Family: Compositeae

Origin: Central America (Mexico)

Flower colour: nearly all colours are available

Flowering period: July – October

Planting depth to base of bulbs: 5 – 7 cm above the top of the tuber

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

Type of bulb: tuberous root

Light requirements: sunny (at least for a couple of hours AM 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 the huge range of colours and flower types available, its 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 as flower enthusiasts and growers have done much in the way of developing new types, shapes and colours.

Classification

Single-flowering 

Distinguishing characteristics: one ring of florets, central group of disc florets. he height is 40 – 60 cm.

Anemone-flowering 

Distinguishing characteristics: one or more rings of florets, central group of tubular florets. The height is 60 – 90 cm.

Colarette 

Distinguishing characteristics: one outer ring of flat florets and an inner ring of collar florets, central group of disc florets. The height is 75 – 120 cm.

Water-lily 

Distinguishing characteristics: fully double, flattened shape, florets are flat with slightly curved margins. The height can be 120 cm.

Decorative 

Distinguishing characteristics: fully double, flat florets are broad and blunt-ended. The height 150 cm.

Ball 

Distinguishing characteristics: fully double, ball shaped (often flat), florets are blunt or round ended. The height 120 cm.

Pompon 

Distinguishing characteristics: fully double, globe shaped, involute florets are blunt or round ended. The height is 80 – 120 cm.

Cactus 

Distinguishing characteristics: fully double, involute florets are narrow and pointed. The height is about 150 cm.

Semi-Cactus 

Distinguishing characteristics: fully double, pointed florets are involute for half their length or less. The height 150 cm.

Peony-flowering 

Distinguishing characteristics: fully double, florets are round ended. The height is 100 cm.

Mignon 

Distinguishing characteristics: small flowers (6 – 10 cm). Very suitable for pots and containers. The height is about 50 cm.

Topmix 

Distinguishing characteristics: small flowers (3 – 5 cm). Very suitable for pots and containers. The height is about 35 cm.

In a pot

Dahlias grown as potted plants are receiving a great deal of interest, and several firms have spent almost ten years hybridising 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 potted dahlias.

Three new groups can be distinguished:

• Dahlianova types: Double flowering varieties in every available color. They become no taller than 8 -12 inches (20-30 cm). The tubers are denser and smaller than those in the normal assortment. A few examples: Dahlinova ‘Arizona,’ Dahlinova ‘Ohio,’ Dahlinova’Virginia.’
• Gallery series: This series contains cactus and decorative varieties which become no taller than 12 – 14 inches (30-35 cm). A few examples: Gallery ‘Rembrandt,’ Gallery ‘Art Deco,’ Gallery ‘Leonardo.’
• Impression selection: These are colarette dahlias and primarily suitable for bedding and for use on balconies and patios. Depending on the variety, height can range from 12 – 20 inches (30 to 50 cm). 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. Only plant outdoors after the last spring night frost. In fall, dig up and bring tubers inside before the first fall night frost. When you store the tubers in a cool but frost-free spot you can keep them until re-planting time next spring. You can increase the bushiness of the plant by pinching out the tips of the main stems 3 weeks after planting. Taking off the faded blooms during the summer months will prolong the flowering life.

Dahlias are absolutely perfect for borders. Here, often combined with annual plants, most of them also excel due to their extremely long flowering period. The result? A cheerful rainbow of colours. Dahlias can also be assigned a leading role in the perennial border, the tall varieties fitting in perfectly in the back row. While making their presence known when the summer-flowering plants are in full bloom, they are still going strong with the last autumn-flowering asters are in bloom. Borders featuring spring-flowering plants simply cannot do without dahlias.

Critics sometimes find dahlias a bit too massive, and sometimes they are even said to be too splashy for the border. These remarks, however, are usually aimed at the extremely large-flowering Decorative, Cactus-flowered, and Semi-cactus cultivars. They certainly do not apply to the Peony-flowered varieties such as ‘Bishop of Llandaff’ or its successor ‘Fascination’, nor to the uniquely coloured 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 colour effect they produce is the most important factor. What’s more, plants for bedding must be uniform in size, sturdy, and brightly coloured. 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 colours 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 an effective, long 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 colours so typical of dahlias fit in well with other annual plants, but one can also choose to let dahlias play the leading role by combining them with less conspicuous plants such as Summer cypress (Kochia scoparia), grey-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 proper drainage for the pots. 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 centre.