Each year the National Garden Bureau designates one bulb or bulb-like plant to highlight and this year’s featured plant is dahlia. The dahlia genus was named by the Madrid Botanical Garden for Andreas Dahl, a Swedish botanist and student of Carl Linnaeus.
Mexico and Guatemala are the original homelands of dahlia species used to develop today’s garden cultivars. Spanish explorers of Central America brought home seeds, plants and roots. Initially plant breeders were interested in dahlia roots as a food source, since the flowers of native Mexican species were not very showy. But in 1872 a box of dahlia roots was sent from Mexico to Holland. The only surviving tuber produced brilliant red flowers with petals that were rolled back and pointed. These flowers caught the eye of plant breeders who crossed this plant with earlier species and began the development of the dahlias we know today.
Tremendous flower variety
The American Dahlia Society (ADS) categorizes today’s dahlias into groups based on flower size, form, and color. Dahlia flower sizes range from Giant -- over 10 inches in diameter, to Mignon Single -- up to 2 inches in diameter. Eighteen different categories group plants based on flower petal shape, arrangement and number. Flowers are available in 15 colors or color combinations, so there is a dahlia to fit any garden design.
With so many dahlia varieties to choose from it’s difficult to recommend just a few, but one great cultivar to consider is "Bishop’s Children," which has single and semi-double flowers in mix of red, orange, yellow, pink, purple and bicolored mixes. Flowers are 3 to 4 inches across, with dark maroon-black foliage, and plants have a mature height of 2 ½ to 3 feet. Seeds are available from Park Seed Company, parkseed.com
Dahlias grow from a thickened underground stem section called a tuber, which looks similar to a sweet potato but smaller. Gardeners can buy seeds and dormant tubers from many garden centers or mail order catalogues or purchase potted plants in spring.
No matter if you’re starting with seeds, tubers or plants, dahlias do not like cold soil and will be damaged by frost, so wait to plant them in the garden until danger of frost is past -- around early May in eastern Nebraska. Or if you want to get a jump on the growing season, you could start seeds or tubers in the house now by potting them in containers with a peat-based growing mixture and placing them under grow lights.
In the garden, choose a sunny location with well-drained soil for the best plant growth and flower production. Supplementing your soil with compost to provide additional organic matter and nutrients and improve soil tilth creates a better growing environment for dahlias. Mulch plants after establishment to keep soil cool and preserve moisture.
Dahlias benefit from regular fertilization during the growing season with granular or water-soluble fertilizers. Use a product high in nitrogen early in the season, then switch to a blooming-plant fertilizer about mid-June. Stop fertilizing at the end of August.
Tall plants, especially those with large flowers, benefit from staking to support the stems and keep flowers standing tall. Put stakes in place at planting to avoid damaging the tubers when inserting stakes later in the season.
If you are saving tubers each year, divide the tuber clumps in spring before replanting. Remove any dead areas, and make sure each division has at least one growing point or “eye.” Allow the cut sections to dry for a few days before replanting or potting. Plant the tubers with the eye pointing up.
Storing dahlia tubers
Tubers must be dug each fall before frost and stored in slightly moistened sawdust, vermiculite or peat moss. Choose a cool (50 to 55 F degree), dark location for storage. Check the tubers periodically during winter for rotting or excessive drying. If tubers get too dry they will start to wrinkle or shrivel. Dunk them in water and remoisten the vermiculite or peat moss so that it is slightly damp.
Or place dahlia tubers in perforated plastic bags with moistened vermiculite or peat moss, then place the bags in a larger container with additional vermiculite or peat moss to reduce moisture loss.
For more information on this year's featured plants, visit the National Garden Bureau. www.ngb.org.