Delphinium grandiflorum 'Diamonds Blue'

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Herbaceous Perennial
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A compact, upright, clump-forming herbaceous perennial to 60cm in height, with green divided foliage. Strong, upright stems produce dense spires of cobalt-blue flowers with purplish blotches from June to August

Position

Full sun

Soil Types

Chalk, Loam, Sand

Max Height

0.5-1 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
2–5 years
Max Spread
0.1-0.5 metres
Max Height
0.5-1 metres

Growing Conditions

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

Position

Full sun
Aspect
East–facing or 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)
H5

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Ranunculaceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Clump forming, Columnar upright
Potentially harmful
Humans/Pets: Harmful if eaten. Wear gloves and other protective equipment when handling. For further information and contact numbers regarding pets, see the HTA guide to potentially harmful plants
Genus
Delphinium can be annuals, biennials or perennials, with palmately lobed basal leaves and showy bowl-shaped flowers in spikes, racemes or panicles
Name Status
Unresolved

How to Grow

Cultivation

Grow in fertile, well-drained soil in full sun. Shelter from strong winds and provide support (see staking perennials). Divide every 2-5 years to maintain vigour. See staking perennials and delphinium cultivation for further advice

Propagation

Propagate by division or by basal softwood cuttings in spring

Suggested planting locations and garden types

  • Cottage and informal garden
  • Cut flowers
  • Flower borders and beds
  • Wall side borders

Pruning

deadhead main stem after flowering to encourage side shoots to flower. Cut back to ground level in autumn

Pests

May be susceptible to aphids, slugs, snails, leaf miners and caterpillars, including swift moth caterpillar

Diseases

May be susceptible to delphinium black blotch, grey moulds, crown rot (on mature plants) and occasionally Cucumber mosaic virus. Powdery mildews may be a problem in periods of drought and on sites with poor air flow