Veronicastrum sibiricum 'Kobaltkaars'

RHS Plant Profile
Culver's root 'Kobaltkaars'

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Herbaceous Perennial
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An upright, clump-forming, rhizomatous perennial to 1.4m, with large, broadly linear green leaves arranged in whorls around the stems. Tall, thick spikes of lilac-blue flowers appear from June to August

Position

Full sun, Partial shade

Soil Types

Chalk, Clay, Loam, Sand

Max Height

1-1.5 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
2–5 years
Max Spread
0.1-0.5 metres
Max Height
1-1.5 metres

Growing Conditions

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

Position

Full sun Partial shade
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)
H7

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Plantaginaceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Clump forming
Genus
Veronicastrum are tall herbaceous perennials with erect stems bearing narrow leaves in whorls, and long terminal racemes of small flowers in summer
Name Status
Unresolved

How to Grow

Cultivation

Grow in moderately fertile, humus-rich, moist soil in sun or partial shade

Propagation

Propagate by by sowing seed in pots in a cold frame in autumn, or by division in spring

Suggested planting locations and garden types

  • Cottage and informal garden
  • Flower borders and beds

Pruning

Cut back old stems in early spring

Pests

May be susceptible to aphids

Diseases

May be susceptible to leaf spot, downy mildews and powdery mildews