By Paul A. Thomas
University of Georgia
Hundreds of varieties have flowers ranging from 1 to 14 inches across on plants from 1 to 8 feet tall. Dahlias can give you almost any color of bloom you want in Georgia except true blue.
Treated properly, Dahlias grow very well in north Georgia and the state's piedmont area. They're harder to grow in the south Georgia coastal plain because of its longer period of high summer heat.
To grow dahlias, consider first how much space you're willing to dedicate to them, since they grow up to 8 feet tall. Typical plants are 3 to 5 feet tall.
Most catalogs and specialist nurseries also classify dahlias by such things as early, typical or late blooming and whether they're best for cut flowers or exhibition blooms. For a more in-depth breakdown, consult the Dahlia Society of Georgia (www.dahliasocietyofgeorgia.com) or American Dahlia Society (www.dahlia.org) or a catalog.
When to plantDahlia tubers are typically sold in later winter and spring. Many mail-order nurseries accept orders until late spring. Tubers are often planted in April in south Georgia and May in north Georgia. June plantings often give the most perfect fall flowers.
If you plant tubers early, you can take cuttings from them in May to produce a late-flowering crop.
Dahlias thrive in the sun. They'll do best if they get at least a half-day of direct sunlight. And they need at least six to eight hours of direct light produce good blooms.
Seldom will plants do well in heavy shade or in competition with trees. However, in the heat of the coastal plain, some shading from the intense heat of the afternoon sun is a great benefit. Protection from high winds is helpful, too, as the plants put up a lot of tender top growth.
The ideal soil for dahlias is one that's loose, holds moisture well and provides good aeration. The best pH is between 6.0 and 6.5.
When to feedDahlias are heavy feeders and develop large root systems. It's best to fertilize with liquid garden-plant food every four weeks by the manufacturer's directions.
You can use 10-10-10, but you must water it in and absolutely must not let it touch the stems and leaves, as it will burn the tissues and invite disease. Don't apply any fertilizer as the end of the season approaches.
To plant dahlias, place the tubers 4 to 6 inches deep. Put the tubers on their sides with the eyes facing upward. Cover them with 2 to 3 inches of soil. Be generous in spacing. Some of the small bedding varieties can be spaced 12 inches apart but usually require 2 feet on each side. The larger varieties need 3 to 4 feet of space between plants.
When the young plant has produced three or four pairs of leaves and is several inches high, pinch out the tip. This will cause the shoot to branch and produce side limbs.
You'll be in for a big disappointment if you don't stake your dahlias. Since many of the larger varieties grow tall, they can't support themselves when they reach maturity.
Make stakes 5 to 6 feet long and drive them about 1 foot into the ground. When the plants are about a foot tall, tie them to the stakes with soft string or cloth strips. Repeat about once a month as the plants grow taller. The limbs that bear the flowers especially need support.
To put dahlia flowers in a vase, cut them only in early morning (best) or late afternoon to prevent wilting. Place the flowers in tepid water immediately after cutting.
(Paul Thomas is a Cooperative Extension horticulturist with the University of Georgia College of Agricultural and Environmental Sciences.)