What Type of Light Do Dahlias Need?

Dahlias come in all different shapes, sizes and colors.

Dahlias originated in Mexico and Central America. They love warm soil and lots of sun. Dahlias that receive the right amount of light will reward you with brightly colored blooms in all shapes and sizes. Mass plantings of dahlias are especially striking, but they also work well as container plants and as a component of a cutting garden.

Basic Light Requirements

Dahlias thrive in full sun in a south-facing garden plot. Full sun will result in the best growth and impressive blooms. Some dahlias may tolerate partial shade but partial shade should really only be considered in the hottest climates with the most brutal afternoon sun.

Container Plants

Barbara Jenke of the American Dahlia Society recommends that tubers started indoors be grown under grow lights rather than relying on sunlight from a window. The benefit of using a grow light is that the height of the light is adjustable as the plants grow and the plants will grow up toward it rather than lean toward the window. Sunlight will work, too, but she recommends that the pots be turned regularly to encourage plants to grow straight up.

Seasonal Light

Colleen Paing, in her blog for SeattlePi.com, recommends that growers consider the bloom season and its light intensity when selecting which colors of dahlias to grow. Many dahlias are mid- to late-summer bloomers. The light at that time of year can be quite intense and can easily fade subtle bloom colors like pale pink and pale yellow. Strong, deep, bright colors, she recommends, stand up to late summer sun. Intense hues in light values---such as deep yellows and oranges---will steal the show in the warm light of fall.

Too Much Shade

One benefit of a lot of sun is that it keeps mildew at bay. Dahlia is an ornamental plant that is susceptible to powdery mildew, which develops on the foliage and leaves a whitish-gray dust-like covering on the leaves and on new buds. The spores that attack dahlias are called Erysiphe cichoracearum. Shade and moderate temperatures favor the growth of the spores. In addition to full sun, dahlias should be spaced 18 to 24 inches apart so they get the proper amount of air circulation. If your yard doesn't get the amount of sun that dahlias need and love, it's in your best interest to plant something that will thrive in part-shade, rather than battling mildew on your ornamentals.

Considerations

Make your dahlia choices in the late summer and early fall when they are in bloom so you know what you're getting. As Colleen Laing puts it, "Catalog photos and descriptions, no matter how beautiful and detailed, never seem to capture the real impact of these garden performers." Purchase your tubers from local dahlia dealers---especially if you're a dahlia novice---so you can be sure you're getting a variety that performs well in your area.

References

• The University of Florida Extension: Dahlia spp.
• Seattle Pi: Sound Gardens: Gardening Around the Puget Sound: Dahlias
• University of California Integrated Pest Management Program: Powdery Mildew on Ornamentals
• The American Dahlia Society: Growing Dahlias in Containers
• Early May: Roots and Bulbs: Dahlias