Giant dahlia or tree dahlia, Dahlia imperialis, is an enormous species growing to 3m, bearing thick, bamboo-like stems and large, elder-like leaves. It makes a fantastic foliage plant in its own right, however, if grown in a sheltered spot in a mild region, it may bear single, pink-purple blooms with orange-centres, from late October onwards. It's a great choice for a tropical border but may also be grown in a large greenhouse or conservatory, where its chances of flowering are greatly increased.
Tree Dahlias are a magnificent, towering variety that blooms through to early winter before dying down completely.
Dahlias thrive in full sun to part shade and are ideal for pots and containers. They need around six hours of sun daily, with morning sun being ideal. They typically bloom 3-4 months after planting and can flower for months with regular deadheading. These plants are excellent for gardens, featuring long flowering periods, lush foliage, and a variety of colours, shapes, and sizes. Dahlia flowers are great for cutting and last well in vases. Cutting flowers in the morning and taking at least two leaves per stem encourages more blooms and bushy growth.
Plant your dahlias in moist, humus-rich, well-drained soil, and mix in well-rotted manure before planting. Plant tubers about 10 cm deep and stake tall varieties during planting to avoid root disturbance. Ensure good air circulation between plants. Dahlia tubers don't need to be lifted if the soil is well-drained and doesn't freeze. However, they should be dug up and divided every few years to maintain optimal flowering.