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Delightful Dahlias

by Dr. Leonard Perry, Extension Professor,University of Vermont    

We have the Aztecs to thank for the dahlia, a summer bulb that brightens up the late-season garden.

Dahlias range in color from white and yellow to orange, pale pink, lavender, and red with blooms from half an inch to a foot and a half in size. Flowers may be pompoms or pinwheels with single or double petals that are flat, curved, or rolled into tubes. A long-lasting cut flower, it makes a great addition to any garden.

The dahlia, a relative of the daisy, was first cultivated by Aztec botanists in Mexico. In the early 1500s it was discovered by Spanish explorers who brought this tuberous plant back to Europe. Interestingly, they had the same problem with storage of the tubers as do many modern-day gardeners. The genus Dahlia gets its name from an 18^th-century Swedish botanist, Andreas Dahl.

The dahlia became a favorite in the gardens of working class Europeans after being distained by the upper class as being too flamboyant for their carefully manicured gardens. However, it gained prominence in the mid-1800s after a devastating blight wiped out the potato crop in France as it was thought to be a good substitute for this starchy vegetable. Unfortunately, it was not, but it soon became popular in gardens both for its flowers and interesting foliage.

Although a perennial plant, in northern climates dahlias are treated as annuals. They are planted in the spring as soon as the soil has warmed up, then lifted and stored in the fall after the first hard frost.

Dahlias do best in a sunny spot with light, fertile, well-drained soil. If you have heavy clay soil, work in a two- to four-inch layer of well-rotted manure or compost a few weeks before planting. Add fertilizer--about a quarter pound of a balanced fertilizer like 5-10-5 per ten square feet of garden or according to soil test results--incorporating it into the soil well. With a slow release, complete fertilizer no further applications are needed.

Wait until the danger of frost has past before planting the tubers. Plant about four to six inches deep, laying them horizontally on their sides, with roots down and buds facing upward. Cover with two inches of soil, adding more as shoots appear.

Space smaller varieties two to three feet apart, larger ones three to four feet. Larger plants also will require support as they grow. To avoid damage to the roots later on, drive a stake into the ground now, a few inches from where you plan to plant each tuber. As the plants grow, tie the stalks to the stakes.

Most dahlias will bloom in late summer and early fall. Some of the newer and bedding varieties are relatively short, a foot or so high, and generally bloom repeatedly through season. Pinch off spent blooms to encourage continual flowering. Once frost has blackened the foliage, it's time to dig them up and store until the following spring.

With a sharp knife, cut the stalks at a height of about a foot. Then carefully dig up the clumps, taking care not to injure or spear the tubers. Trim the stalks to a few inches. Shake off the loose dirt and separate the tubers, allowing them to dry for a few days.

Brush off the remaining dirt, then place in a shallow box containing sand and peat moss. Label and store in a dry, cool place. The ideal storage temperature is 40 degrees F.

Throughout the fall and winter check the stored tubers regularly for signs of rot or mold. Spray soft or shriveled tubers with warm water, then let dry before returning to storage. Bruised or rotted tubers will need to be discarded.


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University of Vermont