Written by Nancy Polz, Portage County Master Gardener Volunteer
Just as summer starts to wane, dahlias step in to show their spectacular blooms. Dahlias are native to Mexico and Central America where their tubers were originally grown as an edible vegetable. At that time, the flower was unimpressive. Explorers took the tubers back to Europe where flower development was the interest rather than a food source. Dahlias are named after Swedish botanist Andrea Dahl. There are now more than 50,000 registered cultivars that are growing worldwide.
Dahlia flowers range in size from 2” (pompon) to greater than 10” (giant or dinnerplate), and 20 forms (such as decorative, cactus, ball, collarette, and more). Dahlias can be solid colors, striped, or multicolored.
In Northeast Ohio, the tubers of these sun-loving flowers can be planted directly into the ground after the soil temperature reaches 60 degrees. They can also be planted in pots or grow bags large enough to accommodate the numerous tubers produced over the summer growing period. Some dahlia plants remain short, but the majority grow to be 4’-6’ tall. Although these plants appear robust and strong, their stems are hollow and can break easily with strong winds.
Therefore, it is important to stake these plants, either with sturdy wooden or metal (conduit pipe, re-bar, or T-posts) stakes inserted one foot into the soil, or as growers with a large number of plants often use horizontal trellis netting or Florida weave (basket weave) to corral the plants and prevent them from falling over or breaking their stems.
Dahlia tubers will produce the exact flowers as the “mother” (original) tuber as will cuttings taken from the sprouts. Due to a basic eight sets of chromosomes and pollination, dahlia seeds will not produce the exact replica of the parent plant. Instead, a similar or totally different looking flower is created; thus, the result of 50,000+ cultivars.
As beautiful as dahlias appear, they do not come without challenges. Damaging insects such as Japanese beetles, thrips, earwigs, and slugs can destroy and disfigure the plants and flowers. Bacteria producing crown gall and leafy gall, and viruses producing dahlia mosaic disease and tomato spotted wilt disease will not only kill the plant but can spread to other plants with the same result.
Before treating and fertilizing dahlias, it is important to identify the issue. A soil test will determine the amount of nutrients and minerals in your soil, thus preventing over-fertilizing. Ohio soils tend to have a high phosphorous content (the “P” in NPK). Insects can be harmful or beneficial. It is necessary to identify the insects on the plants before any treatment, if necessary, should be done. When using insecticides, always read the label in its entirety and follow the directions correctly--” the label is the law.’
These gorgeous flowers can be enjoyed well into autumn when a killing frost will put an end to them. As a rule, in-ground tubers will not survive Northeast Ohio winters. Three choices are available: (1) dig and store the tubers till next spring (2) heavily mulch and take a chance (3) treat them as an annual and purchase new tubers for the next year.
For more information:
American Dahlia Society
Dahlia Society of Ohio
North Carolina Extension Toolbox - Dahlias
Dahlias Ohio State University Extension
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