An American Native - The Dahlia Family
Judy Ziemba, State Horticulture Chairman

Horticulture - Garden Glories July-August-Sept 2004

After the wonderful bounty of spring and June perennials, there are several families of plants the gardener can depend for color and form during the summer months. One is the versatile branch of the Composite Family called dahlias. For abundant bloom from July to frost, there is sure to be a dahlia that will work for you.

Dahlias are native American plants coming from Mexico and were used as an herbal treatment for epilepsy by the Aztecs. Before insulin was discovered to treat diabetes, a type of diabetic sugar was derived from dahlia roots. Once thought a possible substitute for potatoes during the potato famines, that idea was quickly dropped after one taste. Today the primary value is the beauty of the blooms.

Dahlias are divided into specific classes by the American Dahlia Society including pompoms, cacti, collarettes, singles, decoratives and others. For most gardeners, they can be sorted into three groups: tall, large flowered garden types, cut flower types and border/container types. The small varieties may be used, in flower boxes or containers while medium plants may be used in a cutting garden or among most perennials. Staking is required for the tall varieties or they may be planted near fences, trellises or arbors.

Plants require full sun, prefer steady moisture and will produce well with regular feedings until flowering. As cut flowers, they are long lasting and cutting encourages more bloom and bushier plants. Stems can be cut when the flowers are open or in bud and plunged in hot water to seal. Display arrangements near a sunny window, as the foliage will yellow if deprived of light and remove all underwater foliage. You can prolong vase life by adding 1/4 tsp. bleach and 2 tsp. of sugar to 1/2 gallon water and re-cutting stems every other day.

If you hope to exhibit dahlia blooms, regular disbudding is required to maximize flower size. Removing all buds except the terminal (top) bud causes each stem to put all the energy and vigor into the one bud, resulting in exhibition sized blooms. It takes about nine weeks for the terminal bud to open unless unusual conditions exist. Many varieties are wonderful for dramatic flower arrangements. Bicolors and blends are much favored as well as varieties with dark foliage.

The major pests encountered when growing dahlias are aphids, spider mites and thrips. Insecticidal soap spray and yellow sticky traps can minimize this trouble. Aphids make the leaves curl and leave a wet sticky film on the foliage. Spider mites thrive in hot dry weather and are hard to see but spotted or bronzing leaves, fine webbing and loss of vigor are the tell tale signs. Thrips are hard to see or catch and attack buds resulting in damaged blooms. Dahlias can succumb to fungal and viral diseases and wilts. Light yellow vein banding, rings or spots of yellow on leaves or wavy yellow lines give a clue to viral diseases. Stunted or abnormal growth also can indicate diseases and the best thing to do is to destroy the plant before it spreads the problem. Do not compost the plant but place in a plastic bag and put with household waste.

Propagating dahlias can be accomplished in three ways: seeds, tuber division and cuttings. Most of the small border/container types are easily grown from seed started in February or March and are ready to bloom the first summer. Larger sized varieties usually are grown from tubers that can be started indoors and planted out after danger of frost. Tubers can be planted directly in the garden but not before the last frost and if soil is cool, they will be slower to reach blooming size. Cuttings can be taken of 3-4" shoots and rooted in sand or soiless mix with rooting hormone to increase success. Only cuttings and tuber divisions produce plants identical to the parents.

The most often asked question about dahlias is how to lift these tender perennial tubers and store them over winter successfully. Even the bedding types will have a tuber or more which can be saved from year to year. The problems of storing tubers is that they are too warm and dry out and shrivel or they are too wet and mold and/or root. Most instructions indicate carefully digging the tubers, shaking off the loose soil and removing the soil with water. Allow cuts to dry, label and pack in sawdust or peat and store in a cool location. Check every month or so and sprinkle with water if shriveling appears or open and dry out if too wet. Most people do not have 100% success. When dividing tubers that have been successfully stored over winter, be sure to include a bit of the original stalk and at least one eye with each tuber.

With healthy tubers and a moderate amount of attention, dahlias can be a colorful addition to the summer and autumn garden.