Dahlias: Part One

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My first experiences with dahlias was nearly 20 years ago, but it was in a big way. I was the manager of a large production nursery and one of our seasonal crops was huge potted dahlias. The roots would arrive from Holland and the West Coast in early spring and were immediately potted in a warm greenhouse, where they were fed and forced for several months.

By mid-May we had fully budded and flowering plants for sale that stood 4 and 5 feet tall. But I never got to see them in full bloom. That all changed when I moved upstate to work in a private garden where we forced and planted more than 50 varieties of garden dahlias that bloomed from June through October; and in really great years, even in November.

While generally unscented, these plants make up for it with spectacular flowers that cover the entire color spectrum with blooms from an inch in diameter to 6 inches and more. If that isn’t versatile enough for you, how about heights from just several inches tall to over 6 feet. Don’t forget to add the special dividend that the tuberous types are recyclable—usable year after year with some easy care and dormant-season storage.

The dahlia is native to the New World, discovered by Spanish explorers during the Aztec empire. The ancestral origin of today’s dahlia grew wild in Mexico and Central America. The Aztecs knew the dahlia as a tall (5 foot) plant that produced small, blood-red flowers.

In 1519, the Cortez expedition discovered the dahlia and called it “cocoxochitl.” Collected as a New World plant, the dahlia survived the journey across the Atlantic to be tended in Spanish monastery gardens.

No one could foresee the intense rivalry that would develop among the European royalty for this flower. The dahlia became a treasured status symbol for Empress Josephine, wife of Napoleon, who obtained seed that had been stolen from the Spanish. She haughtily refused to share the plant with anyone. But when a member of her court stole some of the tubers, the selfish Josephine became enraged and banned the innocent dahlia from her gardens.

The Abbe Antonio Jose Cavanilles of the Royal Gardens in Madrid sent seeds of the cocoxochitl to Anders Dahl, a noted Swedish botanist. Mr. Dahl had visions of the plant tubers to be a new and useful vegetable similar to potatoes. He was sorely disappointed to learn the tubers were inedible. Still, he was intrigued, and began selecting plants, crossing plant lines and creating new plant forms.

The Spanish took a revived interest in this plant. Wanting to reestablish their claim to the discovery, in 1789 the King of Spain held a festival to celebrate Spain’s “discovery” of cocoxochitl. Since the Aztec name was, at best, difficult to translate and pronounce, the King of Spain honored the Swedish botanist for his development of new plants, and renamed the plant “Dahlia.”

The Dutch and the English also competed over this must-have flower.

In 1782, a Dutch importer had arranged for a shipment of bulbs from Mexico. All but one died.

The English, in the meantime, had received some plants from the French. The dahlias were planted in the prestigious Kew Gardens in 1798.

By the turn of the century, interest in breeding work had intensified to the point that dahlias were widely planted in English and Dutch parks and other public places.

By the 1830s, the demand for the plants, seeds and tubers, soon outstripped the supply. Prices rose, and fortunes were made and lost in dahlias, just like what had happened during the “tulipmania” of earlier generations.

It was not until later in the 19th century, when the European garden demand was met, that shipments began to the United States during the American Civil War. When supply lines were cut, nurseryman Peter Henderson of New York City began producing his own dahlia seeds, tubers and flowers. This effort marked the beginning of dahlia breeding in the U.S.

During the past 85 years, breeding and production has centered in Washington, Oregon and California. In California, the climate and lack of rainfall during the harvesting season have made the Lompoc- and Santa Maria valleys extremely favorable for cultivation.

Breeding advancements have also continued in England, Holland and Japan. Even though modern breeding work continues, it is said that the descendants of the original wild ancestor cocoxochitl can still be found in the Guatemalan and Mexican uplands.

The dahlia is a member of the compositae—a vast family represented in all parts of the world by some 800 genera and many thousands of species, so named for their composite flowers. This family, the largest of all in the plant kingdom, includes such common kitchen garden vegetables as the lettuce and the artichoke, as well as flowering ornamentals. Among the flowering ornamentals in the composite family, in addition to the dahlia, are the friendly and familiar aster, chrysanthemum, cosmos, rudbeckia and zinnia, as well as the more arcane arctotis and tithonia.

The precise origins of today’s dahlia are probably the species D. pinnata and the species D. coccinea. The American Dahlia Society recognizes 12 groups of cultivars, based on external form and flower structure. Within these groups are thousands of named varieties. There are dahlia types with the flower for form, habit, height and color to suit virtually every garden need from pots and planters to towering specimens and tiny bedders.

Most experienced gardeners are familiar with the four popular dahlia forms: the cactus, pompon, double- and semi-double flowers—all of which can be grown from seed. Most gardeners though choose to purchase the mature tubers, which put on a much more dramatic show, except in the case of the dwarf varieties that can be grown from seed or as cell-pack plants that will perform well as bedding plants.

The cactus dahlia has spiky petals and is quite dramatic to view. Its star-like form means that it stands up well to inclement weather. This type of dahlia can be grown in patio pots or among herbaceous perennials in mixed borders. It likes full sun and can grow from anywhere between 18 inches and 2 feet.

The pompon bears short, tight, cup-shaped petals that create a rounded flower. The shape is similar to the decorative tuft used on clothing. The pompon flower is about 2 inches in diameter and is produced on plants that range from 3 to 4 feet tall.

The double- and semi-double flower forms are often exhibited in one mixture from seed. Environmental factors may influence the degree of doubleness in many of the flowers. The double flowers contain numerous rows of ray petals surrounding a central disc. The petals can be round or pointed on the ends. The semi-double flowers produce fewer rows of ray petals. Dwarf plants are available in double- or semi-double flower forms and may range in height from 10 to 20 inches.

Two other dahlia flower forms exist but are not extensively available. The single dahlia flower and the collarette type can be grown from seed. The collarette type consists of a single row of ray flowers with an inner collar of quilled petals. The inner collar petals can be the same color as the ray petals or a contrasting color.

Next week, we’ll briefly look at growing dahlias from seed but we’ll take a much closer look at the taller estate dahlias (available any day now at your local garden center), which can be some of the most striking flowers in the summer and fall garden. Keep growing.

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