Dahlias are half hardy, so keep them protected from frost. Pot tubers individually between February and April and grow them on in a greenhouse or bright indoor position. Alternatively, start them outside in May, once the risk of frost has passed.
Out of season
Deluxe
The impressive Dahlia imperialis reaches heights often in excess of 250cm—in a single season! In their native environment (Mexico, Central America and Colombia), they can even grow to 8-10 metres tall. For this reason, it goes by several common names, including bell tree dahlia, giant dahlia or just tree dahlia. Its long, thick, bamboo-like stems are clothed in large, elder-like, fresh green leaves, making it a fine and splendid foliage plant. To ensure flowering, it needs to be grown in a frost-free situation. A warm autumn is when you are most likely to get the best flowering. When they come, the single blooms are of a gorgeous soft pink-purple, with orange centres.
Grow Dahlia imperialis in a moist but well-drained soil, in a sheltered spot in full sun. It is an ideal dahlia for a tropical border in the garden, or you can grow it in a large greenhouse or conservatory, where its chances of flowering are greatly increased. Its stems are so sturdy, there is usually no need to stake. As with all dahlias, lift the tubers of the bell tree dahlias and store them frost-free over winter.
Quantity
Plant profile
Plant calendar
For planting out later, use a snug-fitting 15–20cm pot filled with peat-free multipurpose compost. For a patio display, plant directly into a container at least 30cm wide and keep it somewhere bright and frost free until it can move outdoors.
Position the old stem facing upwards, with the tubers covered and the stem stump level with the compost. Tubers naturally vary in size and shape and may arrive without visible buds. Bent necks are usually fine if they remain firmly attached, so do not remove them.
Water after planting, then allow the compost to become almost dry before watering again while the tuber remains dormant. Once shoots and leaves are growing strongly, water more regularly, always allowing excess water to drain away.
Plant out after the last frost, once the plant is around 20–30cm tall and its roots hold the compost together. Space dahlias approximately 30–50cm apart in borders, allowing less room for compact varieties. Water thoroughly after planting.
Water regularly during active growth and deadhead or cut flowers often. Dahlias usually bloom from July or August until the first frost, although later-planted tubers may start in late August or September. In autumn, lift, clean and dry the tubers, then store them somewhere cool, dry, airy and frost free.
- Botanical name
- Dahlia imperialis
- Flower colour
- Pink, purple
- Tuber size
- 1
- Established height
- 2.5-3m
- Established spread
- 1-1.2m
- Growing skill
- Easy to grow
- Habit
- Upright
- Hardiness
- Half hardy
- Leaf colour
- Green
- Mouse resistant
- No
- Plant spacing
- 1 tuber per m2
- Pollinator friendly
- No
- Position
- Sheltered
- Rabbit resistant
- No
- Scented
- No
- Soil acidity
- Any
- Soil moisture
- Free draining
- Soil type
-
Loam
Sandy
Multipurpose compost
Loam-based compost - Suitable for
-
Borders
Cottage gardens
Low maintenance gardens - Sunlight
-
Full sun
Partial shade - Toxicity
- No report
- Years to establish
- 1st year
Good for cutting
Thrives in full sun
Perennial
Packed in paper
Low maintenance
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Dahlia imperialis reviews
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