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AGM plants have been through a rigorous trial and assessment programme. They are:
This plant will provide nectar and pollen for bees and the many other types of pollinating insects.
It is included in an evolving list of plants carefully researched and chosen by RHS experts. Divided into 3 groups these lists, linked below, are maintained by a team of RHS staff and are reviewed annually.
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Other common names perennial cornflower great blue-bottle
mountain bluet mountain centaury
Synonyms Cyanus montanus
Family Asteraceae
Genus Centaurea may be annuals, perennials or subshrubs, with simple or pinnately lobed leaves and showy thistle-like flowers-heads, often with enlarged outer florets
Details C. montana is a rhizomatous perennial with simple or lobed leaves, hairy beneath, and blue flower-heads 5cm across, reddish in the centre, from late spring to summer
Plant range Mts of Europe
Foliage Deciduous
Habit Spreading / Branched
Hardiness
All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets
H7
Full Sun
Partial Shade
Aspect South-facing or North-facing or West-facing or East-facing
Exposure Exposed or Sheltered
Chalk
Clay
Loam
Sand
MoistureMoist but well-drained
SoilChalk, Clay, Loam, Sand
pHAcid, Alkaline, Neutral
Ultimate height 0.1-0.5 metres
Ultimate spread 0.5-1 metres
Time to ultimate height 2-5 years
Cultivation Best grown in moist but well-drained soil in sun or partial shade, needs staking
Propagation Propagate by seed sown in pots in a cold frame in spring or propagate by division in spring or autumn
Suggested planting locations and garden types Cut Flowers Flower borders and beds Coastal Prairie Planting Cottage & Informal Garden Wildlife Gardens
Pruning Deadhead regularly to prolong flowering
Pests Generally pest free
Diseases May be affected by powdery mildews
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