Dahlias: now is the time to plan for these vivid, varied and versatile summer showoffs - includes sources

Flower & Garden Magazine, April-May, 1994 by Jerry Gabrielse

Few flowers have the power to dazzle like dahlias. From its humble Mexican and Central American beginnings, the dahlia has become one of the grandest of flowers, capable of creating a royal presence in any garden.

The flower's Aztec names, cocoxohit and acocotli, allude to the dahlia's hollow stems and their use by the Aztecs as water pipes. Modern tongues have an easier time pronouncing dahlia, a name chosen to honor the 18th-century Swedish botanist Andreas Dahl.

The first dahlias to arrive in Spain from Mexico, late in the 18th century, were tall, gangly plants with open-centered red flowers. Hybridizers in England, France and the Netherlands discovered the incredible diversity of the dahlia, producing new varieties in a vast array of floral shapes, sizes and colors. Today we can grow and enjoy dahlias of many kinds in our backyard gardens.

One wonderful characteristic of the dahlia is its versatility. Dwarf varieties stay small and work great for patio pots or low borders. Intermediate heights, from 2 to 3 feet, work as seasonal hedges or closely spaced mass plantings. The giants reach 5 to 7 feet tall and are suitable for backdrops; these taller plants need support to remain upright.

Another factor in a dahlia's appeal is its variation in blossom shapes and styles. Ball, cactus, anemone, pompon, formal decorative and peony-flowered are just a few of the more commonly recognized profiles. Almost every flower color except clear blue is represented, making it possible to include dahlias in any color scheme. And for gardeners who like their flowers big, the dahlia is one that can live up to the descriptive label of "dinner plate."

Although they're often grouped with caladiums and gladioli as "summer bulbs," dahlias actually grow from tuberous roots. Their blooming season in most climates is from mid-summer until frost - a longer period than most other summer bulbs. During this lengthy show, the more you cut the blossoms for cut flowers, the more prolific they become. It is not unusual for one plant to produce 50 to 100 flowers in just one season. What a harvest!

The dahlia's requirements are minimal and not at all out-of-the-ordinary. Although they accept most any garden soil, dahlias are grateful for a soil rich in organic matter, phosphorus and potash.

Dahlias grow best in full sun, but some shade during the hottest part of the day helps to prolong the blooms. The flowers tend to face their greatest light source, a characteristic to consider when choosing their placement. Plant your dahlias so that when the blossoms face the sun they are also facing the path, patio or window from which you will view them.

Plant dahlias in spring, when frost no longer threatens and the soil has warmed. A few weeks before planting time, remove dahlia clumps from storage and divide them. Cut the roots apart, making sure each division has one of the white growth eyes, or buds, located at the base of the previous year's stems. Undivided clumps can also be planted, creating a lusher, bushier plant, but flower size will be reduced.

Dust the cuts with garden sulfur or a fungicide, then place the roots in damp sand or compost indoors to encourage sprouting. This step gives the dahlias a running start on the season, but is not mandatory. You could also plant roots directly from storage into the garden.

As soon as weather allows, plant the roots outdoors in prepared soil. Dig holes one foot deep and about as wide. mix one-quarter cup of 0-20-20 fertilizer in the soil at the bottom of the hole. Fill the hole halfway with soil. Place the root division horizontally with the eye or sprout facing upward. Cover the root with 2 or 3 inches of soil (not all the way to the top of the planting hole). Water well. Drive sturdy stakes alongside the roots of tall dahlia varieties that will need support; stakes installed later, after the plants are growing, could damage the roots.

As the young shoots grow, gently fill the planting hole with soil. If full, bushy plants and abundant blooms are what you most enjoy, pinch back the first shoots above the third or fourth pair of leaves. An early pinch encourages branching and only briefly delays the first blooms.

Dahlias like moisture, especially during their growth period. After shoots emerge, water them often to a soil depth of about one foot. Mulch with wood chips, pine needles or other organic material to conserve moisture and eliminate the need for surface cultivation.

Several techniques are often suggested for extending the life of cut dahlias. Dipping the stem ends in boiling water or searing them with a candle flame are two. Another method is to cut the flowers early in the morning and immediately immerse 2 inches of the stems in hot water; leave them in a cool spot for several hours before arranging them.

When the first frost lays down its soft but deadly blanket, dahlia foliage blackens. Immediately dig the roots, which likely will have multiplied during the summer. Dry them in the sun for a few hours before storing them in plastic-lined boxes or other containers filled with dry peat moss, sand or vermiculite. I have had good luck storing dahlia roots in buckets of dry garden loam. Keep the roots cool (a constant temperature of 40 to 45 degrees is ideal) in a well-ventilated, dark space until spring. It's wise to check the condition of stored dahlia roots every month or so; lightly moisten the storage medium if the roots show signs of shriveling.