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Finally, all of your dahlia growing questions answered in one place! Scroll down to find planting instructions, staking advice, end-of-season care, proper tuber storage, and more. Or, watch our easy-to-follow dahlia planting video.
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 a more spectacular reward than the dahlia.
Dahlias are a little like roses, or hostas, or even tomatoes. Most gardeners can't grow just one. Once you grow a Dahlia, you want more. And like roses, hostas, and tomatoes, there are seemingly endless dahlias to keep a Dahlia gardener happy. Growing them is remarkably easy, which only adds to the frenzy. If you've never grown a Dahlia, it's high time you did.
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 organic fertilizer according to the instructions. With a well-prepared soil bed, your Dahlias will create beautiful growth very quickly.
Once you have your tubers, it's important to space them correctly. If you're planting a big Dinnerplate Dahlia, it will need 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 arranging the 'bunch of carrots' with the points facing down. Simply firm the soil around and over the clump, water well, and you're done.
If you're growing big dahlia plants, staking will be important. The beautiful foliage grows on somewhat brittle stems, and oftentimes heavy rain, wind or even the weight of the flowers once they've opened can break the plant. You don't want that to happen, especially at bloom time, 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.
Stakes can be placed at planting time.
Or, stakes can be placed after plants have grown in.
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 take on a better form. But who can do that and delay the first bloom? It isn't really necessary.
The second definition refers only to the dinnerplates, and then only if you are 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 (the terminal bud), 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, effectively throwing all of the plant's growth energy into the one remaining bud. While this practice can make a single flower bigger than big, most gardeners aren't growing their dahlias for flower shows, so most people don't do it. (See An Unforgettable Flower Show Memory below.)
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.
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. Slugs 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 by occasionally flicking any Japanese beetles into a container of soapy water.
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 this 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 what's what 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!
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 leave them whole for planting the great big clumps for great big growth.
Want more detail on storing dahlia roots? We have written a detailed blog about digging and storing dahlias, or you can find some excellent info recommended by OldHouseGardens.com at the Colorado Dahlia Society's excellent website.
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.
Dahlias are generally classified by the diameter of their blooms, but also by the growth style of their petals and the overall shape of their flower heads. Here are all of the Dahlias you're likely to come across:
Whichever Dahlias you choose to plant, the process is the same. Below, we'll spell it out for you, step by step!
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, with new color combinations introduced every year. Most of the larger ones, officially called "Decorative" (not dinnerplate) Dahlias, are bi-colors or tri-colors, adding to the list of options for color and form. (See the complete list of the Twelve Official Classifications of Dahlias at the bottom of this article.)
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.
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.
These are some of the oldest types, rarely seen today, and look much like a large daisy or cosmos. Simple, sweet, and charming. Difficult to find at retail nurseries and big box stores. Plants grow 16-24' tall.
These are the beautiful single flowers with one or more rings of florets, but not really 'double.' Resemble Anemone, the famed Greek 'wind flower'. The central group of petals is tubular. Height: 24 to 48 in.
This group includes the big ones, such as the "Dinnerplate Dahlias'. 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.
The flowers for these are rounded, like a ball. They resemble some larger double zinnias, but with richer colors. Loaded with petals, these flowers are mid-sized on plants to 48 in.
These popular dahlias are also ball-shaped, usually perfectly round. They have smaller flowers than the 'Ball Dahlias' and look charming in a vase or handheld bouquet (popular with brides!). 32-48 in. tall.
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.
This group is similar to the Cactus Dahlias, but the petals are not completely 'Involute' (tubular) and pointed. They have a less spiky and slightly softer appearance. Great at maintaining their shape throughout harsh weather.
The name says it all. These dahlias imitate the fully double, fluffy look of a classic peony, making them a great choice for growing within a shorter time frame. 35' plants.
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.
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. Up to 48 in.
These are the small 'bedding dahlias' with single or semi-double daisy flowers in striking colors. Flowers are only 3-4 in. wide, and plants top out at 28", making them great for planters, patio pots and window-boxes.
More small bedding dahlias like the Mignons above. Roughly the same size, perhaps a bit smaller. These small bedding plants are also perfect for containers, and will produce abundant blooms.
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 to15 in. tall. The Gallery Series is mid-sized, 12 to 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'.
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.
What are you waiting for? Now you know all you need to know to grow beautiful dahlias. Each year, we offer the tubers on advance sale for spring which begins in December. If you order then, you'll save a bundle, and your tubers will arrive at the proper planting time for your area. Enjoy!