Mary Ann O’Brien will do everything it takes in the fall to ensure she has glorious dahlias, the Dom Perignon of her gardens, in the spring.

On a chilly November day after the first frost, O’Brien was on her knees digging tubers from more than 25 different dahlia cultivars to store for the winter. After they dry out in the garage for a few days, she slices and divides each tuber, multiplying the number she’ll have to plant in spring.

“I make sure to get a piece of stem with each one,” she said. Then O’Brien rolls the dozens of tubers in plastic wrap, stands them vertically in cardboard boxes with ends open, and sprinkles the tubers with vermiculite. Lastly, she records the color or variety name on index cards and stores them in a big cooler at 40 to 50 degrees.

It’s tedious, hard work, she admitted. “But by August, the blooms are so showy you can’t take your eyes off of them. Dahlias never disappoint.”

The showstopping dinner-plate-sized ‘Zorro’ and ‘Weston Spanish Dancer’ are only a small part of O’Brien’s sprawling gardenscapes, which she designed, planted and tends with her husband, Duane Miller, on their Stillwater property, where they’ve lived for more than 20 years.

The couple built their walkout rambler in 1993 on a 1-acre lot abutting the Indian Hills Golf Course. Even before the builder broke ground, the longtime passionate growers were plotting where they would dig their gardens for the best sun exposure. Fortunately, excavation for the walkout created two big berms, resulting in visually interesting rolling terrain for the garden beds.

The couple amended the hard clay soil with truckloads of black dirt and launched what would become a two-decade labor of love.

O’Brien and Miller consider their gardens “evolutionary” because the landscape was shaped over time with flower beds, bushes and trees, as well as countless boulders from a quarry in Wisconsin.

“The fun part was selecting the plants and the trial-and-error of successfully growing them,” said O’Brien.

Today the thoughtfully planned O’Brien/Miller creation boasts season-long blooms — from daffodils and tulips in the spring, to dahlias and zinnias in late fall. ‘William Baffin’ roses climb a white wooden arbor marking the main entrance to annual and perennial plantings. Miller laid the curving flagstone pathway using Colorado red rock to contrast the waves of green foliage.

The path guides you from snapdragons and Russian sage to the “Chinese garden” adorned with a stern terra cotta warrior the couple found on a trip to China. Nearby, a hedge of hardy shrub roses has long replaced Miller’s once-prized hybrid teas. “They were too much work in this climate,” he said. “We had to tip 40 rose bushes in the fall, and each season they lose some of their robust quality.”

Junk-shop find

“Stretch,” a rusty giraffe sculpture, towers over clumps of hosta and dogwood shrubs for a touch of whimsy. The couple spied the 7-foot-tall metal giraffe in a Phoenix junk shop. “We could picture him eating the birch tree leaves,” said Miller. So they strapped him to a trailer and drove him home to Minnesota.

At summer’s end, the gardeners are rewarded with fireworks of Technicolor zinnias, which they grow from seed. “I like to intermix dahlias with ‘State Fair’ zinnias for bold color from August until the frost,” said O’Brien.

Some of her plant choices also are dictated by her busy wedding floral business, Keswick Gardens of Stillwater. For her wedding bouquets, O’Brien snips plants from her beds, such as blue lisianthus and sea holly. “I nestle a rose in the middle of pachysandra for corsages,” she said.

O’Brien’s overall garden design is driven by a desire to create informal winding pathways guiding the garden experience. “I like a garden you can stroll through,” she said. “With visual separation to enjoy each plant — and space to tend it.”

And she intentionally planted the eye-catching dahlias that people can see from the cul-de-sac to invite them to enter for a closer look. Golfers from Indian Hills can see them, too. When O’Brien is weeding, “they drive up in their cart and tell me it’s the best part of the 17th hole,” she said.

But, unfortunately, the golf course grass attracts swarms of Japanese beetles that munch on O’Brien’s tenderly cultivated flowers. Every day, she inspects plants for the destructive insects. “See this one on the dahlia,” she said, and flicked the beetle into a bucket of soapy water. “They are relentless.”

Finally, flagstone steps lead to a tranquil waterfall flowing into a pond bordered by cool blue-gray boulders. Miller designed the water feature, and a landscape company installed the 300-gallon pond and 25-foot-long fall. “We wanted it to look natural, like it was coming from behind the trees,” said Miller.

One regret was that they planted a blue spruce above the pond; the tree drops needles and makes it difficult to keep the water clean. But the couple love the playful frog figurines perched among ferns and sedum on the rocks. The frogs were given to them by friends over the years.

The partners in planting, who now are both retired, each play an integral role in their gardens’ success. Miller is the “grunt” who hauls rocks and digs holes. “I don’t have the passion for picking plants,” said Miller. “But I’m proud of what Mary Ann has accomplished.”

In spring, O’Brien especially feels a spiritual connection to the shoots emerging from the earth. “The flowers are so dramatic, exciting and wonderful,” she said. “What could be more hopeful than spring?”