|Dahlia 'Awe Shucks'|
Dahlias are bushy, tuberous, herbaceous perennials related to sunflowers, chrysanthemums and zinnias. After 200 years of cultivation, selective breeding and hybridizing there is an astonishing array of forms, sizes and color combinations. Wikipedia notes there are 36 species (other sources say 15-20 species; there continues to be disagreement about classification) and 20,000 cultivars. Dahlias are octoploids, i.e., they have eight sets of homologous chromosomes, whereas most plants have only two; this is one reason there is such great diversity of color, form and size. Few dahlias are fragrant, but they all have a long bloom season and most make excellent cut flowers.
Dahlias are often grouped by size of bloom from Pompon and Mignon Singles measuring up to 2 inches in diameter to the Giants that have dinner plate size blooms measuring over 10 inches. There are 20 forms (also known as “classes”) recognized by the American Dahlia Society including Water Lily; Straight, Incurved and Semi Cactus varieties; Ball and Pompom; Peony-flowering; and Novelty types. You’ll find dahlias in almost every color except black and blue (which is fine by me!) including many bi-colored and variegated blooms. To date, 99 cultivars have gained the Royal Horticultural Society’s Award of Garden Merit.
Dahlia 'Brittany Rey'
Dahlia 'Bumble Rumble'
Dahlia 'Fuzzy Wuzzy'
Dahlia 'Ryn Fou'
Dahlia 'Show & Tell'
Dahlia 'Tiki Torch'
Dahlia 'Walter Hardistey'
Dahlia tubers are hardy to USDA Zone 8, but they can be lifted and stored in cool, frost-free conditions during winter. During the growing season, they need well draining soil and full sun. Taller cultivars usually require some form of staking. All require deadheading for continuous blooms and to keep the plants tidy (but you’ll be cutting them anyway to decorate your home and share with friends and family).
Slugs, particularly in spring, can be a serious pest to new growth and earwigs can disfigure the blooms. You might also have to deal with aphids, spider mites and powdery mildew.
In honor of the new school year, read on for a bit of dahlia history and geography lesson:
The mountain regions of Mexico and Central America are the birthplace of the Dahlia and in 1963 it was declared the national flower of Mexico. The flower was first cultivated by the ancient Aztecs that inhabited the region. Spanish botanists accompanying the conquistadores documented the early dahlias. Over time, seeds and tubers were distributed throughout Western Europe from stock grown at the Royal Botanical Gardens in Madrid, Spain. The earliest dahlias were gathered in the wild and cultivated for their tubers. In fact, today’s Oaxacan cuisine still incorporates dahlia tubers. A mocha-tasting extract from roasted tubers is used to flavor beverages throughout Central America. Hollow stems of an ancient 20-foot tall variety (D. imperialis aka the tree dahlia) were used to haul and/or provide water. The Aztecs called them “Acocotli”, or water-cane, and apparently used them to treat epilepsy.
The plant was named after Swedish botanist Anders Dahl, most likely by Abbe Antonio Jose Cavanilles, Director of the Royal Gardens of Madrid. The abbe is credited with scientifically defining the genus having received the first specimens from Mexico in 1789 and naming the first three species that flowered from the cuttings. It’s uncertain when the dahlia was introduced into cultivation in the U.S., perhaps in the mid-1800s.
Swan Island Dahlias is the largest and leading dahlia grower in the United States and has been in operation for over 85 years. The Gitts family has owned and operated the business for over 40 years. They hybridize their own new varieties, planting over 30,000 seedlings each year. From those original seedlings, it takes about 4 years to introduce a new seedling for sale. Each season, anywhere from 5 to 15 new varieties are introduced. They grow over 350 varieties on 40 acres in Canby, Ore., that are open to the public during blooming season.
Sources: www.aztecdahlias.com/azdahlhistory.htm, http://en.wikipedia.org/wiki/Dahlia, http://www.stanford.edu/group/dahlia_genetics/dahlia_history.htm, http://arnoldia.arboretum.harvard.edu/pdf/articles/1705.pdf