Dahlia is a genus of bushy, tuberous, herbaceous perennial plants native to Mexico. It is a member of the Asteraceae (or Compositae) plants, and is a relative of the sunflower, daisy, chrysanthemum, and zinnia. There are some 50 species of dahlia, with hybrids commonly grown as garden plants.
Flower forms of Dalia are very variable. They can be as small as 2 inches, or up to 1 foot in diameter. This great variety results from dahlias’s unique chromosome structure compares to many other flower species. Formal coding systems have been developed for the expressed purpose to classify the multitude of varied forms of Dalia. Coding systems divide Dalia flowers into classes, each of which offers a full range of colors, heights, and bloom types. Codes are utilized most often in dahlia catalogs and at the many dahlia shows held all over the world.
In the Garden
With a multitude of different colors, shapes and sizes, Dahlias bring life and beauty back to landscape in late summer and into the fall months. The diversity of the Dahlia allow them to be used in many different aspects of landscape design, from low growing border plants to stately background plantings that may reach six feet in height. At the same time, the diversity also make it important to choose a form that matches the the intended garden style.
For tall-growing varieties, drive a 6-foot stake into the ground about 3 inches away from the tuber or roots. As the plant grows, tie the stem gently to the stake. Smaller varieties that grow to 2.5 feet or less do not require staking.
Dahlias also make excellent cut flowers, which will typically last about a week in the house.
- Bloom from midsummer to first frost
- Attracts butterflies and hummingbirds.
Dahliettas (Dahlia pinnata “Dahlietta”) are compact hybrid dahlias. They have smaller forms than traditional dahlias, but still retain the wide range of colors and shapes as their full-sized counterparts. Dahliettas are tender perenials but most often grown as annuals.
Caring & Growing
Generally winter hardy to USDA Zones 7-10, Dahlias thrive in the cool, moist climates of the Pacific Coast. Modestly suited to regions with extremely hot and humid climates, such as much of Texas and Florida.
Best flowering occurs in full sun, but plants generally appreciate some light, filtered shade in hot summer climates.
Dahlias tolerate most soil types, but prefer a sandy, well drained and slightly acidic soil. For heavy soil or clay, lighten the soil with sand and peat moss during planting.
Dahlias prefer consistently moist soil condition that is not saturated with water. Do not let the soil go dry while at the same time, avoid overwatering. After the plants are established, a deep watering 2-3 times a week for at least 30 minutes with a sprinkler, more required during warmer dryer weather, when rainfall is less than 1 inch per week. Water more often as conditions require, especially during growing season. Mulch can be added to the bed to help conserve moisture. Container-grown Dahlias require more frequent watering once plants are 12” high.
Dahlias require a low nitrogen fertilizer, such as used for vegetables. Use fertilizer with high percentage potassium and phosphorus fertilizers (such as a 5-10-10, 10-20-20, or 0-20-20) for better blooming. First applications should be within 30 days of planting and repeated again approx. 3-4 weeks later. Avoid high nitrogen compost and high nitrogen water soluble types as they promote weak stems, small blooms, or no blooms, and tubers that rot or shrivel in storage.
Misc. Maintenance Tips
To promote shorter, bushier plants with better stems for cutting, pinch or cut the center shoot just above the third set of leaves, or plant height of about 18-20” tall.