Hemerocallis 'Cerulean Star'

RHS Plant Profile
daylily 'Cerulean Star'

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Herbaceous Perennial

A deciduous, herbaceous perennial that reaches approximately 81cm in height. It forms clumps of arching strap-shaped leaves and orchid-like, medium blue flowers with a green star-shaped throat to 18cm across in summer. Flowers last no more than 24 hours, opening late in the day and remaining open during the night

Position

Full sun, Partial shade

Soil Types

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

Position

Full sun Partial shade
Aspect
South–facing or West–facing
Exposure
Exposed or 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)
H6

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Asphodelaceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Clump forming
Potentially harmful
TOXIC to pets (cats) - see the HTA guide to potentially harmful plants for further information and useful contact numbers
Genus
Hemerocallis may be evergreen or herbaceous perennials, with narrow, strap-shaped leaves and funnel-shaped flowers on erect stems in late spring or early summer
Name Status
Accepted

How to Grow

Cultivation

Grow in fertile, moist but well-drained soil preferably in full sun. Flowering is likely to be poor in shadier situations. Tolerant of heavy clay and poorer soils. May need watering in spring to early summer in dry conditions to ensure flowering. See Hemerocallis cultivation or daylily cultivation for details

Propagation

Propagate by division in early spring or early autumn

Suggested planting locations and garden types

  • Cottage and informal garden
  • Coastal
  • Flower borders and beds

Pruning

Cut back flower stems after flowering has finished. Remove dead foliage as required

Pests

May be susceptible to aphids, slugs, snails, hemerocallis gall midge, glasshouse red spider mite and thrips

Diseases

May be susceptible to fungal leaf spot and rust diseases or bacterial leaf and stem rot