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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 giant marsh marigold
Synonyms Caltha palustris subsp. polypetala
Family Ranunculaceae
Genus Caltha are rhizomatous herbaceous perennials with simple, usually heart-shaped leaves and cup-shaped yellow or white flowers in early spring
Details C. polypetala is a herbaceous perennial, up to 60cm high and 90cm wide, spreading by rooting stems across ground or across water. It has rounded green leaves, the basal leaves up to 10cm across, the stem leaves fewer and smaller, and shining, bright golden yellow flowers, up to 5cm across, from early spring to summer
Plant range Asia
Foliage Deciduous
Habit Clump-forming
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
Aspect South-facing or West-facing or East-facing
Exposure Exposed or Sheltered
Chalk
Clay
Loam
Sand
MoisturePoorly-drained
SoilChalk, Clay, Loam, Sand
pHAcid, Alkaline, Neutral
Ultimate height 0.5-1 metres
Ultimate spread 0.5-1 metres
Time to ultimate height 2-5 years
Cultivation Plant from spring to autumn in full sun, in deep, rich organic soil, at the water's edge or in shallow water up to 15cm deep; mulch annually to conserve moisture
Propagation Propagate by seed, sown fresh in late summer in a cold frame, making sure that the compost does not dry out, or by division in spring
Suggested planting locations and garden types Low Maintenance Cottage & Informal Garden
Pruning No pruning required, though the stems may be cut back after flowering
Pests Generally pest free
Diseases May be affected by powdery mildews and rust diseases
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