Floridata Article

An Addiction to Dahlias: The Easy Way to Fantastic Flowers

Four famous dahlias, showing the great diversity in the blooms. L to R, pink "Otto's Thrill" is a classic Dutch hybrid, obviously hybridized by a man called Otto. Maroon or dark red "Thomas Edison" is one of the all-time famous dinnerplate dahlias with lavish blooms up to 12" across. Introduced in 1907. "Caribbean Fantasy" is a magnificent white, gold and red "explosion" of color. On the far right is "Kogana Fubuki," one of the fantastic Japanese-named hybrids with a stunning multi-petaled flower, white-tipped red petals and golden center.

A gardening expert once said of dahlias, “Never have so many enjoyed so much with so little time and work” And he was right. There’s probably no plant in the flower kingdom that gives the gardener more spectacular reward than the dahlia.

Dahlias are a little like roses. Or hostas. Most gardeners can’t grow just one. Once you grow a dahlia, you want more. And like roses or hostas, there are seemingly endless dahlias to keep a dahlia gardener happy. Growing them is remarkably easy, so that just adds to the frenzy. If you’ve never grown a dahlia, it’s high time you did.


A beautiful bargain. To begin with, dahlias are inexpensive. There are very few flowering plants that cost just a few dollars and give you a big bush-like plant with constant big blooms all summer and fall. Remember, dahlias range from the miniatures, just a few inches tall, to the huge-flowered “Dinnerplates”—the wonderful big glossy-leaved plants that grow up to five feet and bloom with flowers 10 or 12 inches across. Whatever dahlias you choose to plant, the process is the same. And here, we’ll spell it out step by step.

The original dahlia, and the Black Dahlia. The thousands of dahlias we see today are all hybrids from one ragged wildflower that’s native to Mexico. The Dutch hybridizers got their hands on it years ago, and were thrilled at how easily it took to various crosses, changes and “improvements.” Today there are cactus-flowered dahlias, water-lily dahlias, peony-flowered dahlias, daisy dahlias—the parade is endless, and with new color combinations every year. Most of the larger ones, officially called “Decorative (not dinnerplate) Dahlias” are bi-colors or tri-colors, in an ongoing parade of color and form.

But sorry, there is no Black Dahlia. That’s pure Hollywood, the nickname of a famous starlet who was murdered. Look for the Black Dahlia in Hollywood history, not at the garden center.

dahlia tubers
After frosts, it's time to plant. Tubers from last summer are ready to go back into the ground.
planting dahlias
The soil for each hole is worked well, and since these are big dahlias, a stake is put into place early on.
dahlia garden
Our large dahlia garden is planted and fertilized. Now all we need is regular watering and a few weeks. See below.

Tubers, not bulbs. Even though they’re often called “bulbs”, the roots of dahlias are actually “tubers”. (as in “tuberous begonia”) Dahlia tubers look a lot like a bunch of brown carrots, and the stems sprout directly from the tubers—the little budding sprouts that end up as thick strong stems are called “eyes.”

Soil Prep, Food and Fertilizer. Dahlias respond dramatically to feeding. After all, they are making these fat potato-like roots, and the more food they get, the more root mass they’ll make. This not only increases your growth of leaves and flowers, it also increases your tuber clump for an even bigger show the following summer.

So be sure to dig your holes deep and work the soil all around. Enrich the soil with compost or well-rotted manure, and then work in a good 5-10-15 or 5-10-10 fertilizer according to the instructions. With a well-prepared soil bed, your dahlias will create beautiful growth very quickly.

Spacing and planting. Once you have your tubers, it’s important to space them correctly. If you’re planting a big dinnerplate dahlia, it needs room. When grown (and that’s quickly) it’ll be the size of a large rose bush, so plan accordingly. Follow the instructions on your package, but in general, dig the hole in full sun in “good garden soil” near a water source, and place the tuber in with the “bunch of carrots” points down. Simply firm the soil around and over the clump, water well and you’re done.

Staking. If you’re growing big dahlia plants, staking will be important. The beautiful foliage grows on somewhat brittle stems, and often heavy rain, wind or even the weight of the flowers once they’re open can break the plant. You don’t want that to happen, especially when it’s coming into bloom, so set one or two stout stakes beside each tuber after you plant them, and have the twine or “twist-ems” ready to support the stems as they grow. Don’t ignore this instruction. Believe me, it’s worth it. With a little effort, the stakes will be completely hidden by the leaves, but your plant is going to need them.

Disbudding. You’ll read about this in most gardening books, and it applies to two things about dahlias. Some experts suggest removing the first buds which helps the plant into better form. But who can do that and delay your first bloom? It isn’t really necessary.

The second definition refers only to the dinnerplates, and then only if you’re growing for competition in flower shows. It amounts to this: Like many flowers, dahlias set buds with one large one at the tip of a growing stem, and then smaller buds to the left and right of the tip, usually called lateral buds. Disbudding involves removing all but the terminal bud while the buds are small, obviously throwing all the growth into the one remaining bud. It does make that flower bigger that big, but most gardeners aren’t growing their dahlias for flower shows, so most people don’t do it. (See An Unforgettable Flower Show Memory below.)

Pests. Dahlias are surprisingly free of most pests. Most years I’ve grown them, I”ve needed no spray or other insecticide. But they can be a magnet for slugs. Be ready with slug bait, and watch for them. They can do lots of damage in no time.

One year, Japanese beetles from nearby roses discovered my dahlias, and that had to be handled. They can obliterate not only the leaves, but the dahlia flowers, too. So be watchful, and keep the plants pest free.

Cutting Flowers. You simply won’t be able to resist. When you remove flowers for your arrangements, choose whole stems and try to maintain the basic shape of your plant. It will quickly try to replace the branch you remove, and the buds will keep coming—right up until frost.

Saving the tubers in fall. If you grow your dahlias in a hard-frost area, as I’ve done, there will be that morning in late fall when you walk out to your plants and find them pitifully blackened and dead. Remember, the dahlia is really a tropical plant, so when frost hits them, it kills them instantly.

When it happens, here’s all you have to do. It’s really easy: Pull up the plants, chop off the stems a few inches above the tuber, wash off the dirt, and set the tubers in the fall sun to dry. You’ll be amazed that many of your tubers will be two or three times the size they were when you planted them….which means all the more to plant next spring!

One important note: Be sure to LABEL them with color or type, or you’ll have no idea next spring. They all look alike. It always amazes me that such an ugly mass of roots will be giving me such beauty again next spring!

young dahlia plants
About two weeks after planting, the beautiful foliage is up and growing.
dahlia buds
Soon after the foliage appears, buds follow. They're small now, but will soon expand into bloom.
young dahlia plants
By mid-summer, plants are about 2 1/2 feet tall, and first flowers are open. Buds are everywhere!
mature dahlias
A few weeks later, plants are full grown at about 4 feet, and all this color will continue until frost.

Once they’re dry, simply put them in some sawdust or peat moss, and toss them in a big paper bag (no plastic!). Then store them in a cool non-freezing spot in the cellar or garage until next spring. At that time, you may want to divide them, keeping at least 3 eyes per clump, or plant the great big clumps for great big growth.

An Unforgettable Flower Show Memory. Years ago, when I was a young person working in New York City, a friend in my office mentioned that the New York Botanical Garden was having a big show of dahlias in bloom. He had read about it in the newspaper, and was going to see them on his lunch hour. He wondered if I’d like to go.

At this point in my life, gardening was not high on my interest list, and I had never seen a dahlia. But the idea fascinated me, and having never been to the famous NY Botanical Garden, I agreed to go. And I’ve never regretted it.

After a gritty subway ride from Manhattan up to the Bronx where the garden is located, we entered the famous institution through an elaborate entrance. In the distance, I caught sight of the grandiose Victorian greenhouse I’d seen in pictures, and we walked past an incredible pond with gigantic lotus blossoms in bloom - something else I’d never seen.

But around a turn on the pathway, we entered a circular lawn. It must have been about 100 feet in diameter, a perfect circle enclosed in a perfectly trimmed, high curving hedge. And in front of the hedge, dahlias. Each plant was six feet tall or more, staked straight with almost no side branches, and at the top of each, one huge, perfect flower. These gigantic blooms were all at least 12 inches across, and were there in stunning solid colors and rainbows of bi and tri-colors. They were literally explosions of color, each held high and directly facing us as we walked around the circle. Spotlights of beauty. Stunning natural masterpieces, coaxed into perfection by talent and dedication. They were truly breathtaking.

I now appreciate the weeks and weeks of feeding, clipping, disbudding, and staking that went into that show at the New York Botanical Garden. In the years since, I’ve grown a lot of dahlias, but never in that spectacular, formal way. But it is certainly a memory no gardener would never forget.

Dahlia arrangement
Dahlias are always there for fall arrangements, along with the last roses and whatever is left in the garden. (Photo by Don Paulson.)

The Twelve Official Divisions of Dahlias

If you’re the type gardener who likes detail and “official” information, here it is. Like everything else, there are correct names and categories for all dahlia hybrids. The Netherland Flower Bulb Information Center lists the official divisions. The big Dinnerplates are in Division 5, and the trend is toward shorter plants with more and more colorful blooms. (See the latest types at the bottom of the list.)

It’s interesting that the tubers of the 5-foot plants in Division 5 and 8 are not that much bigger than those for the bedding dahlias that grow only about 18” tall. All dahlia roots look about the same; all have the brown, swollen-carrot look. Once they’re out of the ground and the tops are cut off, it’s hard to tell the various types apart.

Division 1. Single-flowering Dahlias. These are some of the oldest types, rarely seen today, and look much like a large daisy or cosmos. Plants grow 16-24” tall.

Division 2: Anemone-flowering Dahlias. These are the beautiful ones with one or more rings of florets, but not really “double.” The central group of petals is tubular. Height: 24 to 48 in.

Division 3: Collarette Dahlias. This group is also daisy-like, but the other ring of petals is flat, while the inner ring is ruffled, creating the “collar.” These are mid-sized dahlias, on mid-size plants, only 30 to 48 in. tall.

Division 4: Water-lily Dahlias. These are some of the most beautiful. Like the name implies, the large flowers resemble the spectacular bloom of a waterlily. Flowers are fully double, but still flattened in shape—really magnificent. Up to 48 in.

Division 5: Decorative Dahlias. These are the big ones. This group includes the “Dinnerplate Dahlias”, while that name is not an official one. Flowers are fully double and the plants are tall. Flower size is the largest, up to 12 inches across. Plants grow up to 60” (5 feet) tall. There is still plenty of work being done on this group of giants. Most of the older hybrids a solid color, with famous names like “Thomas Edison,” (a famous dark red from 1906), Kelvin Floodlight, (the famous pure yellow) and Otto’s Thrill (an unmatched classic pink). Many of the newer ones are bi-colored or tri-colored with names like Caribbean Fantasy and Explosion. There also new ones being hybridized by the Japanese, with names like “Kogana Fubuki.”

Division 6: Ball Dahlias. The flowers for these are rounded, like a ball. They resemble some larger double zinnias, but with the richer dahlia colors and texture. Loaded with petals, these flowers are mid-sized on plants to 48 in.

Division 7: Pom Pom Dahlias. These popular dahlias are also ball-shaped, usually perfectly round. They have smaller flowers than the “Ball Dahlias”. 32-48 in. tall.

Division 8: Cactus Dahlias. These are unique, and carry blooms very similar to cactus flowers. That means they’re fully double, and have tubular petals that are pointed, giving a starburst appearance. This group includes some spectacular color combinations. Big plants, to 60 in. tall.

Division 9: Semi-Cactus Dahlias. This group is similar to the above, but the petals are not completely “Involute” (tubular) and pointed.

Division 10: Peony-flowering Dahlias. The name says it all. These dahlias imitate the fully double, fluffy look of a peony. 35” plants.

Division 11: Mignon Dahlias. These are the small “bedding dahlias” with single or semi-double daisy flowers in strking colors. They are often sold in 6-packs with other annuals in the spring. Flowers are only 3-4 in. wide, and plants are only about 28” tall or less, making them great for planters, patio pots and window-boxes.

Division 12: Topmix Dahlias. More small bedding dahlias like the Mignons above. Roughly the same size, perhaps a bit smaller. These small bedding plants are more popular every year.

The Latest in Dahlias: The Dahlianovas, the Gallery Series, and the Impression Dahlias. Recent hybridizing has resulted in all sorts of shorter dahlias with many of the glamorous qualities of the older, taller ones. The Dahlianova Dahlias have double flowers like the giants, but grow only 8-15 in. tall. The Gallery Series is mid-sized, 12–14 in. with double, often bi-colored flowers that echo the colors of famous painters. For example, there are Gallery Dahlias named “Rembrandt” and “Leonardo.” The Impression Series is a little larger, growing to 12-20 inches, and the flowers are of the classic “collarette” type in very hot new color combinations. The Dutch hybridizers, who have learned a lot about marketing over the years, have named this group with a Spanish flair, and for some reason, all the names begin with “F”. Examples are “Impression Fuego”, Impression “Festivo”, and Impression “Futuro”.

Ray Allen 12/2/07 - used by permission

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