Family: Compositeae

Origin: Central America (Mexico)

Flower color: nearly all colors are available

Flowering period: July – October

Planting depth to base of bulbs: 2 – 3 inches above the top of the tuber

Spacing between bulbs: depends on the type of dahlia (average is 5-7 tubers per m²)

Type of bulb: tuber

Light requirements: sunny (should include at least a couple of hours morning sun)

Landscape uses: border, and (depending on the type) also in pots and containers. Also as cut flowers from the garden.

Together with gladioli, lilies and begonias, the dahlias are one of the most important and popular summer-flowering “bulbs”. Dahlias are widely cultivated due to their huge range of colors and flower types available, their many uses, and fairly easy cultivation.

Some two hundred years ago, the first Dahlia arrived in Western Europe from its native habitat in Mexico. Nowadays, it is difficult to find this original dahlia among the current dahlia assortment since flower enthusiasts and growers have done much in the way of developing new types, shapes and colors.

Classification

Single-flowered 

Distinguishing characteristics: a central disc with a single outer ring of florets. Height: 16 – 24 inches.

Anemone-flowered 

Distinguishing characteristics: one or more rings of flatter ray florets surrounding tubular florets. Height: 24 – 36 inches.

Collarette 

Distinguishing characteristics: one outer ring of flat ray florets, an inner ring of collar-like florets, and a central group of disc florets. Height: 30 – 48 inches.

Waterlily 

Distinguishing characteristics: fully double inflorescence with flattened shape; florets are flat with margins that curl in slightly. Height: can reach 48 inches.

Decorative 

Distinguishing characteristics: fully double inflorescence with flat florets that are broad and blunt-tipped. Height: 60 inches.

Ball 

Distinguishing characteristics: fully double inflorescence with a ball shape (often flattened) with florets that are blunt or round-tipped. Height: 48 inches.

Pompon 

Distinguishing characteristics: fully double globe shaped inflorescence with involute florets that are blunt or round-tipped. Height: 32 – 48 inches.

Cactus 

Distinguishing characteristics: fully double inflorescence with revolute florets that are narrow and pointed. Height: around 60 inches.

Semi-Cactus 

Distinguishing characteristics: fully double inflorescence with pointed ray florets that are involute for half their length or less. Height: 60 inches.

Peony-flowered 

Distinguishing characteristics: fully double inflorescence with florets that are round ended. Height: 40 inches.

Mignon 

Distinguishing characteristics: small flowers (2 ½ – 4 inches). Very suitable for pots and containers. Height: about 20 inches.

Topmix 

Distinguishing characteristics: small flowers (1 – 3 inches). Very suitable for pots and containers. Height: about 14 inches.

In a pot

Dahlias grown as pot plants are receiving a great deal of interest, and several firms have spent almost ten years hybridizing them. By using new growing methods which are similar to cultivating chrysanthemums in pots, it is now possible to achieve a longer season for top quality pot dahlias.

These developments have led to new series especially created for use as pot plants:

• Dahlianova types: Double-flowered varieties in every color typical of dahlias. They grow no taller than 8 -12 inches. The tubers are denser and smaller than varieties not developed especially for use as pot plants. A few examples: Dahlinova ‘Arizona,’ Dahlinova ‘Ohio,’ Dahlinova ‘Virginia.’
• Gallery series: This series contains cactus and decorative varieties which grow no taller than 12 – 14 inches. A few examples: Gallery ‘Rembrandt,’ Gallery ‘Art Deco,’ Gallery ‘Leonardo.’
• Impression selection: These are collarette dahlias and primarily suitable for bedding and for use on balconies and patios. Depending on the variety, height can range from 12 – 20 inches. Some examples: Impression ‘Festivo,’ Impression ‘Fortuna,’ Impression ‘Fuego.’

Dahlias are not winter hardy and cannot tolerate frost. Many people pot up dahlias indoors 6 weeks prior to planting them outdoors to get a “jump” on the season and thus get earlier blooms. Plant outdoors only after the last spring ground frost. In fall, dig up the tubers and bring them inside before the first fall ground frost. Store the tubers in a cool but frost-free spot until re-planting them next spring. Pinching out the main stems 3 weeks after planting encourages a bushier habit. Taking off the faded blooms during the summer months will prolong the flowering period.

Dahlias are absolutely perfect for borders. Most of them will also excel here along with annual plants because of their extremely long flowering period. The result? A cheerful rainbow of colors. Dahlias can also be assigned a leading role in the perennial border, the tall varieties fitting in perfectly in the back row. While creating a spectacular display when summer-flowering plants are in full bloom, they will still be going strong when the last fall-flowering asters are in bloom. Borders featuring spring-flowering plants simply cannot do without dahlias.

Critics sometimes find dahlias a bit too massive and even too splashy for the border. These remarks, however, are usually aimed at the extremely large-flowered Decorative, Cactus-flowered, and Semi-cactus cultivars. They certainly would not apply to the Peony-flowered varieties such as ‘Bishop of Llandaff’ or its successor ‘Fascination’, nor to the uniquely colored Anemone-flowered or Collerette dahlias. Another dahlia cultivar that fits in beautifully with all kinds of perennial plants, especially blue-flowering ones, is ‘Giraffe’.

When selecting plants for bedding purposes, the color effect they produce is the most important factor. What’s more, plants for bedding must be uniform in size, sturdy, and brightly colored. Finally, they must not grow too tall. When considering all these characteristics, plants from the newly developed Dahlinova, Dahlstar, Gallery and Impression dahlia series would be perfect for bedding purposes. Other dahlias exceptionally suitable for bedding would be the Top-Mix and Mignon dahlias and other naturally low-growing cultivars such as ‘Berliner Kleene’, ‘München’, ‘Red Pygmy’ and ‘Witten’. An advantage offered by the newer varieties, as well as some of the older ones, is their wide variety of colors and their floriferousness. Dahlias from the Gallery Series in particular feature flowers that remain attractive for a longer time on the plant, meaning that less maintenance is necessary to produce a long effective flowering period.

Dahlias are ideal for growing in pots and containers. Especially good for this purpose are the Mignon, Top-Mix, Dahlietta, Dahlstar, Dahlinova, and Gallery dahlias, as well as all other low-growing dahlias with compact habits. Experimenting with somewhat taller dahlias in larger containers or tubs is also recommended. ‘Bishop of Llandaff’, for example, has been grown in containers for years with good results and is showing increasing popularity as a tub plant. The bright colors so typical of dahlias fit in well with other annual plants, but dahlias can also play the leading role by combining them with less conspicuous plants such as Summer cypress (Kochia scoparia), gray-leaved Senecio cineraria or Helichrysum petiolare, or the subtle Polygonum capitatum that can be used at (and tumbling over) the edge of the container.

Provide the pots with proper drainage. Having holes in the bottom and low on the sides, as well as adding a layer of clay granules to the bottom of the pot or container, are musts. Use ordinary potting soil available from any garden center.