Dahlia imperialis White - Giant Dahlia

Dahlia imperialis 'White' is rarer than the usual species with pink flowers. It is also slightly less vigorous, but is just as wonderful. This tree-like plant charms with its bamboo-like appearance, lush foliage, and beautiful autumn flowering. However, it is sensitive to cold and wind. It bears panicles of flowers in large, simple, and unpretentious heads, which can be admired from below.

Dahlia imperialis 'White' belongs to the large Asteraceae family, just like our garden dahlias. Its wild ancestor is native to the high plateaus and mountains of Central America, from Mexico to Guatemala, where it is found at altitudes between 1500 and 1700m (4921 and 5577ft). It is an herbaceous plant with semi-woody stems, perennial thanks to its large edible tuber with an artichoke-like taste. Its cold resistance is quite limited. Its stump is destroyed below -5°C (23°F). This dahlia will, however, be able to survive short periods of frost at around -8°C (17.6°F) if the plant is protected with thick mulch and planted in a warm and dry location.

This tree-like dahlia starts quite late in spring, depending on the region. Its growth rate is rapid and it can reach 2 to 3m (7 to 10ft) in height and 1 to 1.25m (3 to 4ft) in width in just a few months. Powerful, hollow, green-coloured herbaceous stems emerge from the ground. They have a circumference of up to 6 to 8cm (2 to 3in). They are marked by prominent rings, like bamboo canes. Each stem shoots up and branches out. It bears large leaves divided into 7 ovate, toothed leaflets, carried by purple petioles. Their colour is a deep green on the upper side, more glaucous underneath. The flowering is induced by the shortening of the day length. It usually occurs in October-November, or even as early as September (depending on the climate). At the top of the stems, inflorescences composed of 30 to 35 flowers are arranged in heads on an adult plant. Each head measures 10 to 12cm (4 to 5in) in diameter. They are slightly inclined, somewhat campanulate, and not fully open. Their style somewhat resembles single-flowered decorative dahlias. The central disk of the head is composed of tiny yellow-orange florets. It is surrounded by a white collar of ligules or 'petals' that are somewhat crumpled. The above-ground vegetation will be destroyed by the first frosts. The plant goes into dormancy underground in winter.

It is an extremely decorative plant that should be planted in a warm and sunny position, sheltered from wind and cold. Dahlia imperialis 'White' deserves a prime location in the garden. Place it in front of a screen of bushes that will cut the wind, near the entrance of the house against a wall that will protect it, or even in a corner formed by two facades. It can be combined with exotic plants, such as banana trees, palm trees, giant cannas, or even castor oil plants. In a romantic setting, its flowers will complement autumn-flowering shrubs, such as Aralia elata, Arbutus unedo (strawberry tree), or even autumn camellias.