Answer: Only a few perennials appreciate wet feet, so your choices are limited. Mophead hydrangea, Camellia and hardy fuchsia are shrubs to try. Perennials include Aconitum (Wolfsbane/ monkshood) Various species and cultivars with flowers in purple, blue and cream in mid to late summer.
Anemone nemorosa (Wood anemone, windflower) Low growing and spreading where happy. Delicate white flowers in spring over deeply lobed leaves or more expensively in shades of light to mid blue.
Aquilegia - various species (Columbine) Perennial forming clumps of pretty green or greyish leaves with taller stems of bell shaped flowers, mostly with distinctive spurs. Vary in size from 6" alpines to 2', and in color from yellow, red white and blue including combinations. Tend to be short lived but seed readily and cross breed prolifically.
Asarum europaeum Evergreen, creeping perennial with kidney shaped glossy leaves with inconspicuous flowers.
Dodacatheon (Shooting stars) Rosette of leaves with pink, mauve or white cyclamen like flowers on tallish stalks. Dentatum and pulchellum prefer dense shade others partial shade.
Epimedium - more or less evergreen some with tinted leaves, fairly small flowers in shades of pink white and yellow. Will spread into large clumps when happy.
Galium odoratum (sweet woodruff) Sweet smelling when dried, creeping ground cover with bright green leaves and tiny white flowers.
Geranium - Many hardy species and cultivars are suitable for shade, some are specifically mentioned below but others are worth trying. Many come easily from seed and many flower for long periods:
Geranium macrorhizum Various cultivars with slightly different colored flowers on a theme of pink. Excellent spreading ground cover, easy and reliable flowerer.
Geranium nodosum -Shiny green leaves with sparse flowers in purple or lilac. Easy even in dry shade.
Heuchera sanguinea (coral bells) Evergreen clumps of leaves with various silver veinings, purple shadings or grey to pewter bloomed surface. Spikes of small flowers in shades of cream, green or pink in spring. Some cope better than others with dryness.
Hosta - Deciduous clumps of succulent leaves in shades of grey green and gold with various variegations. Some colors need specific shade conditions to bring out their best. Racemes of bell shaped flowers in pastel shades of mauve white or cream flowers.
Impatiens - Fleshy, tender perennial. Easily propagated from cuttings and kept indoors over winter, or use as annual. Bright flat upward facing flowers in shades of red, pink and white. Varying types and sizes available from low growing to 18" tall. Moisture essential.
Liriope muscari Spikes of lavender flowers in autumn from clumps of grassy leaves. Prefer acidic soils.
Lunaria (Honesty) Honesty comes with green or white variegated leaves with white or pink/purple flowers which produce those translucent oval remains of seed pods so beloved of dried flower arrangers. Lunaria rediviva is a perennial with highly scented much less conspicuous flowers.
Pachysandra terminalis Small white flowers, evergreen spreading to 8" tall. Variegated form available. Good ground cover.
Polygonatum (Solomon's Seal) Arching stems with dangling white bells. Spring shoots like shepherds crooks.
Primulas various species and cultivars From native primroses to candelabra primulas, all shades and heights.
Pulmonaria (Lungwort) Low heaps of deciduous leaves plain green, or spotted or marked with silver. Spring flowers in shades of red, pink, purple blue or white. Will just about survive summer dryness dying back and resprouting in autumn but better with constant moisture.
And, of course, ferns of all kinds!
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