Violet, the shortest visible wavelength of light is the least visible color, ideal for shadows, but challenging for the gardener.
From “A Gardener Comes to Terms with Violet”:
You might believe the marriage of sexy red with faithful blue would create a perfectly harmonious color. But violet seems to me a more violent clash of bloody red and bruised blue, passive and aggressive. Vibrating in these two fields gives violet a visual nap, sumptuous as velvet, turbulent as unsettled seas. Of all the colors, it is the one that befuddles me the most.

Winter/Spring

Allium ‘Globe Master’, A. ‘Mars’, A. ‘Purple Sensation’,
Aquilegia atrata
Baptisia australis
Camassia quamash
Crocus tommasinianus ‘Barr’s Purple’, C. ‘Lilac Beauty’, C. ‘Ruby Giant’
Crocus vernus ‘Flower Record’, C. ‘Grand Maitre’, C. ‘King of the Striped’, C. ‘Lady Killer’
Daphne genkwa
Erysimum ‘Bowles Mauve’

Geranium ‘Nimbus’
Hyacinthus orientalis ‘Miss Saigon’, H. ‘Peter Stuyvesant’, H. ‘Woodstock’

Iris douglasiana, I. missouriensis, I. pallida ‘Variegata’, I. ×robusta ‘Gerald Darby’, I. versicolor
Paulownia tomentosa
Rhododendron impeditum

Syringa vulgaris ‘President Lincoln’, S. ‘Sensation’, S. ‘My Favorite’
Tulipa ‘Blue Amiable’, T. ‘Blue Parrot’, T. ‘Negrita’, T. ‘Purple Prince’, T. ‘Queen of the Night’, T. ‘Rembrandt’s Favorite’, T. ‘Synaeda Blue’

Summer/ Fall
Aconitum ‘Bressingham Spire’

Aster ×frikartii ‘Monch’
Aster nova-angliae ‘Hella Lacy’, A. ‘Treasure’

Callicarpa bodinieri ‘Profusion’
Campanula latifolia, C. ‘Sarastro’

Clematis ‘Rooguchi’, C ×jackmanii, C. alpina
Cynara cardunculus
Geranium ‘Rozanne’

Hemerocallis ‘Little Grapette’, H. ‘Big Blue’
Liatris spicata
Perovskia atriplicifolia

Salvia guaranitica ‘Amistad’, S. leucantha‘ Santa Barbara’, S. nemerosa ‘Amethyst’, S.n. ‘Cardonna’, S. verticillata ‘Purple Rain’
Tricyrtus ‘Tojen’, T. formosana
Verbena bonariensis, V. ‘Homestead Purple’
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