They're also beloved for their blissfully long flowering period, which starts in July and continues until the first hard frost, usually in November.
Enjoying that bloom time isn't as easy, however, if your plants start to fall over because they're so tall, especially when the autumn rains weigh them down.
There is a solution: Staking.
Good staking, which is essential for taller varieties, starts in spring before you put your dahlia tubers in the ground, according to Hills Collins, a longtime member of the Snohomish County Dahlia Society, which is hosting its annual flower show this weekend in Everett.
Collins, who has grown dahlias since the mid-1990s, uses metal rebar, cut into six-foot stakes, thrust one to two feet into the ground, spaced about 30 inches apart.
Rebar stakes, available in various thicknesses, are easier to pound into the ground than wooden stakes, which can easily crack and, after a few seasons, rot.
Collins uses a three-pound maul to tap rebar stakes into place if the soil is rocky or resistant.
Then he plants two tubers -- the potatolike bulbs that produce dahlias -- next to each stake with the eye ends of the tubers almost touching the stake.
Each eye will produce the plant's main stem, which eventually can be tied to the stake with green biodegradeable baler twine.
We know what you're thinking: "I don't want to dig and store my dahlia bulbs. That's a lot of work!"
We hear you. But at least you don't have 330 plants to dig up like Collins.
There are good reasons to unearth tubers every fall, including successful staking and tidy plants, rather than sprawling, falling shrubs.
Dahlias, in order to produce their most fabulous and largest blooms, need to be divided every three years.
Underground, tubers multiply and grow large. Like many perennials, however, plant performance eventually starts to suffer if they are not divided and rejuvenated.
"The blooms will start getting smaller," Collins said. "They get weaker."
Dividing also gives you extra tubers to share with friends or use in your own garden for even more blooms.
If you don't dig, you can always follow Collins' method for staking his dahlia seedlings, which he grows more closely together in large quantities: Rather than putting a stake next to each plant, Collins puts stakes around the edges of the planting area and ties the twine around the whole bushy mess.
Another trick for keeping your dahlia-cutting garden tidy is disbudding.
Disbudding is when you pinch off the two side flower buds that form next to the central flower bud.
You do this when the side buds are small, about the size of peas, almost hidden in the crotches between each main stem and its leaves.
Snohomish County Dahlia Society members and professional growers disbud all the time, not just because it makes the central flower grow bigger and more beautiful, but also because it gives each flower a longer, more presentable flower stem.
Longer stems aren't just good for dahlia shows, they're also ideal for cut flowers at home.
If you want so-called dinner plate dahlias -- more than 12 inches in diameter -- disbudding is just the trick for you because it directs each main stem's energy into one central flower instead of three.
Collins recommends doing disbudding in cool weather, ideally early in the morning or in the evening when the dahlia plants are crisp with moisture and the buds snap off easily. Midday heat makes the buds rubbery, which can lead to tearing and bad breaks.
Though disbudding will give you fewer flowers overall, it won't hurt the plants a bit.
In fact, each remaining flower will have more room to grow. And more flowers will keep coming until the first hard frost.
Collins, 67, of Marysville, said this year's weather has been a mixed bag for dahlias. Though the cool, wet spring gave them a slow start, the subsequent overcast days of summer have been good for preserving their vibrant colors.
"It's amazing, once they start growing, how fast they grow," he said. "I'm surprised I have as many blooms as I do. They just, all of the sudden, took off."
You don't have to join the local dahlia society to become an expert in these most enchanting flowers.
This weekend's show will include more than 2,000 blooms entered for competition, a dahlia photography competition and advice from local experts, including handouts and month-by-month guidebooks for dahlia care in the maritime Northwest.
Collins actually fell in love with dahlias in 1998 at the annual show, held at Floral Hall at Forest Park in Everett.
"I walked in that hall and I thought, 'I want to know how to grow these,'" Collins said. "They're not as hard to grow as people think."
What: The Snohomish County Dahlia Society present its 102nd annual dahlia show, featuring more than 2,000 blooms entered for competition, a dahlia photography competition, and advice and handouts on growing dahlias.
When: 1 to 6 p.m. Saturday and 10 a.m. to 4 p.m. Sunday.
Where: Floral Hall, Forest Park, 802 E. Mukilteo Blvd., Everett.
Information: Go to www.scdahlias.org or call 360-659-8687 for more information.
See www.scdahlias.org for tips on planting, dividing and storing dahlias, disbudding, including numerous how-to photos.
Sarah Jackson: 425-339-3037; firstname.lastname@example.org.
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