Bridget Maginn passed her 90th birthday years ago, but her eyes lit up like a child’s as she made her way through the profusion of red and green — and pink and cream and apricot — plants on display at the Howard P. Rawlings Conservatory.

She had dropped in on the annual poinsettia show at the Victorian-era glass house in Druid Hill Park, as she does every winter.

Maginn, a retired teacher and plant aficionado, said she never feels her Yuletide has begun until she sees the sprightly shrubs.

“It’s such a lovely way of bringing you into the season,” she said, glancing up from a cream-and-scarlet version of the popular holiday plant. “You see this brilliant red, and you simply know it’s Christmas.”

The show has been a fixture on the local holiday scene since 1948 — which would make this year its 70th iteration, had the facility not been closed for a $4.4 million renovation from 2002 to 2004.

However you count, the conservatory has hosted the annual display and sale long enough to make it a regular stop for generations of families — locals of all ages whose holiday custom is to come by and pose for pictures, purchase a poinsettia or two, or simply step into the pleasantly steamy climes inside the building as a respite from the cold.

“It’s definitely a Baltimore tradition,” says Kate Blom, director of the conservatory, which is run by the city’s Department ofRecreation and Parks. “Parents bring their kids, and when they grow up, they bring their kids.

“We have families who visit every year to take photos for their Christmas cards or to visit Santa on the day he’s here. It may be the only day they visit us, but they make sure to come.”

It has been about 60 years since poinsettias — flowering plants of the euphorbiafamily, originally native to Mexico and Central America — became enmeshed in the American mind as a symbol of the nation’s favorite holiday.

A Mexican fable from the 1500s holds that a young girl who was too poor to bring a gift to a Christmas celebration was told by an angel to visit the weeds by the side of a road, where she saw a green plant transform into a scarlet poinsettia.

By the 17th century, Franciscan monks in Mexico were using the plants as part of their Nativity processions.

But it wasn’tuntil 1825 that Joel Roberts Poinsett, the first American ambassador to Mexico, fell in love with the plants, which grow in the wild as shaggy shrubs or trees, and transplanted some to his own farm in South Carolina. And it wasn’t until the early 20th century that a German immigrant family, the Eckes, began breeding brighter, more compact, longer-lasting varieties at their ranch in Los Angeles.

A third-generation member of that family, Paul Ecke Jr., decided to raise the shrubs’ profile by donating them for use in the layouts of popular women’s magazines at Christmas and, after the advent of color television, for display on the sets of Bob Hope Christmas specials, the “Tonight” show and other widely viewed programs.

A subliminal connection was formed: Poinsettias only bloom for six or seven weeks a year, but still they overtook chrysanthemums as the No. 1-selling potted plant in the U.S. by the 1980s, according to the 1998 book "Poinsettias, the December Flower," by Christine Anderson and Terry Tischer.

They now represent a $200 million a year industry.

Scott Ritchie is the greenhouse supervisor at Baltimore’sCylburn Arboretum, where he leads a small team of gardeners who spend five months a year growing the nearly 3,000 poinsettias that are transported to the conservatory and put on display each December.

He finds it funny to know that a project he works on so carefully has roots in TV culture — “It all started with the ‘Ed Sullivan Show,’ ” he laughs — but the labors are serious business.

Raising poinsettias is a complex process, he says, and displaying them a fun artistic challenge.

It starts in the summer, when the Cylburn gardeners receive thousands of cuttings from growers across the United States.

Ritchie works with Blom and her team of ten professionals and several dozen volunteers to choose from among the more than 100 varieties of poinsettia now available. The include staples such as the Freedom breed, one of the Ecke family’s first varieties, to Winter Rose, Cinnamon Star and newer breeds such as the Princettia.

It’s actually the leaves of the plant, not petals, that are so colorful, Ritchie says.

Freedom comes in red, white or a popular mottled white-and-red blend known as Jingle Bells, which happens to have been first cultivated in the greenhouse of Baltimore County horticulturist John Fantom in 1971.

Winter Rose, with its small, crinkly leaves, can be grown in red, white or cream; Cinnamon Star is a “light dusty orange with pink undertones” that “comes off as a cinnamon color,” Ritchie says.

Ritchie and Blom choose a different combination each year, adding new breeds and dropping others to foster variety and heighten the visual impact for guests.

The master gardener’s team at Cylburn spends the next several months following the exacting regimen poinsettias require: providing 12 hours of light and 12 hours of total darkness per day, pinching off selected buds to shape the plant’s growth, adding incrementally to the spaces between them as they grow.

Some growers must customize their greenhouses, painting the glass panes to ensure the required total darkness when it’s needed — even a little too much light can delay the arrival of color. Most go to great pains to maintain the ideal temperature.

For a city site, Cylburn is ideal for growing poinsettias — the greenhouses are on an isolated hilltop far from streetlights, which makes for laboratory-like conditions.

The results start coming in the day after Thanksgiving, when the first of the plants are relocated to the conservatory and arranged.

Blom and her group choose a theme for each year’s display, usually one based on a work of children’s literature. The volunteers spend several months getting that part of the display ready.

Past themes have included Alice in Wonderland, a Maurice Sendak sendup called “Where the Wild Things Grow,” and “It’s a Wonderful Life,” each festooned with the seasonal plants.

This year’s theme is “Through the Wardrobe: The Magical Gardens of Narnia,” a tableau for children based on the books by C.S. Lewis.

Guests enter through a makeshift closet, happen on a life-sized Queen of Narnia — the white witch who banishes Christmas, turning Narnia’s creatures to stone — and encounter a swan and a unicorn made of pampas grass, among other elaborate props.

A Narnia-themed scavenger hunt will take young visitors to every room.

Visitors will also see the conservatory’s traditional 10-foot Christmas “tree” made of poinsettia plants in the conservatory’s oldest chamber, the Palm House.

The display will remain open through Dec. 31, closing only on Monday and Tuesday. About a third of the poinsettias are for sale, for $5, $7 or $10, depending on the size.

The show has drawn the conservatory’s usual holiday numbers so far — about 30 guests per day.

Many are the children Blom says she hopes will one day return as adults, as Maginn does, sharing the tradition with their own kids and keeping it alive in the city for another 70 years.

“There’s something about poinsettias and Christmas,” she says.

jonpitts@baltsun.com

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