Regional Gardening Reports :: National Gardening Association

In the Garden:
Upper South
April, 2007
Regional Report

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Dahlias produce spectacular flowers, such as these unusual red-purple flowers of 'Amante'.

Dazzling Dahlias

Part of the folklore in my family surrounded the dahlias that my father grew as a 20-something. By the time I came along, he had moved on to other flowers. Still, the tales of the giant flowers he grew always intrigued me, and among my garden orders this spring was one for a collection of six dahlia varieties. Now, as I read the press releases from the Netherlands Flower Bulb Information Center, (, I learn that dahlias are once again becoming trendy garden plants. Why I've waited so long to grow them, or why they ever fell out of general popularity is hard to say, because few flowers rival these mid- to late-summer classic flowers.

Whether they boast dinner-plate-sized flowers or diminutive 2-inch blossoms, dahlias offer more flamboyance per plant, and in more varied colors and shapes, than most other garden plants (only tulips top dahlias in number of colors). If you can dream up a dahlia look, it probably exists. Choose from nearly every color under the sun (except true blue or black), including multicolored ones, and from flower types as varied in shape and form as cactus, water lily, pompon, single, anemone, peony, and more. In fact, there are thousands of named varieties.

The mature height of dahlias also varies, from about 12 inches tall to 5 feet or more, making them versatile players in the garden, from front-of-the-border standouts to stately background plantings. Dahlias also make excellent cut flowers for bouquets, typically lasting about a week if cut early in the day just as they first open.

Getting Started
Native to Mexico, dahlias grow from tubers that somewhat resemble sweet potatoes. You'll find tubers available locally at the garden departments of discount and home improvement stores, as well as in garden centers, which usually sell plants as well as the tubers. Many garden catalogs also carry at least a few varieties, while specialist companies offer a wide range of dahlia colors and types. Short-growing dahlias, usually referred to as bedding dahlias, are usually started from seed, but the resulting tubers can be kept from year to year.

Dahlias are sensitive to freezing temperatures, so they should not be planted outdoors until the threat of frost has passed and the soil is about 60 degrees F. They can, however, be started indoors in pots to get a jump on the season, then transplanted to the garden when warm enough.

In the Garden
Dahlias grow best and produce the most flowers when grown in a full-sun location in rich, well-drained soil with a pH of about 6.5. Before planting, work some compost or peat moss into the soil as well as a complete fertilizer that's low in nitrogen. The shorter-growing types of dahlias should be spaced 9 to 12 inches apart. Those that grow about 3 feet tall are spaced 2 feet apart, while the tallest types are spaced 3 feet apart.

Prepare a planting hole 12 inches deep and 12 inches in diameter. Then partially fill the hole until it is about 6 inches deep. Place the tuber horizontally in the bottom of the hole with the "eyes" pointing upward. For taller-growing types, insert an appropriate-sized stake next to the tuber at planting time to avoid damaging the tuber later. Cover the tuber with 2 inches of soil and water thoroughly. As the sprouts emerge from the soil, gradually add soil until the hole is filled. As the plant grows, attach it loosely to the stake, adding more ties as needed.

Because dahlias have shallow roots, applying an organic mulch, such as well-aged compost, is important. Water plants during droughts but avoid wetting the leaves. Fertilize dahlias monthly until mid-August. Slugs can be a problem, so take appropriate precautions.

Dahlias begin flowering in July and continue until the hard frosts of autumn. In areas colder than Zone 7, dahlias are considered to be tender bulbs that will not survive exposure to harsh winter weather. In these regions gardeners can either let the plants die and compost them, or dig and store the bulbs over the winter, then replant into the garden next summer. Wait about a week after the plant has died back before digging in order to allow new sprouts to develop for next year. Gently wash and dry the clump of bulbs, place in a box filled with sawdust or vermiculite, and store in a dry area at about 40 to 55 degrees F.

Pinching and Pruning
You can shape dahlias by pinching and pruning. On low-growing varieties, pinch back the new growth several times to promote compact, bushy growth. For the largest flowers on tall types, remove all of the side buds at the end of each branch, leaving only the central bud. Or do only minimal pruning for more flowers that are a bit smaller.

Whatever types or colors of dahlias you chose, they will surely reward you and inspire you to make them a regular addition to the garden.

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