Dahlia 'Cornwall Island' (Fim)

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dahlia 'Cornwall Island'

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dahlia 'Cornwall Island' RHS
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Bedding Herbaceous Perennial

A bushy, clump-forming, tuberous perennial to around 100cm in height, with dark green serrated leaves. Dark pink to purple flowers with recurved petals, split at the ends, give a 'starburst' effect and appear from summer through until the first frosts

Position

Full sun

Soil Types

Clay, Loam, Sand

Max Height

0.5-1 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
1–2 years
Max Spread
0.1-0.5 metres
Max Height
0.5-1 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)
H4

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Asteraceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Bushy, 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
Accepted
Horticultural Group

Horticultural Classification Codes

Horticultural Classification Codes are often given to genera which have a large number of species or cultivars. They are used to categorise cultivated plants based on specific, shared characteristics such as shape, colour, size or flowering time, and can be displayed as letters or numbers

For example:
Dahlia ‘Sunset Kate (Sin) = Single flower
Rosa ‘Marigold’ (HT) = Hybrid Tea

Fimbriated dahlias have splits in the tips of the florets and no visible central disc, giving them a soft, feathery texture

How to Grow

Cultivation

Grow in fertile, humus-rich, well-drained soil enriched with organic matter, in full sun. Pinch out growing tips to encourage bushy plants and stake - see staking perennials. Water if needed 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 This plant was included in the RHS Dahlia trial 2023-2024 https://www.rhs.org.uk/plants/trials-awards/plant-trial-results/dahlia

Propagation

Propagate by softwood cuttings taken in spring from shoots from stored tubers, or divide the tubers ensuring each division has a viable bud

Suggested planting locations and garden types

  • City and courtyard gardens
  • Cottage and informal garden
  • Patio and container plants
  • Bedding
  • Cut flowers
  • Flower borders and beds
  • Wall side borders

Pruning

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

Pests

May be susceptible to aphids, leaf miners, glasshouse red spider mite and slugs. Earwigs sometimes damage blooms. Capsid bug and caterpillars are occasional pests

Diseases

May be susceptible to powdery mildews in dry conditions. In wet weather grey moulds and other fungal rots can be a problem. Fungal rots can also damage stored tubers. A virus may cause stunting, leaf markings and distortion