Dahlia imperialis - Giant Dahlia

The Dahlia Imperialis is the giant of the genus, with its tree-like habit that can reach a height of 4 metres (13 feet) under good conditions. This botanical species impresses with its bamboo-like appearance and lush growth and charms with its beautiful autumn flowering when not destroyed by frost or wind. At the top of this lovely plant, large panicles of flowers in wide and unpretentious heads bloom, which can be admired from below: around a beautiful yellow-orange centre, pretty pale pink scarves are arranged, slightly crumpled.

The Dahlia imperialis belongs to the large botanical family of Asteraceae, just like our garden dahlias. It is native to Central America's high plateaus and mountains, from Mexico to Guatemala, where it is found at altitudes between 1500 and 1700 m (4921 and 5577ft). It is a herbaceous plant with semi-woody stems, perennial due to its large tuber and artichoke-like taste. Its cold resistance is quite limited; its roots are destroyed below -5°C. With a thick protective mulch planted in a warm and dry location, this dahlia will survive short periods of freezing temperatures around -8°C.

Depending on the region, this tree-like dahlia starts late in spring, more or less early. But its rapid growth can reach 2 to 4 m (7 to 13ft) in height with a spread of 1 to 1.50 m (3 to 5ft) in a few months. From the ground emerge powerful, hollow, and green-coloured herbaceous stems with a circumference of 8 to 10 cm (3 to 4in). Prominent rings, similar to bamboo canes, mark them. Each stem branches out. It bears large leaves divided into seven ovate and dentate leaflets, carried by purple petioles. Their colour is deep green on the upper side and more glaucous on the lower side. A decrease in day length induces flowering. It usually occurs in October-November or even as early as September, depending on the climate. At the tips of the stems, 30 to 35 flowers bloom, organized in heads on a mature plant. Each head measures 10 to 13 cm (4 to 5in) in diameter. Slightly inclined, somewhat campanulate, and not fully open, their style resembles single-flowered decorative dahlias. The central disk of the head is composed of tiny florets in yellow-orange colour. It is surrounded by a collar of ligules, or slightly crumpled 'petals', in pale lavender pink. The first frost will destroy the above-ground vegetation of this dahlia. The plant goes dormant underground in winter.

Extremely decorative, this captivating plant will find its place in a sheltered position from wind and cold, warm and sunny. The Dahlia imperialis deserves a prime location in the garden: in front of a screen of bushes that will cut the wind, near the house's entrance against a protective wall, or even in the corner formed by two facades. It can be associated with plants with exotic charm, such as banana trees or palm trees, giant cannas, or castor oil plants. In a romantic setting, its flowering will accompany late-flowering shrubs, such as Aralia elata, strawberry trees, or autumn camellias.