We have found 16 plants that meet your criteria.

Price Pruned
Granny's Bonnet ‘Aquilegia vulgaris var. stellata Black Barlow’ Striking dark purple, double flowers NOW £4.99 Buy
Dusky Cranesbill ‘Geranium phaeum’ Small, deep maroon flowers. Good for groundcover £5.99 Buy
Price Pruned
Dusky Cranesbill ‘Geranium phaeum var. phaeum Samobor’ Small, purple-black flowers. Good for damp or dry shade NOW £5.49 Buy
Trillium ‘Trillium cuneatum’ Big maroon petals £3.00 Buy
Trillium ‘Trillium recurvatum’ Great for naturalising in woodland £3.00 Buy
Double Late Tulip ‘Tulipa Black Hero’ Almost black double flowers £5.00 Buy
Tulip Black Jewel ‘Tulipa Black Jewel’ A tall, very dark coloured tulip £7.50 Buy
Fringed Tulip ‘Tulipa Curley Sue’ Delicately fringed flower petals £4.00 Buy
Triumph Tulip ‘Tulipa Negrita’ A sturdy tulip with rich colour £3.00 Buy
Single Late Tulip ‘Tulipa Paul Scherer’ Possibly the darkest purple tulip £4.00 Buy
Single Late Tulip ‘Tulipa Queen of Night’ Velvety, dark maroon blooms £3.00 Buy
Granny's Bonnet ‘Aquilegia vulgaris William Guinness’ Unusual purple-black flowers £5.49 Buy
Lenten Rose ‘Helleborus x hybridus Harvington Shades of Night’ Early spring flowers in shades of deep purple £9.99 Buy
Harvington Hellebore ‘Helleborus x hybridus Smokey Blue’ Unusual, dark purple flowers with a deep blue sheen £9.99 Buy
Parrot Tulip ‘Tulipa Black Parrot’ Dramatic, blackish-purple, cup-shaped flowers £5.00 Buy
Triumph Tulip ‘Tulipa Havran’ Darkest blackcurrant coloured blooms £3.00 Buy