Gardening tips: Growing and storing spectacular dahlias

Published on Wed, Aug 27, 2014
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Dahlias are a signature flower here in the Northwest. The beautiful blooms grow bigger and better in our temperate northwestern climate than anywhere else in the world, allowing the huge variety of forms and colors to truly come alive. 

But while the climate here gives plants the greatest opportunity to thrive, keeping the tubers alive over the winter can be a tricky prospect. The thin-skinned tubers can be killed by sudden frost if they’re not properly stored. Fortunately, the Whatcom County Dahlia Society has a countywide membership with years of experience, ready to lend a hand. 

Paul Bloomquist is president of the Whatcom County Dahlia Society, and has been a member of the club for nearly 25 years. 
He said the sheer variety of the plants is part of the appeal for him. 

“You can find flowers that are 3/4 inch across at full bloom, and you can find others that are almost 24 inches across,” Bloomquist said. “There are more than 20 different forms, and they can range in height from 12 inches to over 10 feet. There’s just a remarkable variety.”

The society has been meeting regularly since 1983, hosting monthly meetings for aficionados of the colorful flowers and offering advice to aspiring gardeners. At their monthly meetings at the Laurel Grange in Lynden, members from Blaine, Birch Bay, Bellingham, Ferndale and nearly everywhere else in the county trade tips on growing the best dahlias possible.

The group is currently preparing for two big expositions, the 2014 American Dahlia Society national show, taking place in Tacoma this Labor Day weekend, and the club’s own dahlia show, to be held in Bloedel-Donovan Park in Bellingham on Saturday and Sunday, September 6 and 7. The club’s dahlia show will feature a variety of over 2,000 flowers, with a huge selection of colors, forms and heights. 

Bloomquist says most gardeners make two big mistakes when it comes to planting dahlias: they plant them too early and store them improperly when the weather gets cold. 

Late spring to early summer is the ideal time to plant dahlias. The plants thrive on sunlight and moist, moderate temperatures, so gardeners should plant their dahlias in sunny spots. Most places in Whatcom County get enough water to naturally sustain dahlia tubers when they are still in the ground, but once the stalks start to appear above the soil, the flowers require some heavier watering. Generally, a deep watering of about 30 minutes, two to three times each week, will be sufficient. This, coupled with medium amounts of a low-nitrogen fertilizer, will help the flowers bloom. 

When the weather gets cold, dahlia gardeners will have to choose between leaving their tubers in the ground or digging them up and storing them for the winter. Winters in Whatcom County are fairly mild, and deep freezes are rare, but Bloomquist recommends digging and storing tubers to keep them coming back strong each spring. 

“In this area, you need to dig them,” Bloomquist said. “You just have to be sure not to store them too wet or too dry.”

According to an article on by landscape expert David Beaulieu, the best time to dig up the plants is approximately one week after the blooms begin to appear withered. The flowers may seem dead, but the tuber below the surface is very much alive, and storing the nutrients it needs to bloom again in the spring. 

Once the week has passed, carefully dig up the dahlias with a pitchfork to preserve the sometimes-large tubers. Remove the dirt from the tubers and then hang them out to dry for one or two weeks, being careful to keep the tubers out of direct sunlight. Finally, prepare a container with lightly moistened peat moss, bury the tubers within and store the container in a cool, dry place. The ideal temperature for storing the tubers is below 50° F but higher than freezing. 

If all goes well, you should be able to replant the tubers in the spring. If not, however, the Whatcom County Dahlia Society hosts an annual tuber sale the first Saturday of every April to help your garden get back on track. 

For more information on the Whatcom County Dahlia Society, visit the society’s website at