With their intense color, vigor, and ability to keep flowering until the first frosts, dahlias are invaluable for bringing life to your garden. Dahlias like well-balanced & composted soil, and full sun. Dahlias are generally winter hardy in zones 7-10 (except for isolated areas that may get below freezing) and can stay in the ground. In these marginal areas or colder zones, dahlia tubers should be dug up and stored over winter.

Frances Palmer’s garden in September, filled with dahlias at the peak of bloom. Photo by: Frances Palmer.

Zones:

Generally winter hardy in zones 7-10. In colder zones, tubers can be dug up and stored for winter and re-planted in Spring, 1-2 weeks before last frost.

Height/Spread:

1-6 feet/1-3 feet

Exposure:

Full sun

Soil:

Well-balanced, organically rich

Water:

Medium

Color:

Varieties include red, pink, lavender, purple, orange, yellow, and white

Bloom Time:

July to September

Dahlia types:

With 42 species and thousands of cultivars, dahlias offer plenty of variety. Differences in color, flower form, size and foliage make it easy to find a dahlia you'll love. Learn more about the types of dahlias.

Tomato cages and wooden stakes can be used to support dahlias. Photo by: Frances Palmer.

According to Frances Palmer, well-known potter and dahlia enthusiast, May is a good time to plant dahlia tubers. Here are instructions for planting:

  1. Place growing cages (tomato cages work well) in the soil and drive in 2-3 stakes adjacent to them for support.
  2. Dig the hole:
    For new or single tubers:
    Place them in a fairly shallow hole, approx. 3 inches deep, with the new bud facing up. Gently cover with dirt.
    For larger groups of tubers:
    Place in a deeper hole, keeping them approx. 3 inches below the surface.
  3. Attach a label to the cage for identification.
  4. Do not water, as there should be enough moisture in the soil this time of year. Over-watering causes tubers to rot.
  5. The first leaves should poke through the surface in about 1-2 weeks.

Starting dahlias indoors:

If you live in a cold climate and want to get a head start, dahlia tubers can be started inside 6 weeks before moving them out to the garden. Plant them in pots with potting soil or sand and provide plenty of light and water. When the ground temperature in your garden reaches 60°F it is safe to transplant your dahlias.

Planting dahlias in containers:

Low-growing or dwarf dahlias are best for growing in containers. Use a pot with drainage holes and a good quality potting mix. When starting, barely cover the tuber with soil, more can be added as the plant’s stem grows.

Dahlia tubers can be stored for the winter in your basement or garage. Photo by: Frances Palmer.

Pinching:

When the first set of leaves is about 8-12 inches high, pinch out the center bud to encourage multiple stems to grow and produce more flowers. Sometimes this process is called topping.

Fertilizing:

Bone meal or a mixture of 2 parts bone meal to 1 part sulfate of potash can be applied 2-3 times between June-October to encourage blooming. If your soil is healthy, this may not be needed at all.

Staking:

As your dahlias grow, gently encourage the stems to stay inside the cage for support. Garden twine can be tied around the outside for additional support.

Disbudding:

If you want dahlias with longer, stronger stems and bigger flowers then you’ll need to remove the two pea-sized buds flanking the central bud. For certain types of dahlias, it may be beneficial to remove more buds further down the plant. See this disbudding explanation from the Snhomish County Dahlia Society.

Deadheading:

Deadheading dahlias will keep your plants looking tidy and encourage them to continue blooming. Many gardeners report that when they diligently deadhead their dahlias, they will bloom until the first frost. Be careful not to remove new buds, which are rounded—the spent flowers have a triangular or cone shape. Make your cut slightly higher than where the stem of the flower meets a main branch. With the spent flower removed, new buds will develop at this intersection and you’ll have more flowers in a few weeks.

Digging and storing tubers:

If you live in an area that will require you to store your dahlia tubers over winter, here are some helpful instructions:

  1. After the first frost, flowers & stems will immediately wilt. Leave them in the ground for a week or 2 after a few more strong frosts have occurred.
  2. Pull out support cages and/or stakes.
  3. Dig outside the circumference of the tubers with a pitchfork. The larger the plant, the larger the tuber; but don’t worry - if tubers are broken apart or damaged during digging, this will not damage the plant.
  4. Cut off dead stems 2-3 inches above the tuber bunch to give yourself something to hold onto, and gently shake off as much dirt as possible.
  5. Place a tag on the cut stem for identification.
  6. Place a few inches of peat moss or wood shavings in the bottom of a large cardboard box.
  7. Give the tubers a final shake to remove any further dried dirt, and layer them in the box with larger tubers on the bottom. At about half-way full, add another layer of packing material and more tubers. Cover completely with the storage material, shake to settle and top off with more storage material. Fold flaps to close.
  8. Store in a cool basement or garage that gets to about 40 degrees, but not below freezing.

DESIGN WITH DAHLIAS

The lower stems of dahlias tend to be unattractive and the plants have a heavy quality, so that without staking, they tend to flop. Distributing them amongst other plants helps support their weight and hides their lower stems. The taller varieties will grow well with perennials and ornamental grasses toward the rear or center of borders, while the shorter ones mix well with annuals or shorter perennials. The smallest make good container plants.

Magenta ‘Ambition’ and deep-red ‘Nuit d’Eté’ dominate this late-season border; blue Aster x frikartii ‘Mönch’ and gladioli play supporting roles. These late bloomers pick up where summer-flowering plants leave off, giving the garden a grand sendoff for winter. Photo by: Marianne Majerus.

Dahlia flowers inject strong color into a planting, so when choosing them it helps to think about what other flower or foliage colors there are going to be, as the dahlias will pick these up and echo them loudly. Other late-flowering perennials are always a good match, particularly if colors relate but form and texture are different, as with yellow dahlias and fluffy goldenrods, or purple-toned dahlias and asters in purple-blue shades. They can also look surprisingly good with grasses as the contrast is total—big solid exuberant flowers against finely textured shapes and colors too subtle to offer any competition. In more formal settings, their strong colors can be wonderfully enhanced by the cool foliage of clipped hedges.

By September, dahlias will be in their full glory. Good cutting dahlias tend to be the larger varieties because of their longer stems. If you cut for use in vases after they open, dahlias will continue to bloom until first frost.

However they are used, dahlias help the garden end the year on a high note.

DAHLIA PICTURES

Swipe to view slides

Photo by: Andrea Jones.

‘SASSAFRASS’

Height: 4 feet

Flower form: Laciniated, Cactus

Bright-gold, 6-inch-wide blossoms with deeply cut petals, ‘Sassafrass’ was introduced in 2010, derived from ‘Cheyenne’, which has streaks of pinkish-red.

Photo by: Andrea Jones.

'GIGGLES'

Height: 3-4 feet

Flower form: Collarette

Three-inch plus flowers are light orange with a very pronounced and faintly purple-flushed collar—an unusual and striking combination. Noted as a particularly prolific bloomer.

Photo by: Andrea Jones.

'BEE HAPPY’'

Height: 3 feet

Flower form: Collarette

This 4-inch-wide flower is bright pink with burgundy tones towards the center. The color is wonderfully complemented by the almost- lack leaves and stems, making it a compelling garden plant or even one for a larger container.

Photo by: Andrea Jones.

'GINGER SNAP'

Height: 4 feet

Flower form: Waterlily

The beauty of this variety is the way it gently fades from gold-yellow in the center to a light peach around the edges. Producing relatively small flowers from side branches on a compact plant, it’s good for cutting.

Photo by: Andrea Jones.

'SMARTY PANTS'

Height: 3 feet

Flower form: Decorative

The rich coral of this variety reflects the contemporary interest in combining dark foliage with strongly colored flowers. Tends to bloom early and form bushy plants. Its long flower stems make it good for cutting.

Photo by: Andrea Jones.

'LUCKY DUCKY'

Height: 4 feet

Flower form: Anemone

Three-inch-wide flowers in a uniform soft yellow with a prominent pincushion center; the surrounding ray petals tend to bend back as the flower ages. The plant grows with a distinctly upright habit.

Photo by: Andrea Jones.

'TINY TREASURE'

Height: 3-4 feet

Flower form: Pompon

A virtually pure-white variety. The inch- to inch-and-a-half-wide flowers have strong but rather short stems for cutting; however, the plant’s compact habit and relatively low height make it a good border plant.

Photo by: Andrea Jones.

'TUTTI FRUTTI'

Height: 4 feet

Flower form: Cactus

This variety has 5-inch fuchsia flowers and distinctly quilled petals. Blooms are produced on lateral shoots (side shoots), which means that there are plenty for cutting.

Photo by: Andrea Jones.

'CRAZY LEGS'

Height: 4 feet

Flower form: Stellar

The 3-inch-wide flowers are distinguished by the red reverse to the bronze petals. It is noted as a prolific bloomer with strong stems on a plant with handsome foliage.

Photo by: Andrea Jones.

'LAUREN MICHELLE'

Height: 4 feet

Flower form: Waterlily

Three-inch-wide lavender flowers with a darker center and reverse to the petals. Flowers are plentifully produced at a 45-degree angle from the plants. They last especially well in the vase.

WHERE TO BUY DAHLIAS

Frances Palmer’s recommendations for ordering dahlia tubers:
Endless Summer Flower Farm
Fern Cliff Gardens
Old House Gardens
Dahlias.com

RELATED:
Summer Arrangements: Sunflowers, Zinnias, and Dahlias
Summer Flowering Plants

Free Weekly NewsletterSign up for weekly gardening inspiration and design tips

Join thousands of design-conscious readers for exclusive offers, gardening inspiration and innovative design solutions for enjoying outdoor spaces.

* Required Fields
We will never sell or distribute your email to any other parties or organizations.

More about the newsletter

Come on a journey with us! Explore amazing gardens, view beautiful plants, and gain insights from the world’s best designers. Click on the issue to preview its contents.

Autumn 2017 - Issue 200Autumn 2017 - Issue 200
Follow Us Garden Design Magazine Facebook Garden Design Magazine Twitter Garden Design Magazine Google Plus Garden Design Magazine Pinterest Garden Design Magazine Instagram Garden Design Magazine Youtube

Not Ready to Commit to a Subscription?

Try an issue of Garden Design magazine for free (we know you’ll love it)! Just pay $4.95 for shipping and handling.

With our free single-issue trial order, we will send you a copy of the Autumn 2015 issue of Garden Design. Offer only available in the United States, and one per household.

Get your free issue!