Cactus-type dahlias grown by John Spangenberg of Damascus, Md., await staging at the National Capital Dahlia Society’s annual show at Brookside Gardens in Wheaton on Sept. 28. (Adrian Higgins/The Washington Post)

I was standing along the Alexandria waterfront a couple of years ago when a Spanish galleon showed up, proving once again that if you wait long enough, everything comes full circle.

This is especially true in the gardening world. Houseplants, embraced by hirsute, plaid-draped baby boomers in the 1970s, fell into obscurity before being rescued in this century by millennials.

Succulents were once the domain of rock-garden enthusiasts — there is no more esoteric a subset of gardeners — but are now an essential part of contemporary urban life. Old garden roses are back and so is kale. What will be next? Carnations, snapdragons, Kentucky bluegrass? The possibilities are endless.

The dahlia, a tender perennial from the high plains of Mexico, sent Europeans into a frenzy of delight when it showed up in the Old World, quite possibly aboard Spanish galleons. The Empress Joséphine, known for her love of roses, was crazy, too, for dahlias. The European mania led to the breeding of a wide range of dahlias, in color, form and size, and soon growers were classifying this cornucopia so that they could do what all flower fanciers of a simpler age liked to do: Show them off. Dahlia shows proved to the public what an amazing flower the dahlia had become in the hands of devoted hobbyists.

Dahlias also have had a long presence in the garden, the small ones tucked between other perennials, the tall ones staked as sentinels in the border.

An entry features small dahlias known as mignon singles. (Adrian Higgins/The Washington Post)

In our own time, when perennials and grasses have come to the fore, dahlias seemed to recede into the past, like lavender water, pedal cars and mahogany wardrobes. Now we have come to see that few other flowers are so luxuriant in their color, which includes shades of orange, red, burgundy and yellow. The darker the hue, the more intense it seems to be.

The cut-flower world, inherently photogenic and made for social media, has been given an enormous boost on photo-driven digital platforms in recent years. Nothing in October is as vivid as a bouquet of dahlias. Dahlias are back.

But in one sense, they never left. The other Friday night, I found myself at Brookside Gardens in Wheaton, Md., with a handful of dahlia fanciers getting ready for the National Capital Dahlia Society’s annual show. Its 83rd annual show. Most of the growers were getting on a bit, but the mood was cheerful, filled with anticipation of the weekend, and not in the least moribund (if you discount the wall plaques and photos of four members who had passed on since the last show).

The youngest exhibitor I found was Christa Carignan, 46. She put 20 plants in her small Rockville garden in May, in raised beds originally built for vegetables. She has been hitting the dahlia shows in Maryland — Brookside was her fourth — after seeing show dahlias for the first time last year. This is always an eye-opener to the novice because of the unexpected sizes and forms, including ball types that look like paper Christmas tree ornaments, spiky “cactus” blooms and those as wide as your head. (The American Dahlia Society recognizes 21 forms in sizes from less than two inches across to more than 10 inches.)

For Carignan, the dahlias are an extension of the wildflower-inspired arrangements she has been making, ones that are popular with gardeners of her generation and younger. “I share my dahlias on Facebook with friends and family,” she said, “People my age and younger think it’s awesome.”

An entry of seven blooms in the container section. (Adrian Higgins/The Washington Post)

Serious hobbyists might have more than 200 plants in their gardens, growing in carefully prepared beds and supported by horizontally strung netting. It’s more farming than gardening. If you grow five of one variety instead of one, the chances are good you will have a perfectly formed and pristine flower stem at show time. The rejects might be too slug-eaten or at the wrong stage of development. If the center of an otherwise immaculate dahlia is open — “blown” in grower parlance — you might as well stay home.

Another exhibitor, Bernadette Rager, of Olney, Md., could be seen cooing over her blood-red, decorative-type dahlia named Black Beauty. I asked her how much time she devotes to her dahlias, and the answer gave some clues as to why fanciers tend to wait until later in life to tackle this flower. (Rager is retired from the Montgomery County school system.)

“I spend an hour a day from April to the first frost. And then you have to put [the tubers] away in the winter and check them every week” for rotting in storage. “All summer, you can’t go on vacation because you can’t leave them.”

This growing season brought a burden unlike most others. Dahlias like moisture but also good drainage, bright light and cooler temperatures, especially at night. This summer in Washington was about as hot, wet, cloudy and soggy as they come, with about 20 more inches of rain than usual. This caused all sorts of problems for dahlia growers. My own were slow to get established, lacked vigor, flopped and were stinting in flower. Most buds failed to develop and simply rotted.

As John Spangenberg of Damascus, Md., was readying his blooms for the show, he remained upbeat despite it all. “I probably lost a quarter of my garden in the spring,” he said. “I have never had a year as bad. My garden is finally starting to show color” as fresh buds make it to maturity. He enters so many dahlias, many his own seedling hybrids, that he could only give a round number (100).

Dahlia exhibitors may be a small band of aging brothers and sisters, but no calamity seems too daunting. “If we just had five blooms, we would still go out and judge them,” Spangenberg said. “The show must go on.”

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