How To Grow Dahlias
All of your dahlia questions answered in one place! Find planting instructions, staking advice, tips for end-of-season 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 - 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 gardener happy. If you've never grown a Dahlia, it's high time you did.
When & Where To Grow Dahlias
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.
Starting Dahlias Indoors
For most gardeners, we recommend giving plants a head start in containers while soil warms up outside - reaching at least 60 degrees F. Generally, you'll plant dahlias outside around the same time you plant tomatoes.
If that’s not until late May or early June where you live, you can start dahlias indoors, 4-6 weeks before your last frost date. In containers, lay tubers on their sides with the stems up and cover with 2 inches of soil. Wait until you see new growth breaking through to water.
If you want to leave plants in the containers, choose more compact vareities before planting, and look for a 12-16 inch diameter container to plant the tubers.
How To Plant Dahlias Outdoors
1. Choose a location with good light. Dahlias require full sun, with 6 or more hours of sunlight daily. Less sun will result in decreased flowering.
2. Prepare your soil. Dahlias prefer rich and well-drained soil, and they're great for sandy, loamy, or acidic soil. Enrich the soil with compost or well-rotted manure, and then work in a good organic fertilizer according to the instructions. Dig several inches deeper than the required depth, to loosen the soil before planting and help with drainage. With a well-prepared soil bed, your Dahlias will create beautiful growth very quickly.
3. Dig holes at the proper depth and spacing. Follow the depths listed on your package - this will vary based on your varieties, with larger Dahlias spaced approximately one tuber per square foot. The largest varities of Dinner Plate Dahlias will do best with spacing 12-18 inches apart to allow for foliage and flowers to grow. Compact varieties can be planted with mulitiple tubers per square foot.
4. For larger varieties, generally those growing 3 feet or taller, we recommend staking when you plant. Read on for our tips on Staking Dahlias!
If you're growing big dahlia plants, staking will be important. We recommend being pro-active, and setting up your stakes when you plant your Dahlia tubers. The beautiful foliage grows on somewhat brittle stems, and 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!
Set one or two stout stakes beside each tuber after you plant them. Wooden stakes can be buried or hammered in. Metal stakes can be placed in the soil more easily and are a great option if you find that your Dahlias need a little extra support after they've grown in.
Have the twine or 'twist-ems' ready to support the stems as they grow. With a little effort, the stakes will be completely hidden by the leaves, but you will thank yourself when your big, beautiful flowers a growing with support.
Growing & Care For Dahlias Throughout The Season
Growth Habit: Dahlias grow quickly, producing bush plants and flowering in the first season.
Watering: Water regularly, and try to keep your foliage dry. Avoid overwatering, as soggy soil can lead to rotting tubers. We recommend less frequent, but deep watering.
Fertilizing: Dahlias respond dramatically to feeding. After all, they are making large 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.
Mulching: In very hot, dry areas, you may want to mulch to help retain moisture, but in most areas, we recommend skipping mulch so that the soil can stay warmer and foliage can stay dry.
Pests & Diseases: 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.
If you find your Dahlia leaves chewed, it's most likely from caterpillars. We recommend looking leaves over and picking them off if you find them. If you find powdery mildew, we recommend Serenade, and avoiding too much watering on leaves - it may also help to spread out or thin your planting to prevent the spread of powdery mildew. Stem rot may occur in poorly draining or overly wet soil.
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.
Cutting Dahlia Flowers
You simply won't be able to resist - you only need a few flowers for a beautiful bouquet! 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. Deadheading spent flowers will encourage more flowers to bud.
Disbudding or Pinching Back Dahlias
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 of disbudding refers only to the Dinner Plate Dahlias, and then only if you are growing for competition in flower shows. It amounts to this: Like many flowers, dahlias set one large buds 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.
Another techinque, pinching dahlias, applies the reverse. If you trim off the central terminal bud, it will encourage more growth from the lateral buds, giving you many flowers perfect for cutting. As you grow and experiment, you will find the technqiue that works best for you!
Dahlia Collections For Beautiful Bouquets
End Of Season Dahlia Care and Tuber Storage
Dahlias will sometimes overwinter in the garden in zones 8 and higher, but they intensely dislike wet feet, and are prone to rot. It’s better to lift and store during the cool season, giving Dahlia tubers a winter hibernation period somewhere cool, dark, and dry.
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.
After 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!
Once they're dry, simply put them in some sawdust or peat moss, and toss them in a big paper bag (no plastic - this will encourage rot). 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.
One important note: Be sure to LABEL your Dahlia tubers with color or type, or you'll have no idea what's what next spring. They all look alike. It always amazes me that a mass of roots will be giving me such beauty again next spring!
- For more detail on storing dahlia tubers, Learn More: How To Dig and Store Dahlias For The Season
Watch: All About Dahlias
The 12 Official Divisions of Dahlias
The thousands of dahlias we see today are all hybrids from one ragged wildflower that's native to Mexico. 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 — the parade is endless, with new color combinations introduced every year. Most of the larger ones, officially called "Decorative" Dahlias, are bi-colors or tri-colors, adding to the list of options for color and form. 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:
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" tall
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.
Height: 16-24" tall
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!).
Height: 32-48" 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.
Height: up to 60" 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.
Height: up to 60" 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, with petals that are more broad and rounded .
Height: up to 48" tall
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.
Height: 30 - 48" tall
Peony Flowering Dahlias
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.
Height: 35" tall
These are the small 'bedding dahlias' with single or semi-double daisy flowers in striking colors. Flowers are only 3-4" wide on compact plants, making them great for planters, patio pots and window-boxes.
Height: up to 28" tall
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.
Height: up to 28" tall