Bright colors and dramatic forms make dahlias an exciting addition to the summer border.
Their long history dates back to the 1500s, when these tuberous perennials were discovered in the mountains of Mexico by Spanish conquistadors. More than 200 years later, dahlias made their way to Europe, where hybridizers began to work their magic.
By the Victorian era, so many types of dahlias existed that breeders developed a vocabulary to describe their blooms.
Dahlia hybrids: Early dahlias had single rows of petals. Today, dahlias come in 20 flower forms in every color but blue (although hybridizers are working on that too). The simplest flowers ― single, semidouble, anemone, and collarette ― have one or two rows of petals (actually ray florets) surrounding a center disc, much like daisies. Ball and pompon dahlias are made up of multiple layers of tightly arranged petals, while cactus dahlias have layers of long, pointed, tubular petals.
There are also waterlily-shaped dahlias, peony-shaped dahlias, ones with fringed petals, and more. Flowers range in size from 2-inch-wide blooms to as big as dinner plates.
Sunset climate zones 1-24.
How to choose: Decide on varieties based on flower color, shape, and size. Keep in mind that large-flowered dahlias produce fewer flowers than small types.
Dahlias turn their brightly colored faces toward the sun, so site plants where you can see the blooms. Use tall ones in the back of the border and support with 5-to 6-foot long stakes; use dwarf dahlias in the front of beds.
How to cut: Snip flowers often to keep plants producing. Cut blooms early or late in the day, selecting ones that have just opened.
Some growers suggest soaking cut ends in 160° to 180° water and allowing to cool for at least an hour before arranging.
Display in a cool spot and change water daily.
What dahlias need
Set tubers in the ground when the soil has warmed to about 60°.
Planting: Plant in full sun (afternoon shade in hot climates) and well-drained soil; mix in organic matter. Dig holes 1 foot deep and 1 to 1½ feet wide, and space tubers 1 to 5 feet apart, depending on plant size.
Lay tubers horizontally with growth buds facing up; cover with several inches of soil and water only if the soil is dry. Gradually fill in the hole as shoots grow.
Fertilizing: Mix ¼ cup low-nitrogen fertilizer into the bottom of the planting hole.
Watering: Once shoots appear, water regularly.
Pinching: Snip off growing tips when plants have their third set of leaves.
Winter care: In wet or cold climates, dig up tubers in fall.