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Dahlia
Dahlia is a genus of bushy, tuberous, perennial plants native to Mexico, Central America, and Colombia. There at least 36 species of Dahlia. Dahlia hybrids are commonly grown as garden plants. The Aztecs gathered and cultivated the dahlia for food, ceremony, as well as decorative purposes [1], and the long woody stem of one variety was used for small pipes.
In 1872 a box of Dahlia roots were sent from Mexico to the Netherlands. Only one plant survived the trip, but produced spectacular red flowers with pointed petals. Nurserymen in Europe bred from this plant, which was named Dahlia juarezii with parents of Dahlias discovered earlier and these are the progenitors of all modern Dahlia hybrids. Ever since, plant breeders have been breeding Dahlias to produce thousands of cultivars, usually chosen for their stunning and brightly coloured flowers. Dahlia plants range in height from as low as 12" (30cm) to as tall as 6-8 feet (180-240cm). The flowers can be as small as 2" (5 cm) or up to a foot (30 cm) in diameter. The great variety results from Dahlias being octoploids (they have eight sets of homologous chromosomes, whereas most plants have only two).
Dahlias are used as food plants by the larvae of some Lepidoptera species including Angle Shades, Common Swift, Ghost Moth and Large Yellow Underwing.
The dahlia is named after Swedish 18th-century botanist Anders Dahl. Until recently they were also named in Germany as "georgine" by the botanist Carl Ludwig Willdenow, after the naturalist Johann Gottlieb Georgi of St. Petersburg.
Scientific classification
Dahlias belong to the family Asteraceae (or Compositae). The dahlias introduced into cultivation probably belonged to the species Dahlia pinnata.Types
- CACTUS DAHLIAS
- HYBRID CACTUS OR SEMI-GAGTUS TYPE
- DECORATIVE DAHLIAS
- BALL-SHAPED DOUBLE DAHLIAS
- PEONY-FLOWERED OR "ART". DAHLIAS
- DUPLEX DAHLIAS
- SINGLE DAHLIAS
- COLLARETTE DAHLIAS
- ANEMONE-FLOWERED DAHLIAS
- MINIATURE OR POMPON CACTUS
- BEDDING DAHLIA
- COCKADE OF ZONAL DAHLIAS
When & Where to Plant
For best results, dahlias should be planted from mid April through May for most areas. Ground temperature approx. 60 degrees. (exceptions will be hot climates). In general about the same time you would plant your vegetable garden. Dahlias need a sunny location to thrive. An area that receives at least 8 hours of direct sunlight is best. Exception for hot climates, they will need morning sunlight, afternoon shade. Less sun equals taller plants and less blooms.Soil Preparation
Ground should be warm, well drained at planting, and in an open sunny location. If you have a heavier soil, add in sand, peat moss or bagged steer manure to lighten and loosen the soil texture for better drainage. Bone meal is ideal at planting time, put a small handful in the hole and work in well before planting tuber. PH level of your soil should be 6.5-7.0, slightly acidic. Do not amend dahlia beds with purchased top soils unless you are sure that it has not been treated in any way for weeds. Compost of any type should be avoided.Grow Dahlias
Lay the tuber horizontally 4-6” deep, about 18” to 24” apart, and then cover with soil. DO NOT WATER TUBERS AFTER PLANTING!! Please wait to water until after the sprouts have appeared above the ground. The exception will be in hot climates, where they should be watered very lightly. Do not use bark dust or mulch to cover dahlias, as it does not allow the soil to warm up or tubers to sprout properly. This is a good time to apply snail and slug bait to protect the new sprouts.Container Growing
We do not recommend growing dahlias in pots, but if you choose to, low growing or dwarf dahlias work best in containers. Container size should be no smaller than 12” x 12” per tuber. Use 2 parts garden soil, 1 part potting soil that has not been treated in any way. Water sparingly, overwatering to keep soil damp will result in rotting tubers in the pots. After plants are 12” high, potted dahlias will require extra watering and fertilizing to promote proper blooming.Staking
We recommend staking any dahlias that will reach 3 feet or taller. Any staking product will work, please check your local garden center - i.e.: tomato cages, metal rods, or bamboo stakes.Watering
Most areas have enough rain to fill dahlia water needs until the sprouts appear above the ground. After dahlias are established, a deep watering 2-3 times a week for at least 30 minutes with a sprinkler, more required during warmer dryer weather. Hotter climates will need to water more often as conditions require. Proper watering promotes proper blooming. Hand watering is not enough.Fertilizer
Dahlias require a low nitrogen fertilizer, such as used for vegetables. We recommend high percentage potassium and phosphorus fertilizers such as a 5-10-10, 10-20-20, or 0-20-20. First applications should be within 30 days of planting and repeated again approx. 3-4 weeks later. One of the biggest mistakes made with dahlias is over feeding them. Avoid 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.Topping or Pinching
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.Cut Flowers
When cutting dahlias, work in the morning while it is still cool and take a container of water to the garden with you. Immediately put the cut end under water for best long term freshness. For the best display, cut only flowers that are fully open. Some gardeners believe the cut dahlia flowers last better if the cut ends are dipped into very hot (not boiling) water; others simply plunge them into cool water. You could experiment and see what works best for you. I have never figured out how to get that hot water out to the garden! (Maybe a camping stove?)
The cut flowers will keep better if you remove the foliage that is under water and also use a commercial floral preservative in the water. As with any cut flower, keeping them at a cool room temperature and out of direct sun and out of drafts will also help them to last longer.