Garden Dahlia

Overview

Dahlia pinnata is native to Mexico. It is the national flower of the country. The plant is sometimes harvested from the wild for local use as a food and dye. It is one of the parents of the cultivated Dahlias that are so commonly grown as ornamentals. The flower petals are used in salads. The root is cooked and used as a vegetable. A sweet extract of the tuber, called 'dacopa', is used as a beverage or as a flavouring. It is mixed with hot or cold water and sprinkled on ice cream. Its naturally sweet mellow taste is said to combine the characteristics of coffee, tea and chocolate. The root is rich in the starch inulin. Whilst not absorbed by the body, this starch can be converted into fructose, a sweetening substance suitable for diabetics to use.

Vernacular Names

Dahlia des jardins (French), Dahlie (German), Georgina pruinosa (Italian), Da li hua (Chinese),Tenjikubotan (Japanese), Dalria (Korean), Lajure Phool (Nepalese).

Agroecology

Found in rich damp oak and pine woods at elevations around 1,800 metres. The growing plant is very frost-tender, though the tubers are somewhat hardier tolerating temperatures down to about -5 °C. An easily grown plant so long as the soil does not dry out. It requires a deep rich soil with a pH 6-8, and a sunny position. It cannot grow in the shade. 

Morphology

• Root - large subterraneous tuberous. 
• Stems - hollow, leafy and branced.
• Leaves - opposite, simple, glaucous and glabrous beneath, ovate serrated leaflets, up to 10 cm long leaflets.
• Flower - hermaphrodite (has both male and female organs), inflorescence is solitary, involucrate, long pedunculate and 10 to 20 cm across. Disc florets are actinomorphic, bisexual, tubular and five lobed. Ray florets are zygomorphic, several marginal rows, pink to deep purple in colour.
• Fruit - an achene which is dorsally compressed with pappus being absent or shortly bidentate.

Cultivation

• Generative propagation is by seed - usually germinates in 1-3 weeks at 20 °C. When they are large enough to handle, prick the seedlings out into individual pots and grow them on until large enough to plant out.
• Vegetative propagation is by cuttings and division. Cutting of young shoots as new growth begins, and division of the tubers when dormant. Each portion should have a growing point.

Chemical Constituents

Essential oils (D-limonene, 4-terpineol and α-terpineol), flavonoids (antocyanin, butein, and flavon), and inulin.

Traditional Medicinal Uses

• In Pre-Spanish Mexico, tubers were used for diabetics.
• Petals and tubers were used by Aztecs for treating infected grazes, rashes and cracks in skin, and used the flowers to treat epilepsy.
• The crushed and mashed up petals are used to provide relief from stings or insect bites.