Agastache 'Summer Sky'

RHS Plant Profile
giant hyssop 'Summer Sky'

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giant hyssop 'Summer Sky' RHS
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Herbaceous Perennial

A compact, bushy perennial to 60cm tall with ovate, aromatic leaves. Flower spikes comprising whorls of small, tubular, violet-blue flowers with darker calyces are borne from summer into autumn

Position

Full sun

Soil Types

Chalk, Loam, Sand

Max Height

0.5-1 metres

Max Spread

0.1-0.5 metres

Size

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

Growing Conditions

Chalk Loam Sand
Moisture
Moist but well–drained or 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)
H3

Colour & Scent

Fragrance Foliage
Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Lamiaceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Bushy
Genus
Agastache are herbaceous perennials with simple, aromatic leaves and small 2-lipped tubular flowers in whorls forming dense spikes, in summer and autumn; some are rather tender but can be grown as annual bedding
Name Status
Accepted

How to Grow

Cultivation

Grows best in well-drained, fertile soils in full sun

Propagation

Propagate by division or by semi-ripe cuttings

Suggested planting locations and garden types

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

Pruning

Remove spent flowering spikes through the season to prolong flowering

Pests

Generally pest-free

Diseases

May be susceptible to powdery mildews