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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.
Dove Cottage Hybrid is an upright perennial to 60cm tall with sky blue to navy blue, cone-shaped flowerheads surrounded by spiny, blue-silver bracts borne on branching stems in summer
'Picos Blue' is a larger and more intensely blue cultivar than is typical of the species. Leaves are grey-green with white veining and flowers an intense blue with a starry, thistle-like form. Usually reaches 60cm in height
E. maritimum is a clump-forming perennial to around 60cm in height. Leaves are waxy, stiff and spiny, blue-green in colour with white veins. Flowerheads of globular blue umbels are borne in April to September surrounded by collars of spiky bracts
'Oxford Blue' is an erect herbaceous perennial to 40cm, with clumps of deeply divided basal leaves with prominent whitish veins. Cone-like, deep blue flower-heads 2cm in length are surrounded by silvery-blue, spiny bracts
'Silver Ghost' is an erect, branching biennial with cone-like heads of blue flowers surrounded by spiny, silvery-white bracts
'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
E. amethystinum is a semi-evergreen, clump-forming perennial to around 70cm tall forming a rosette of divided basal leaves. Egg-shaped to rounded, steel blue flowerheads to 2cm long are borne on upright, branching stems often also coloured a deep blue; each flowerhead is surrounded by spreading blue-silver bracts
'Blue Jackpot' is a herbaceous perennial with stiff, branched stems above a basal clump of divided leaves. In mid- to late summer produces cones of tiny blue flowers surrounded by a ruff of large, finely divided, blue bracts
'Blaukappe' is a clump-forming perenniual with rounded basal leaves; erect, branched stems bear deeply-lobed, blue-tinged, spiny leaves and small, steel-blue, terminal flower-heads with narrow, spiny bracts in summer and early autumn
'Physic Purple' is an evergreen, herbaceous perennial with blue-green, sword-shaped leaves up to 2m long. Small, cone-like clusters of tiny red-purple flowers are produced on massive, branched flower stems up to to 4mtall, in from late summer to mid autumn
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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.