We have found 21 plants that meet your criteria.

granny's bonnet
Aquilegia vulgaris var.stellata 'Black Barlow' (Barlow Series) granny's bonnet Striking dark purple, double flowers £7.49 Buy
granny's bonnet
Aquilegia vulgaris 'William Guinness' granny's bonnet Unusual purple-black flowers £7.49 Buy
clematis (group 3)
Clematis 'Black Prince' clematis (group 3) Beautiful deep purple flowers £12.99 Buy
clematis (group 3)
Clematis 'Warszawska Nike' clematis (group 3) Sumptuous deep purple flowers, £9.99 Buy
dusky cranesbill
Geranium phaeum dusky cranesbill Small, deep maroon flowers. Good for groundcover £7.49 Buy
dusky cranesbill
Geranium phaeum var. phaeum 'Samobor' dusky cranesbill Small, purple-black flowers. Good for damp... £7.49 Buy
Price Pruned
Lenten Rose hellebore
Helleborus × hybridus 'Harvington Double Lime' Lenten Rose hellebore A gorgeous, new variety NOW £11.99 Buy
Price Pruned
Lenten Rose hellebore
Helleborus × hybridus Harvington double purple Lenten Rose hellebore Stunning double flowers NOW £11.99 Buy
Price Pruned
Lenten Rose hellebore
Helleborus × hybridus Harvington Smokey Blues Lenten Rose hellebore Unusual, dark purple flowers... NOW £12.99 Buy
lily
Lilium 'Dimension' lily Brooding and sumptuous colour £5.99 Buy
New
lily bulbs
Lilium 'Sixth Sense' lily bulbs Brooding colour for the summer border £2.99 Buy
black-eyed Susan
Rudbeckia occidentalis 'Green Wizard' black-eyed Susan Bright green sepals with black centres £6.99 Buy
coneflower
Rudbeckia occidentalis 'Green Wizard' coneflower Extraordinary and exotic-looking flowers £2.99 Buy
black elder (syn. Black Beauty)
Sambucus nigra f. porphyrophylla 'Gerda' (PBR) black elder (syn. Black Beauty)... Dramatic purple foliage £10.99 Buy
red hook sedge
Uncinia rubra red hook sedge Wonderful deep bronzy-red foliage £7.99 Buy
Price Pruned
Lenten Rose hellebore
Helleborus × hybridus 'Harvington Shades of the Night' Lenten Rose hellebore Early spring flowers in... NOW £9.99 Buy
beard tongue
Penstemon 'Raven' beard tongue Dramatic, deep purple, foxglove-like flowers £6.99 Buy
Price Pruned
tree peony / tree paeony
Paeonia delavayi tree peony / tree paeony... Tree peony with deep, maroon flowers NOW £19.99 coming soon
New
hyacinth
Hyacinthus 'Dark Dimension' hyacinth Darkly delicious £3.99 coming soon
Polyanthus Gold Lace
Primula Gold-laced Group Polyanthus Gold Lace This new variety has all the old world charm £5.99 coming soon