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
Dahlia imperialis
'Alba'
white bell tree dahlia
If you're looking for something structural, exotic and exciting to grow, you must give Dahlia imperialis 'Alba' a try. Unlike the familiar blousy dahlias which are commonly seen flowering through summer, this tree-like version (also known as bell tree dahlia) is truly something else. Native to Mexico and Central America, it's better adapted to cope with heat. In a warm climate, this white variety can grow up to 8m tall with woody, bamboo-like stems! In a cooler climate, Dahlia imperialis 'Alba' typically reaches a less daunting size of 2.5m and will die back for winter, as with most dahlias. This architectural plant has fantastic foliage through the summer season and, if it's a long, hot summer, it'll treat you to an extra special, late-season display of starry white blooms in October.
Dahlia imperialis 'Alba' is not frost hardy so you will need to plant the tubers in frost-free conditions in spring and plant outside after risk of frost has passed. After the first frost in autumn, it'll be necessary lift and store the tubers for winter in areas where winter temperatures fall below zero. This white bell tree dahlia needs a moist but well-drained soil and a sunny spot in the garden. You can increase its chances of flowering in autumn by growing it in a conservatory or heated greenhouse in spring, which will get it off to a speedy start!
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 'Alba' (Sin)
- Flower colour
- White
- 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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