means to refer to a place as “natural”? Is Yosemite today, with its roads, hotels, restaurants, exotic Eurasian plants and huge deer population, natural? Was the Yosemite of 1906, with no deer, plowed meadows and a magnificent show of evening primroses in unplowed areas, natural? Was the Yosemite of 1800, with double the meadow and a tiny fraction of the undergrowth that we know today thanks to annual fires set by the Ahwahneechee, natural? Once you ask that question, it becomes clear that the simple word natural is an inexact label for an extremely slippery concept.

Those are not questions I try to answer, since better minds than mine have devoted entire books to wrestling with those questions. Instead, on the question of what is human and what is natural, I’ll just end with a quote from historian William Cronon:

If wilderness can do this—if it can help us perceive and respect a nature we had forgotten to recognize as natural—then it will become part of the solution to our environmental dilemmas rather than part of the problem. This will only happen, however, if we abandon the dualism that sees the tree in the garden as artificial—completely fallen and unnatural—and the tree in the wilderness as natural—completely pristine and wild. Both trees in some ultimate sense are wild; both in a practical sense now depend on our management and care. We are responsible for both, even though we can claim credit for neither.

Cronon, The Trouble with Wilderness

And that is why I have avoided calling the evening primroses that grow near our house “our plants.” We feel responsible for them, but can’t claim credit. They are their own plants.


Many sources are either cited in full or linked in the text. The sources that are mentioned just by author name are here given in full: