All About Dahlias

Big or small, dahlias steal the show


Of the various late summer and fall flowers, dahlias occupy a place near many gardeners´ hearts. The range of types, sizes, and colors are spectacular. They range from small pompom blooms to amazing, oversized "dinner plate" flowers in vivid colors. Many aficionados consider the dahlia to be the "flower of flowers."


Dahlias originated in Central America and are native from Mexico to Costa Rica. The flowers were known to the Toltecs. An Aztec herbal written in Latin in about 1550 was rediscovered in 1929 and in it, evidence of the dahlia´s use as a treatment for epilepsy.

Plants were taken back to Europe by Spanish adventurers more than 200 years ago. At the Botanical Gardens in Madrid, the Abbe Cavanille named the genus "Dahlia" for Andreas Dahl, a noted Swedish botanist and student of Carl Linnaeus.

There are currently 35 recognized species. The first species were Dahlia pinnata, D. rosea, and D. coccinea. Because the dahlia is a natural hybrid, developing new varieties from the original simple blooms to a vast range of single and double-flowered blossoms in saturated bright colors and a multitude of shapes has been relatively easy.

During the 1800s the popularity of dahlias surged; thousands of varieties emerged and were documented. After a brief flirtation with using dahlia tubers as a food crop to supplement potatoes, it was decided that it was better suited to decoration than food. The rounded pompom was developed in Germany around 1850 and cactus-type emerged from a bit of tuber cultivated in Holland during the 1870s.

The popularity of dahlias continues to grow. They are easy to cultivate, beautiful, and readily available.

Growing Dahlias

Former owner of Log Cabin Dahlias in Hillsboro, Oregon, Katie Unger offers the following advice for cultivating dahlias:

PLANTING—Full sun is the ideal location for most dahlias. The exception is hot climates. In these areas it is best to select a spot with morning sunlight, but not the hot afternoon sun. Dahlias are usually planted about the same time as vegetable gardens. Delay planting until all danger of frost is over and soils have warmed up. For most climates, this is Mid-April through May. In warmer, southern states dahlias can be planted in March. A well-drained deep soil works the best. Lay tubers flat with the eye pointed up. Plant 3-6 inches deep 18-24 inches apart. Bone Meal or a low nitrogen fertilizer such as 5-10-10 can be added at planting time. Too much nitrogen can cause excessive vegetative growth and fewer blooms. Do not use bark dust on dahlia beds. For container gardening, we suggest garden soil or a mixture of garden and potting soil.

The shoots take 2-4 weeks to emerge. Slugs and snails can be a major problem. We recommend putting slug bait out at planting time and follow up as needed. Taller varieties of dahlias will need to be staked. To avoid damaging the tubers, stake before or at planting. The moisture in the spring soil is sufficient to promote growth. Do not water the tubers at planting time. Over watering early in the season can rot the tubers.

SUMMER CARE—Once the weather has warmed up and the top growth has emerged, you can begin to water. A deep watering weekly should be adequate. When your dahlia plants are 12-20 inches tall with no more than 4 sets of leaves, cut or pinch the center shoot. This produces shorter, bushier plants with more flowers. Removal of old blossoms promotes more blooms and keeps the plant growing vigorously.

It is best to cut flowers for bouquets early in the morning or late in the evening. To set the blooms for longer lasting enjoyment, put the stems in 2-3 inches of very hot water (about 160 degrees) and allow to cool for one to two hours. Aphids, cucumber beetles, earwigs and gophers can be a problem during the growing season. Check your garden store for control of these pests.

FALL CARE—In cold climates it is best to dig and store the tubers for winter. Freezing temperatures and excessive moisture can cause rot. In mild climates, dahlias can be left in the ground to re-grow the next season if they are protected from frost.

Dig tubers two weeks after the first frost or wait until the middle of November. Wash clumps and let them dry (not in hot sun). Clumps can be divided before storage or in the spring. Protect from freezing. A storage area about 40-50 degrees is ideal. Tubers or clumps can be placed in vermiculite, sawdust, or peat moss to prevent shriveling. A tuber needs to have an eye for it to produce a plant. The eyes are located next to the stem. They may be easier to see in the spring.

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