Penstemon 'Castle Forbes'

RHS Plant Profile
penstemon 'Castle Forbes'

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A compact, bushy, semi-evergreen, drought-tolerant perennial with dark green, strap-shaped foliage. Upright spikes of long-lasting, tubular, rose-red flowers with white throats appear from June to October

Position

Full sun, Partial shade

Soil Types

Chalk, Loam, Sand

Max Height

0.5-1 metres

Max Spread

0.5-1 metres

Size

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

Growing Conditions

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

Position

Full sun Partial shade
Aspect
East–facing or 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)
H4

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Plantaginaceae
Native to GB/Ireland
No
Foliage
Semi evergreen
Habit
Bushy
Genus
Penstemon may be deciduous or evergreen perennials or subshrubs, with simple, narrow leaves and racemes or panicles of bell-shaped or funnel-shaped flowers in summer and early autumn
Name Status
Accepted

How to Grow

Cultivation

Grow in fertile, moist but well-drained soil in full sun or partial shade. In cold areas, protect plant overwinter with a dry winter mulch. See penstemon cultivation for further advice

Propagation

Propagate by softwood cuttings in early summer or semi-hardwood cuttings in midsummer. Propagate by division in spring

Suggested planting locations and garden types

  • City and courtyard gardens
  • Cottage and informal garden
  • Wildlife gardens
  • Flower borders and beds

Pruning

Deadhead after flowering to maintain vigour and prolong flowering, then cut back to 15cm in late winter or early spring

Pests

May be susceptible to slugs, snails, aphids and leaf and bud eelworms

Diseases

Generally disease-free but may be susceptible to powdery mildews and grey moulds