In 1901, Charles George Wyatt discussed the new cactus dahlia at the Royal Horticultural Society in England, noting that it seemed scarcely possible that within the past 20 years this entirely new form of the dahlia, which had been a favorite with gardeners for 60 or 70 years, "could be so transformed into the totally different character represented by a really good Cactus Dahlia." Wyatt went on to claim that all the best of the new cactus dahlias were hybridized by the British, "foreign introductions as yet falling very far short of the high standard necessary for approval."
The cactus dahlia was at the time widely believed to have developed from the Dahlia Juarezii, a dahlia introduced into Europe from Mexico in the 1870s, but Wyatt maintained that the cactus dahlia was likely the offspring of the aptly named Dahlia variabilis, which was introduced to Europe almost a century earlier. Whatever the case, the cactus dahlia has rolled florets that radiate from the center of the blossom in a uniform arrangement; it has been described variously as resembling the cactus, fireworks, and sea urchins.
On Cactus Dahlia Day at the exposition, August 28, 1909, the Washington State Building was decorated with thousands of cactus dahlias "in almost every conceivable color," boasted a daily AYP publication. A committee headed by UW professor Edmund Meany chose the dahlia as the official flower for the event because of its novelty and because dahlias grow well and have a long blooming season in the Northwest. Organizers hoped that the cactus dahlia would become to Seattle what the rose was to Portland, the anchor for an annual festival. While that didn't happen, the cactus dahlia certainly gained a foothold in the Pacific Northwest garden scene, with hundreds of people buying and planting dahlias in succeeding decades.
Cactus Dahlia Day in 1909 began with a flower parade of girls and young women, dressed in white, garlanded with dahlias, and carrying cactus dahlia bouquets, who followed the AYP Band from the exposition's main gate to the state building. When they had arranged themselves on the main staircase of the Washington State Building, they sang "Where the Cactus Dahlia's Blooming," a song commissioned for the exposition with words by Rene Bronner and music by Seattle composer Frederick Benjamin. The floral choir chorused,
"When the Cactus Dahlia's blooming,
'Neath the sunny Western sky,
Where the lands are lovely booming
And the multitudes go by,
Then the dreams of old Seattle,
To the world will brightly shine
Where the Cactus Dahlia's blooming
In the year of nineteen-nine."
Throughout the building, tables held vases of dahlias offered by more than 35 exhibitors who brought flowers for judging. Professor Meany spoke at the closing of the program. "Proclaim, ye heralds of the brilliant floral train. Proclaim this day the Cactus Dahlia's reign." It was a relatively short reign. The Seattle City Council declined making the cactus dahlia the city's official flower and didn't establish the annual festival Meany had hoped for. But that year, the Washington Women's Cook Book, published by the Washington Equal Suffrage Association, specified that cactus dahlias be used to decorate the dining table for a "Washington State Dinner."