Dahlia

Asteraceae

Dahlia

There are  dwarf types up to 15cm and tall types up to 2.5 metres, and a large variety of flower types. Flowers are borne as one head per stem and range from 5cm to 30cm across, and may be single or double. Colours range from creams through yellows, oranges, reds and pinks. The mid-green pinnate leaves are produced on the same stems as the flowers. A few varieties have bronze foliage. 
 

Uses

Garden borders, shrubberies, and cut flowers. Annual species grown from seeds make good bedding plants. 
 

Culture

These tuberous plants require full sun. They are frost-tender and can be planted any time after frosts till the end of summer. The ideal pH is 6 7. Plants are wind-sensitive and should be irrigated well (suffers from being too dry). To get exhibition type blooms, remove side shoots on developing flowers and allow only one flower to a stem, pick flowers early in the morning and dip the base of the stem in boiling water as soon as picked since this improves their keeping quality.  Lift the tubers a month or two after the flowering stops.
 

Propagation

They are best propagated from division of offsets. Basal cuttings also work but take longer to flower and need bottom heat. The border species do not grow true to type form seed though bedding species are invariably grown from seed.  
 

Cultivars

A very large number of named cultivars are grown, including:

D. 'Bridesmaid' - an anemone-flowered dahlia to 1.3m. These have double flowers with flattened white outer florets surrounding shorter yellow tube-shaped florets.    

D. 'Can-Can' - a collerette dahlia to 1.3m. These have flat flowers to 12cm with an outer ring of pink petals and an inner ring or collar of smaller yellow florets.

D. 'Holland Festival' - a giant decorative dahlia to 1.6m. These have fully double flowers with broad flattened and pointed ray florets which are deep orange with white tips. 

 

Plant Health

They are prone to cucumber mosaic virus and tomato spotted wilt both of which cause stunted or distorted growth. Flowers and stalks may become infected with petal blight, grey mould and sclerotinia. Verticillium wilt  can also be a problem. Cuttings may be affected by damping off.  Aphids, earwigs, caterpillars and capsid bugs may damage above ground parts.
 

More info

There are more than 30 species of this genus mostly from Mexico but also central America and northern parts of South America. 

 

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