Plant Type:
Herbaceous perennial
The ornamental beauty of Dahlia imperialis lies in its towering, bamboo-like stems and lush foliage, creating a dramatic, tropical effect. Occasionally, it graces with nodding, mauve-pink flowers. Originating in the uplands of Mexico and Guatemala, this “tree Dahlia” brings an exotic grandeur to gardens.
Cold Hardiness:
Half hardy
Dahlia imperialis is frost-hardy at the root zone in the UK. It is generally considered hardy down to around -5°C, which corresponds to RHS hardiness zone H3. Therefore, in s0me UK gardens, the tubers will need winter protection to survive temperatures below this.
Eventual Height:
2.5-4m
Dahlia imperialis is a truly statuesque plant, capable of reaching impressive heights in a single growing season. In the UK, expect its bamboo-like stems to soar to between 2.5 and 4 metres (approximately 8 to 13 feet) under favourable conditions, creating a dramatic vertical element in your tropical garden.
Light requirements:
Partial shade / Full Sun
Dahlia imperialis thrives in a sunny spot, requiring at least 6-8 hours of direct sunlight daily to encourage strong growth and the best chance of its late-season flowers. While it can tolerate some partial shade, especially in the hottest part of the day, too much shade will result in leggy growth and reduced flowering. Choose a sheltered location to protect its tall stems from strong winds.
Water Requirements:
Average
Dahlia imperialis needs consistent moisture, especially during its rapid growth in warmer months. Water deeply 1-2 times a week, allowing the soil to dry slightly between waterings to prevent root rot. Avoid waterlogging. During dry spells, increase watering frequency. Water at the base to keep foliage dry and reduce disease risk. Potted plants will need more frequent watering.
