Ageratum houstonianum 'Blue Horizon'

RHS Plant Profile
Mexican paintbrush 'Blue Horizon'

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Mexican paintbrush 'Blue Horizon' RHS 1999
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Annual Biennial
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A mound-forming annual with long-stemmed violet-blue flower-heads. Good for cutting

Position

Full sun

Soil Types

Chalk, Clay, Loam, Sand

Max Height

0.1-0.5 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
1 year
Max Spread
0.1-0.5 metres
Max Height
0.1-0.5 metres

Growing Conditions

Chalk Clay Loam Sand
Moisture
Moist but 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)
H2

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Asteraceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Bushy
Genus
Ageratum can be annuals, perennials or shrubs, usually bushy in habit, with simple ovate leaves and small fluffy blue, pink or white flower-heads in summer and autumn
Name Status
Accepted

How to Grow

Cultivation

This genus is ideal edging for bedding schemes; bearing weather-resistant flowers on young plants. To prolong flowering, keep soil or growing media moist.

Propagation

Propagate by seed

Suggested planting locations and garden types

  • City and courtyard gardens
  • Patio and container plants
  • Cottage and informal garden
  • Flower borders and beds
  • Garden edging

Pruning

No pruning required

Pests

Generally pest-free

Diseases

Generally disease-free