Dahlia: planting, maintenance and growing tips

Botany and description

Originating from the high plateaus of Mexico and Central America, the Dahlia belongs to the large family of Asteraceae, which includes daisies, asters, and echinaceas. There are 30 species and nearly tens of thousands of cultivars: today, nearly 20,000 horticultural varieties are found all over the world. Most are derived from Dahlia pinnata and D. coccinea. Discovered in the 16th century, the Dahlia was only introduced to Europe two centuries later. The Dahlia imperialis, the botanical species that bore simple flowers, was then very different from the modern Dahlia.

From its origins in the dry Mexican environments, it has retained its fondness for warmth and sunlight but has a congenital sensitivity to cold! Moderately hardy, the Dahlia is very sensitive to cold, it is obligatory to winter its tubers in most of our regions as it fears frost. It cannot withstand temperatures that drop persistently and often below -5°C. However, if stored all winter well protected from frost, it will bloom again for many years.

Today, the Dahlia has become popular throughout France, found in all summer flower beds. There are two main types: large-flowered tuberous Dahlias and dwarf Dahlias for easy reproduction by sowing. Among the most appreciated and widespread are the Dahlias with anemone flowers, with orchid flowers, collarette Dahlias, decorative Dahlias, pompon and ball Dahlias, cactus and semi-cactus Dahlias, giant Dahlias, and dwarf Dahlias, both simple and double.

The shape of Dahlia flowers varies according to the varieties: ball, water lily or cactus flower…

The Dahlia is part of a vast family with very varied shapes, colours, and heights. The tallest specimens easily reach 1.50 m, and even more in fertile soil, with a spread of 45 to 80 cm. Among them is Dahlia Imperialis, the botanical ancestor of garden Dahlias, which can reach up to 3 m in height. Intermediate Dahlias grow between 80 cm and 1.10 m. Dwarf varieties, ranging from 0.25 to 0.70 cm, do not require staking.

This perennial has swollen, tuberous roots, gathered in bundles, resembling small potatoes. Edible, they were initially cultivated for consumption. However, its rather tasteless roots were soon neglected in favour of the plant’s exceptional flowering.

From its bushy and upright stump emerge rigid, tubular, erect, hollow, and ramified stems bearing inflorescences from July to October (until November in temperate climates) that renew themselves throughout the summer without interruption.

The Dahlia flower has a strong character, a personality so pronounced that it stands out among thousands. Its solitary head inflorescences are formed of one or more rows of radiating ligules that surround, depending on the variety, a central disc of more or less apparent pistils. The diameter of the flowers ranges from 10 cm to 25 cm or even more! They are classified according to the size of their inflorescences:

• Giant: more than 25 cm in diameter (Giant Dahlias)
• Large: from 20 to 25 cm in diameter (Cactus Dahlias, Ball Dahlias)
• Medium: from 15 to 25 cm in diameter (Water Lily Dahlias)
• Small: from 10 to 15 cm in diameter (Anemone Dahlias, Collarette Dahlias, Decorative Dahlias)
• Miniatures: less than 10 cm in diameter (Pompon Dahlias)

[caption id="attachment_13776" align="alignnone" width="1172"] Giant Dahlia ‘Emory Paul’-‘Mel’s Orange Marmalade’-‘Burlesca'[/caption>

Giant Dahlias, such as Dahlia ‘Emory Paul’, bear enormous flowers that can reach up to 35 cm in diameter, the size of a plate.

Another variable of the Dahlia is the shape of its flower, which establishes a classification. These ligulate, non-fragrant flowers can be simple, semi-double, or very double. The shape of the ligules varies according to the cultivars: curled, flat, lace-like…

The Decorative Dahlias do not have a central disc but large, double flowers with generally flat petals, rounded at the tip and slightly curved, sometimes resembling a water lily or a camellia . The elegant semi-cactus or Cactus Dahlias bear long, curled, pointed petals that form a pom-pom heart resembling a cactus flower, as seen in Dahlia Mel’s Orange Marmalade. In this group, the narrow, very elongated ligules of the head curl over more than half their length. The lace cactus is characterized by large, cut flowers with pointed, flat, or curled petals ending in forked tips, reminiscent of lace.

Others, formed by a crown of wider ligules surrounding a very double heart of smaller florets, an anemone. Some Dahlias have long, incurved or turned ligules, arranged in a star shape reminiscent of an orchid.

The collarette Dahlias or simple flowers only have a single crown of petals around a central disc surrounded by an inner collar of shorter ligules (the heart and tips often offer a surprising contrast, as seen in Dahlias ‘Pooh’ or ‘Fashion Monger‘).

Imbued with fantasy, the Honka Dahlias bear star-shaped flowers, with fine, very curled petals detached from one another around an orange centre, making them resemble delicate windmills or curious spiders.

In contrast, we find the pompon Dahlias, very graphic, whose tubular ligules form a spherical inflorescence of about 10 cm for the largest, sometimes flattened at the top, presenting an alveolate structure, similar to a beehive, as seen in Dahlia ‘Burlesca’. The ball Dahlias or spheres bear flowers similar to pompon Dahlias, but larger, with a diameter that can reach 12 cm.

The flowering of the Dahlia is of incredible colour richness: its flowers come in an infinite palette of colours ranging from light pink to lilac pink, from wine to crimson red, from apricot to carmine salmon, from pure white to café au lait or primrose yellow, from indigo violet to lilac blue (‘Worton Blue Streak’ is currently the bluest cactus!).

Very good for vase arrangements, Dahlia heads make wonderful summer bouquets rich in colour. Some varieties, such as Dahlia ‘Karma Lagoon’, have been specially developed for cut flowers.

Deciduous, the abundant foliage adds a certain lushness and highlights the exotic colours and voluptuous shapes of the flowers. The opposite leaves, finely dentate, 20 to 50 cm long, are either pinnate or very rounded and divide into three to five leaflets, more or less leathery. The colour of the foliage also allows for beautiful variations, ranging from light green to emerald green or bronze green or even purplish (Decorative Dahlia ‘Purple Flame’, Happy Single ‘Juliet’, Dahlia Happy Single ‘Flame’) depending on the different types.

[caption id="attachment_13851" align="alignnone" width="1172"] Dahlia ‘Pooh’ – ‘Happy Single Juliet’ – Honka ‘Pink’- ‘Fashion Monger’

Contrary to popular belief, the Dahlia is not difficult to cultivate, but it does require some attention. It will only be happy and floriferous in a warm and sunny situation. While it adapts to all soils, it thrives in fertile soil, rich in humus, fresh, and well-drained, preferably neutral, neither acidic nor calcareous. It likes light soils that remain fresh and kept sufficiently moist with good mulch during the growing season. The Dahlia does not tolerate standing water, especially in spring and autumn. A cool soil allows it to develop vigorously. It requires, to bloom well, a soil rich in organic matter. It will never be lush and will struggle in poor, sandy soil. Large Dahlias are quite susceptible to wind or heavy rain. If you want to avoid unsightly staking, it is better to give them a place sheltered from prevailing winds that could cause the stems to bend.

Dahlia ‘Ridel’ and Hordeum jubatum (mane barley) – credit-Noun – MAP[/caption>

An essential in church gardens, the Dahlia is a versatile flower that brings colour, relief, and originality to flower beds, rockeries, borders, and flowering pots as well as to the vegetable garden. The Dahlia can be grown alone, but is preferably planted in groups, in the middle or background of a sunny bed, associated with grasses and other vigorous perennials that will act as supports, preventing their flowering stems from lying down unsightly. Dwarf varieties are reserved for borders or planters. Magnificent in beds, decorative Dahlias will make excellent cut flowers for bright and colourful summer bouquets.

This plant was named “dahlia” in honour of the Swedish botanist Andreas Dahl.

Main species and varieties

Les Dahlias à fleurs d’anémone

Les Dahlias cactus et semi-cactus

Les Dahlias collerette

Les Dahlias décoratifs

Les Dahlias géants

Les Dahlias nains simples et doubles

Les Dahlias pompons et balles

Ils se caractérisent par de grandes fleurs formées d’une couronne de pétales aplatis entourant un cœur très double de fleurons plus petits. Leurs coloris inédits, parfois contrastés, attirent inévitablement tous les regards. On y retrouve des sujets de belle stature à intégrer dans les massifs de vivaces comme des variétés naines, idéales en pot ou encore pour composer de jolis bouquets d’été.

Dahlia Blue Bayou

its frizzy red heart contrasts with a lilac-coloured crown. Ideal for rockeries, borders and planters.

• Flowering time August to November
• Height at maturity 1 m

See the product sheet

Dahlia Anemone Soulman

We love its enchanting garnet red colour.

• Flowering time August to November
• Height at maturity 70 cm

See the product sheet

Il s’agit d’une catégorie horticole définie par la forme de la fleur qui… ressemble à une fleur de cactus ! Ils portent de très grandes fleurs doubles de 12 à 20 cm à l’aspect joliment ébouriffé et aux pétales effilés et pointus complètement enroulés. Les semi-cactus présentent des fleurs semblables mais à ligules moins larges et moins longuement partiellement enroulées. Les plus hauts offriront un point de mire surprenant en fond de massif. Les dahlias cactus nains, ne dépassant pas 60 cm de haut, seront parfaits en bordure ou premier plan de massif.

Dahlia Urchin

Its frizzy deep raspberry flowers catch the eye and are magnificent in bouquets.

• Flowering time August to November
• Height at maturity 1 m

See the product sheet

Dahlia Blue Record

Its flowers are a replica of those of the taller varieties, with a smaller diameter (10 cm).

• Flowering time August to November
• Height at maturity 60 cm

See the product sheet

Dans ce groupe les fleurs sont simples parées d’un cœur ébouriffé et contrasté. Les ligules larges et plats du capitule sont disposées régulièrement en couronne autour d’une collerette de petits pétales courts qui dévoilent un cœur jaune. La collerette, souvent d’une couleur différente, offre un contraste surprenant. Les variétés naines, ne dépassant pas 40 cm de hauteur, sont tout simplement sensationnelles en bordure fleuries et en pots.

Dahlia 'Pooh'

Contrasting effect for this Dahlia with large yellow flowers and a red and yellow collar.

• Flowering time August to December
• Height at maturity 1,20 m

See the product sheet

Dahlia 'Impression Fantastico'

A particularly elegant dwarf dahlia with mahogany petals and a white collar. It is magnificent in pots.

• Flowering time August to December
• Height at maturity 40 cm

See the product sheet

Ils se distinguent par de grandes fleurs, doubles et amples, composées de nombreux ligules plus ou moins larges et plats aux extrémités arrondies ou légèrement frisées. C’est un groupe très hétérogène dans lequel on trouve des géants avec des fleurs dépassant les 20 cm de diamètre comme des sujets plus petits portant des fleurs évoquant les camélias, les nymphéas ou encore les chrysanthèmes.

Dahlia Café au Lait

We love its enormous cream flowers, a rare colour among dahlias.

• Flowering time August to November
• Height at maturity 1,20 m

See the product sheet

Dahlia Duke Duweno

A rare variety with intense purple pompons.

• Flowering time August to December
• Height at maturity 80 cm

See the product sheet

Dahlia Happy Butterfly

An amazing variety with yellow water lily flowers flamed with red.

• Flowering time August to November
• Height at maturity 1,10 m

See the product sheet

Ce sont ceux qui portent les plus grosses fleurs. D’allure majestueuse, on les voit de loin avec leurs tiges culminant à près de 1,50 m et leurs fleurs énormes de la taille d’une assiette pouvant aller jusqu’à plus de 35 cm de diamètre ! Avec leurs coloris subtils ou intenses, ils sont spectaculaires en arrière-plan d’un massif de vivaces ou au potager. Il est souvent nécessaire de les tuteurer.

Dahlia Myrtle's Folly

We love its frizzy peach flowers edged with lilac pink.

• Flowering time August to November
• Height at maturity 1,20 m

See the product sheet

Dahlia Barbarossa

Its enormous scarlet flowers will be the focal point in the garden!

• Flowering time August to November
• Height at maturity 1,20 m

See the product sheet

Leur petite taille les rend incontournables pour une culture en pot, en jardinière ou groupés en bordure de massif. Ce groupe réunit les Dahlias Gallery, d’une taille d’environ 45 cm, ils offrent une floraison continue aux couleurs et aux formes opulentes, les cactus nains, de 50 à 60 cm, sublimes avec leurs grosses fleurs doubles colorées et la collection Happy Single aux fleurs simples vibrantes de couleurs qui ne dépassent pas les 60 à 80 cm.

Dahlia Happy Single Juliet

Its single candy pink flowers contrast beautifully against purple foliage, stunning!

• Flowering time August to November
• Height at maturity 60 cm

See the product sheet

Ils sont caractéristiques avec leurs inflorescences construites en boules parfaites, présentant une structure alvéolée évoquant un nid d’abeille. Ce qui différencie les pompons des balles, c’est la taille des capitules : les fleurs des dahlias pompons sont plus petites (10 cm maximum) que celles des dahlias balles, qui vont de 6 à 12 cm. Ces fleurs sphériques sont parfaites pour créer des bouquets tout ronds et animer les massifs d’une touche graphique et colorée.

Dahlia Pompom Burlesca

A safe bet with its beautiful tangy pink colour tinged with orange.

• Flowering time August to November
• Height at maturity 90 cm

See the product sheet

Dahlia Icoon

Beautiful sunny effect with its bright yellow flowers tipped with ruby.

• Flowering time August to November
• Height at maturity 1 m

See the product sheet

Planting dahlias

When to plant?

With Dahlias, there’s no need to rush; you must plant on time: if planted too early, the first shoots may be devoured by slugs. The tubers stored safely during winter are planted in spring, in March after the last frosts. In cold regions, wait until late April or early May, as soon as the soil is warmed and can be worked. Simply store the purchased tubers in a frost-free place until the right planting time.

Where to plant?

Dahlias grow almost everywhere in France. The essential condition for having flourishing dahlias is to plant them in the sun. The second requirement: ensure they have well-drained soil where water does not stagnate, especially in spring and autumn. Dahlias prefer light soils that remain cool and sufficiently moist with a good mulch during the growing season. Stagnant moisture, on the other hand, would encourage the rotting of the tubers.

While they can develop in any soil that is not too acidic or calcareous, they thrive in good fertile garden soil, rich in humus, cool, and well-drained, preferably with a neutral tendency. Dahlias are greedy: to bloom well and gain vigour, they need a good base fertilisation. If you have doubts about the nutritional qualities of the soil, fertilise (with compost or manure) in autumn.

Dahlias can be planted in borders as well as in the vegetable garden

Large Dahlias do not withstand strong winds or heavy rain well. A too windy situation could dry out the foliage and especially cause the stems to bend. It is better to reserve a sheltered spot from prevailing winds. For tall Dahlias, staking may be essential to support the heads, to prevent the stems from breaking at the slightest gust of wind, especially if they are planted alone. To prevent their flower stems from collapsing in the middle of the border, it is also preferable to plant Dahlias with other plants and bushes, which they can lean on.

When planting, allow enough space for them in your border compositions. Ensure that each plant remains easily accessible for fertilising, staking, pinching, and wintering.

While they fit into all garden settings, both in the vegetable garden and elsewhere, Dahlias truly shine as background or mid-border plants, adding a vibrant splash of colour.

Dwarf varieties are more suited to sunny flower beds, pathway edges, or pot cultivation on a sunny terrace or balcony. Potted plants should be planted in good potting soil and must be watered very regularly and receive a good bulb-specific fertiliser.

How to plant?

Dahlias are very demanding. To meet their requirements regarding soil nutritional qualities, it is better to loosen the soil in autumn with a base fertilisation or just a few days before planting. If your soil is too heavy, add potting soil and gravel to a soil where water tends to stagnate.

Planting the tubers

Around mid-April, as soon as the soil can be worked deeply, plant your dahlias.

• Space large dahlias 80 to 100 cm apart.
• Space small varieties 30 to 50 cm apart.
• Work the soil to a width and depth of 20 cm, mixing, for example, a handful of roasted horn powder or dehydrated blood into your well-crumbled garden soil. Dahlias are greedy: they need a good base fertilisation.
• Position the tubers so that the collar is 5 cm below the soil level.
• Cover them with about 10 cm of soil.
• Place stakes for the taller species, being careful not to damage the tubers; this will also help you locate where you buried your dahlias!
• Water abundantly and then regularly for the first 6 weeks to aid rooting.
• Scatter some slug pellets at the base of the planted tubers to allow the first shoots to emerge.
• Then mulch the soil once the recovery is assured.

→ Read also: Planting Dahlias, 8 common mistakes to avoid and How to force Dahlias to bloom earlier?

Wintering of dahlia tubercles

Dahlias are extremely frost-sensitive and fear frost. In regions with harsh winters where the thermometer regularly drops below -5 °C, lifting is obligatory if you want to keep them alive. In regions with mild winters where frosts are light and infrequent and in well-draining sandy soil, the tubercles can remain in place for the winter simply protected by a good mulch of dry leaves or straw. Lifting allows for the division of the tubercles and potting for earlier flowering.

At the end of October, beginning of November (not before, as the roots would not have sufficient reserves for the winter), when the plant weakens and the first frosts begin to blacken the leaves, it is time to unearth the tuberous stumps. The goal is simple: to protect them from frost!

• As soon as the foliage is blackened by frost, cut the stems to 15 cm above the ground.
• Gently unearth the tubercles using a garden fork.
• Remove as much soil as possible from between the tubercles.
• Label each stump at the base of the stem so you can easily recognise the plants in spring.
• Place the bulbs on a layer of turf, dry sand, or dry leaves in a cardboard box or a deep crate.
• Cover the tubercles with a layer of turf or dry leaves.
• Store them away from light, draughts, rodents, and… especially frost in a dry, cool, well-ventilated, and dark place where the temperature should not exceed 4 to 5°C (dry cellar, garage, or frost-free attic). Under these perfect conditions, dahlias keep very well, with almost no risk of loss.
• Regularly check the condition of the plants to detect any diseases.

→ Read also: How to winter dahlias to protect them from frost? and Wintering Dahlias: Should You Lift Them?

Maintenance and care

Dahlia is relatively easy to grow, but requires some attention. A few simple actions will ensure you have a flowering summer.

• In spring, protect the young shoots from slugs.
• During the growing season, Dahlia is thirsty for water. Water abundantly during the growth of the buds.
• In July, mulch with a 2 cm layer of dry straw or turf to maintain moisture throughout the summer. Water the mulch.
• Support the stems of larger plants if necessary as the plant develops.
• Tie up the young stems.
• 2 to 3 weeks after planting, pinch the terminal shoot to ramify the plant and increase flowering, especially if the tubers only provide a single stem. This will spread the habit of the plant, offering more resistance to the elements and possibly eliminating the need for unsightly staking.
• To achieve larger flowers, pinch off the side buds afterwards.
• Remove the small shoots in the axil of the leaves: the heads will be larger as a result.
• Remove faded flowers to encourage the appearance of new blooms and extend the flowering period.
• Water very regularly, and twice a week in case of high heat, at the base of the plant and not on the foliage.
• At the end of summer, apply organic fertiliser to promote growth.
• In autumn, incorporate a good amount of manure or well-matured compost into the garden soil.

Pests and Diseases

Dahlia fears attacks from slugs which, in spring, will devour its young shoots; fern juice or wood ash will make them flee. Later in the season, aphids may attack the young stems bearing buds: combat them with diluted black soap. Earwigs, on the other hand, love the tender petals, but their voracity does not harm the health of the plant. The plant may show signs of deficiency (thin stems, yellow leaves, small size) due to a lack of nutrients; apply a compost mulch and a complete fertiliser. Grey rot can affect the tubers in cases of excessive moisture.

→ Learn more about dahlia diseases and pests in our advice sheet!

Multiplication

By propagation by cuttings

This is the best way to obtain a large number of plants, but it is quite tedious; we recommend dividing your tubercles instead. Propagation by cuttings is done with tubercles that have been pre-sprouted. At the beginning of March, take the roots that have been stored all winter and place them in a new mixture of compost or moist turf. Three weeks will be needed to see shoots appear. Cuttings will be taken when these shoots are about ten centimetres long. Potted under a cold frame and then repotted, they can be planted in the ground at the beginning of June.

By division of tubercles

This is the simplest method. It can be done just before planting.

• In spring, at the end of March, take the roots that have been stored over winter
• Divide the tubercles into two or three pieces with a sharp knife or pruning shear, ensuring that each piece has a part of the old stem with an eye, from which the new shoots will emerge.
• Cover the wounds with charcoal.
• Only plant in mid-April to early May if small buds have appeared; otherwise, wait and water to encourage their appearance.

Discover our video tutorial on dividing dahlias:

To learn more, check out our tutorial: Multiplying Dahlias: the right techniques. Read also: How to sow Dahlias?

Associate

Incontournable des jardins de curé, le Dahlia est un florifère polyvalent qui apporte couleur, relief et originalité aux beds, rockeries, flower borders as well as the vegetable garden. Le Dahlia se cultive en isolé mais is preferably planted in groups in the middle or background of a sunny bed, associé à des graminées (Panicum, Molinia, Calamagrostis), à d’autres vivaces à fort développement (Cosmos, Asters, Echinacées, Cannas) qui joueront les souteneurs, empêchant leurs hampes fleuries de se coucher de façon disgracieuse.

Dahlias ‘Purple Flame’- Calamagrostis – Asters – Echinacées-

Les Paysages, les Mini-balles ou les Honkas aux pétales pointus composeront des scènes légères. On réserve les Gallery et les variétés naines Happy Single  ou les Dahlias collerette (‘Impression Fantastico‘ aux bordures ou aux jardinières. Magnifiques en massif, les Dahlias décoratifs, feront excellent cut flowers for bright and colourful summer bouquets.

Envie d’un peu plus d’inspiration ? Découvrez notre fiche conseil : “Dahlias, how to associate them well in the garden”