Cuphea viscosissima

RHS Plant Profile
blue waxweed

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blue waxweed RHS

Other common names

clammy cuphea, tarweed

Conservatory Greenhouse Bedding Houseplants
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A bushy, half-hardy annual with purple flowers produced over a long period from summer into autumn. The leaves and the stems are both sticky

Position

Full sun, Partial shade

Soil Types

Chalk, Loam, Sand

Max Height

0.1-0.5 metres

Max Spread

0.5-1 metres

Size

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

Growing Conditions

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

Position

Full sun Partial shade
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)
H2

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Lythraceae
Native to GB/Ireland
No
Foliage
Evergreen
Habit
Spreading branched
Genus
Cuphea can be annuals, perennials or evergreen shrubs, often with sticky hairs, opposite, simple leaves and tubular flowers with a showy calyx and small petals
Name Status
Correct

How to Grow

Cultivation

Best grown in well-drained soil in a sheltered site in partial shade or full sun; it benefits from shading from hot sun

Propagation

Propagate by seed; ideally sow direct where plants are to flower

Suggested planting locations and garden types

  • Patio and container plants
  • City and courtyard gardens
  • Flower borders and beds
  • Wall side borders

Pruning

No pruning required

Pests

Generally pest-free

Diseases

Generally disease-free