Dahlia imperialis (B)

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tree dahlia

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tree dahlia visionspictures.com

Other common names

giant dahlia, imperial dahlia

Herbaceous Perennial
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A wild, species dahlia with tuberous roots, growing up to 4m, with mid-green leaves divided into many leaflets with long pointed tips. Nodding, mauve-pink, cup-shaped flowers up to 10cm across have eight petals and a central yellow disc. However, it tends to bloom too late in the season to avoid frosts so is usually grown as a foliage plant

Position

Full sun

Soil Types

Clay, Loam, Sand

Max Height

2.5-4 metres

Max Spread

1-1.5 metres

Size

Time to Maturity
1 year
Max Spread
1-1.5 metres
Max Height
2.5-4 metres

Growing Conditions

Clay Loam Sand
Moisture
Moist but well–drained
pH
Acid or Alkaline or Neutral

Position

Full sun
Aspect
South–facing or West–facing
Exposure
Sheltered
Hardiness

Hardiness Ratings

All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

  • H1A: under glass all year (>15C)
  • H1B: can be grown outside in the summer (10 - 15)
  • H1C: can be grown outside in the summer (5 - 10)
  • H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
  • H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
  • H4: hardy through most of the UK (-10 to -5)
  • H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
  • H6: hardy in all of UK and northern Europe (-20 to -15)
  • H7: hardy in the severest European continental climates (< -20)
H3

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Asteraceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Clump forming
Genus
Dahlia are tuberous rooted perennials with pinnately divided leaves and showy flowerheads, double in many cultivars, in summer and autumn
Name Status
Correct
Plant Range
Mexico to Colombia

How to Grow

Cultivation

Grow in full sun, in fertile, humus-rich, well-drained soil enriched with organic matter and general-purpose fertiliser. Pinch out growing tips to encourage bushy plants. Water freely in dry periods. Lift and store tubers in autumn to replant, or use as a source of cuttings, in spring. See dahlia cultivation and our video How to plant dahlia tubers and care tips

Propagation

Propagate by softwood cuttings taken in spring from shoots from stored tubers, or divide the tubers, ensuring each section has at least one viable bud

Suggested planting locations and garden types

  • Cottage and informal garden
  • Flower borders and beds

Pruning

Deadhead to prolong flowering. Cut back to near ground level in autumn, once frost has damaged foliage, before lifting and storing for the winter

Pests

May be susceptible to aphids, capsid bugs, caterpillars, earwigs nibbling flowers, glasshouse red spider mite and slugs

Diseases

May be susceptible to powdery mildews in dry conditions, fungal rots including grey moulds in wet conditions and in storage, and a virus that causes stunting, leaf markings and distortion