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All ratings refer to the UK growing conditions unless otherwise stated. Minimum
temperature ranges (in degrees C) are shown in brackets
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.
E. ritro is a robust, upright herbaceous perennial, with jaggedy-divided, prickly dark green leaves whitish beneath. Rounded, violet-blue flower heads on silvery, branched, leafy stems
'Taplow Blue' is a robust, upright herbaceous perennial, with divided, prickly dark green leaves whitish beneath. Rounded, steel-blue flower heads on branched, leafy stems
'Arctic Glow' is a vigorous perennial with sturdy stems to 1m tall, with spiny, deeply divided leaves and globose white flower-heads borne in mid and late summer
'Veitch's Blue' has slightly darker blue spherical flowerheads than E. ritro, is good for cutting and flowers more than once in a season
E. ritro subsp. ruthenicus is an erect herbaceous perennial to 1m tall, with glossy, lobed, thistle-like leaves white beneath, and globose, bright blue flower-heads on long, white stems in late summer
E. spiniflora has a spherical or cylindrical dull green stem up to 15cm thick with up to 20 ribs and clusters of long, strong spines. Trumpet-shaped pale purple, white or pink flowers are produced in summer
E. oxygona is a cactus with clustered, globose to shortly cylindrical, ribbed stems to 20cm tall, bearing short, blackish spines and funnel-shaped white flowers to 20cm across, opening in late afternoon
E. backebergii subsp. backebergii is a cactus with solitary or clustered, deeply ribbed, globose stems to 5cm across, bearing brown to grey spines; flowers up to 9cm across, carmine-red to violet with a paler centre
E. bannaticus is a clump-forming perennial with upright, grey, woolly stems and spiny, hairy, grey-green divided leaves. Spherical blue-grey to blue flowerheads, up to 5cm across, are produced in mid- and late summer
E. backebergii subsp. wrightiana is cactus with solitary or clustered spherical stems to 5cm diameter, bearing brown to grey radial spines to 5cm long, and slender-tubed pale or deep red flowers to 7cm across
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We're a UK charity established to share the best in gardening. We want to enrich everyone's life through plants, and make the UK a greener and more beautiful place.