Plant Profile: Dahlia

Dahlias are the stars of the late summer garden. If you attend any county or state fair in the fall, you’re likely to encounter a stunning variety of dahlias. The spectrum of colors, sizes, and shapes is truly remarkable. For a comprehensive overview of the different classifications and hues, visit the American Dahlia Society's website.

There are 42 recognized species of dahlias, available in nearly every color imaginable: white, various shades of pink, red, yellow, orange, purple, and numerous combinations of these hues. The forms of these flowers are equally impressive, ranging from delightful single, daisy-like blooms to the popular double varieties, which can measure anywhere from 2 inches to a striking 12 inches in diameter. Dahlias are categorized into ten distinct groups: single, anemone, collarette, waterlily, decorative, ball, pompon, cactus, semi-cactus, and miscellaneous, with the peony and cactus forms being particularly breathtaking.

Dahlias thrive in gardens with rich, well-drained soil and ample sunlight. As hybrids, they are primarily planted as tuberous roots, although seeds for mixed, small-flowered types are also available. It’s best to plant the tuberous roots or young plants around the time of the last frost, spacing them 1 to 3 feet apart, depending on the variety. For a more visually appealing display, plant them in groups of at least five. Taller varieties, exceeding 2 feet, may require staking or other forms of support. While dahlias may struggle during the peak summer heat, consistent mulching and adequate watering will ensure a vibrant display from late summer through fall, lasting until the first frost. Regularly deadheading spent flowers will help prolong their blooming period.

Although dahlias are technically herbaceous perennials, they are usually cultivated as annuals. In most areas of the Piedmont region and the western part of the state, the tuberous roots will not survive winter in the ground, so gardeners in these regions should plan to dig up the roots in the fall for winter storage. However, dahlias are hardy in the Raleigh area and extend to the coast.

When planting, ensure that tubers are covered with about 3 inches of soil. Be aware that these plants can be damaged if temperatures drop below 25 degrees Fahrenheit (2 degrees Celsius). When grown from tubers, dahlias tend to grow tall and may need staking. Alternatively, they can be cultivated from seed-germinated selections, but these are usually smaller, less heat-tolerant, and often exhibit inconsistent growth and poor flowering.

In terms of pests and diseases, dahlias can be challenging to grow and may face various issues, including infestations from aphids, leafhoppers, and caterpillars. They are also susceptible to diseases such as powdery mildew, root rot, crown gall, viruses, and wilts.