All about Dahlias

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The dahlia is extremely varied in flower color and shape. The only color that does not occur in dahlias is blue, otherwise you can find all colors in all combinations. The variation in flower shape is so great that over the years dahlias have been classified into groups.

There is no other plant for which so many cultivar varieties have been cultivated. Which dahlias should you choose, where should you plant them and why? The more you know about dahlias, the more beautiful they become. In this article, you will learn everything about the dahlia.

History

The dahlia has a long history. These plants do not occur naturally in the Netherlands and are unlikely to escape from a garden and become wild because dahlias are not hardy. The plant must therefore originate from a warm country. That country is Mexico.

In 1570, King Philip II of Spain sent his physician Hernandez to Mexico to study the plants and animals there. He discovered plants with filled flowers in many colors that the Aztecs called 'acocotli'. The plants he described were dahlias. Drawings from that time only depict filled flowers and no single flowers. You cannot ask Hernandez anymore; he probably did not find wild dahlias but cultivated ones in the gardens of the Aztecs. They used dahlias as medicine and ate the tubers.

In the past, life was slower, and it took centuries for information from other countries to arrive. It wasn't until 1789 that the director of the botanical garden (gardens with a scientific character) of the city of Mexico sent the first dahlia seeds to Abbé Cavanilles, a staff member of the Botanical Garden of Madrid. Cavanilles managed to grow plants from the seeds. These plants had purple and red flowers. He named the plant dahlia after the Swedish botanist Andreas Dahl.

Dahliarage

From that time on, dahlias gained popularity rapidly. Explorers, well-known and lesser-known growers, and even Empress Joséphine – wife of Napoleon – collected the colorful flowers and continually discovered new colors.

From 1820 to 1860, dahlias were so popular that there was a 'dahliarage'. The dahlia was then a true show flower, and dahlia exhibitions were held everywhere in Europe (especially in England).

New dahlia’s

In the course of history, tens of thousands of dahlias have been bred by professional growers and enthusiastic amateurs. By 1936, there were already about 30,000 named dahlias, and by 2004, over 50,000. But not all of them are still available. Each dahlia seemed more beautiful than the last, and new ones replaced the old ones.

The oldest dahlia still being grown today is the English 'White Aster' from 1879 and the German 'Stolze von Berlin' from 1884. Dutch growers have traditionally introduced many dahlias. They often gave them Dutch names: 'GF Hemerik' from 1936, 'Gerrie Hoek' from 1946, and the well-known 'Glorie van Heemstede' from 1947.

The Netherlands has been a leading country in the field of dahlias for years, and these colorful flowers are once again in the spotlight.

Parades and Garden Enthusiasts

Just as diverse as dahlias themselves are the interest groups that are involved with dahlias for one reason or another. Participants in dahlia parades grow their own dahlias because they know exactly which colors they need and which dahlias perform well. Members of dahlia societies cultivate perfect dahlias to win prizes at shows. Dahlia breeders (individuals who select plants with the best hereditary traits and develop new varieties) breed dahlias and provide colors that don't exist yet, with sturdy stems for vases or with dark foliage. Garden enthusiasts want a row of dahlias in the vegetable garden for cutting, a few low growers for pots, and dark-leaved varieties for the border.

Garden Dahlias

Dahlias used for exhibitions are not all suitable for borders. Prizes at shows are won with perfect specimens where the focus is mainly on the flower. The foliage plays a subordinate role. If you want to combine dahlias with other plants, dahlias with dark, finely cut leaves are often chosen.

One of the first dark-leaved dahlias, 'Bishop of Llandaff' (see photo below) from 1928, caused a major breakthrough in the use of dahlias in borders about a decade ago. The 'bishop' with its semi-double scarlet flowers captured the hearts of garden enthusiasts.

The Bishop's Children

The old bishop was joined by his offspring. The children of the bishop all have dark foliage and, besides dark red, come in purple, orange, yellow, and two-toned varieties. 'Bishop of Dover' has single, ivory-colored flowers with a hint of lilac. Dutch and English breeders have produced more beautiful dark-leaved cultivars that, due to their looser, more natural growth habit, fit excellently in a border.

Flower

We refer to them as dahlia flowers, but actually, a dahlia flower is not one flower but composed of different florets that together form a flower head.

The central florets are the tube florets, and the florets around them are the ray florets. The tube florets form the heart of the flower, and each floret contains a pistil and stamens. The ray florets are more conspicuous and may or may not contain a pistil.

Dahlias are pollinated by bees and bumblebees. Double-flowered dahlias consist only of ray florets.

Root Tubers

Dahlias have swollen roots underground, known as root tubers. The buds are located on the top of the root tuber. So, you cannot plant a piece of root tuber in the ground and expect it to sprout.

There must always be a bud on a piece of root tuber. These buds are also called eyes, reminiscent of potatoes. The root tuber of a dahlia is a thickened root and does not have eyes.

The root tubers of certain dahlia varieties are still cultivated as a food crop in Mexico, but their taste and texture are not particularly appreciated in Western countries.

Order in Affairs

Our garden dahlias do not occur naturally in the wild anywhere; they are all cultivated products, which we call cultivars or cultural varieties. Because they cannot be traced back to one species, order has been established by classifying them into groups.

The groups are classified according to the shape of the flower, which is determined by the model of the petals. In a number of groups, distinctions are made in five sizes, namely:

Giant XL
Large Flowered (Large L)
Medium-Sized (Medium M)
Small Flowered (Small, S)
Miniature (Miniature XS).

The XL dahlias are also called 'dinnerplate' dahlias. With the five different sizes mentioned, we follow the classification of the English Royal Horticultural Society (RHS). This classification is clear, and the fun part is that as you search for dahlias, you discover your preferences.

For example, a natural garden owner may choose single-flowered, star, or peony-flowered dahlias because their open hearts attract bees.

Classification, Grouping

Below you will find the fourteen groups in which dahlias are classified. For each group, you will find an image of a specific dahlia that accurately represents what we are talking about.

1. Single-flowered Group

An open center of tubular florets surrounded by a single row of ray florets.

2. Anemone-flowered Group

A center of tubular florets that have grown in such a way that they completely fill the center. The center is surrounded by one or two rows of ray florets.

3. Collar Group

Surrounding the heart, a wreath of ray florets with fairly large flat petals, inside of which are one or more wreaths of ray florets with much smaller petals, forming the collar.

4. Waterlily Group

Fully double flowers where the center is not visible. The broad, sturdy petals are horizontally positioned on the outer edge and slightly upward in the middle.

5. Decorative Group

Fully double flowers with petals arranged in layers. The petals are wide and flat, rounded or slightly pointed or lobed at the tips.

6. Ball Group

Spherical, slightly flattened, densely filled flowers. The petals have a blunt tip and are rolled inward for more than half, forming a horn-like shape.

7. Pompon Group

Similar flowering habit as ball dahlias, but the petals are more tightly folded, smaller, and rounder. The flowers are rounder than those of ball dahlias.

8. Cactus Group

Fully filled flowers with pointed narrow petals that are rolled outward for more than half along the longitudinal axis.

9. Semi-cactus Group

Fully filled flowers with pointed petals that are rolled outward from the top to halfway or less along the longitudinal axis. The difference between cactus and semi-cactus dahlias is not always easy to discern.

10. Other Group

This group includes all dahlias that do not belong to any of the previous groups.

11. Fringed Group

The tips of the ray florets are pointed at the top, creating a fringed effect.

12. Star Group

Open center surrounded by narrow ray florets.

13. Fully Double Star Group

Strongly double flowers without a center.

14. Peony Flowered Group

Large flowers with three or four rows of ray florets around an open center of disk florets.

Dahlias in the Garden

Dahlias are not difficult to grow. They thrive in almost any well-drained soil in a sheltered spot in the sun. The better they are cared for, the longer they bloom.

That's why dahlias were often grown in vegetable gardens because vegetable plants also prefer sheltered, sunny, and nutritious soil. In the border, it's sufficient to add good garden soil or compost to the planting hole.

When they grow and bloom vigorously, they appreciate a handful of bone meal or strawberry fertilizer. Dahlia tubers can be ordered from February onwards, but they should not be planted outside in the open ground yet.

Dahlias can be planted from mid-April onwards. If there is still a risk of frost and the plant is just above the ground, cover it with an inverted flower pot. Tubers that have already sprouted and cuttings should only be planted after mid-May.

Slugs and Supports

You can't blame the slugs for being fond of young dahlia shoots (a new stem with leaves and/or flowers). Once the plants are growing, they are no longer bothered by slug damage.

You can also plant dahlias in a pot first and only put them in the garden when they are well established. A ring made of a pet bottle or copper can be placed around the emerging plants in the ground, which helps to deter slugs. Make sure dahlias always receive enough water.

Always remove the faded flowers, including the stem, otherwise they will stop blooming and focus on producing seeds. Harvest bouquets regularly; the more you harvest, the more they bloom.

Support tall varieties in time - before they fall over - with brushwood (branched prunings) and place them in the border among companion plants so they support each other. Dahlias can remain in the ground until the first frost, which is often around the end of September.

After that, remove them from the ground, cut off the stems, and let them dry for a few days (upside down). They can be stored in a cardboard box (filled with sawdust or straw) in a frost-free, dry place where there is no draft, otherwise the tubers may dry out.

Potted Plants

The smaller and lower dahlias are excellent potted plants for balconies or terraces. After the blooming season and before the frost, the pots can overwinter indoors in a frost-free place. They can remain in the pot and do not need water during this time. In spring, take them out of the pot and give them fresh soil for a new blooming season.

Dahlia Gardens

In the gardens of Keukenhof Castle in Lisse, you can admire over 150 dahlias from mid-July to mid-October. At the CNB Show Garden in Voorhout, growers and breeders showcase their dahlias. (CNB: Cooperative Dutch Flower Bulb Centre). Every year, the Holland Dahlia Event is held, offering more places to view dahlias besides these two locations.

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