Penstemon strictus

RHS Plant Profile
Rocky Mountain penstemon

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Other common names

stiff beard-tongue

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Herbaceous Perennial
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Evergreen perennial to 75cm tall, forming large clumps of rich green, lance-shaped, slender leaves and producing upright spikes of royal blue to purple tubular flowers, over a long period from early summer

Position

Full sun

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
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)
H5

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Plantaginaceae
Native to GB/Ireland
No
Foliage
Semi evergreen
Habit
Clump forming
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
Correct
Plant Range
United States

How to Grow

Cultivation

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

Propagation

Propagate by seed in late winter or spring, softwood cuttings in early summer or semi-ripe cuttings in midsummer

Suggested planting locations and garden types

  • City and courtyard gardens
  • Coastal
  • Cottage and informal garden
  • Gravel garden
  • Patio and container plants
  • Prairie planting
  • Wildlife gardens
  • Cut flowers
  • 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

May be susceptible to downy mildews, grey moulds, powdery mildews and a fungal leaf spot