We have found 21 plants that meet your criteria.

Price Pruned
Mexican Giant Hyssop ‘Agastache Blue Fortune’ Spires of lilac flowers and aromatic leaves NOW £5.49 Buy
Price Pruned
Lavender ‘Lavandula angustifolia Munstead’ A compact variety with blue-purple flowers NOW £4.99 Buy
Catnip ‘Nepeta racemosa Walker's Low’ Long flowering period £5.99 Buy
Catmint ‘Nepeta subsessilis Cool Cat’ Lavender-blue flowers. Great for a herb garden £5.99 Buy
Catmint ‘Nepeta subsessilis Washfield’ Pretty catmint with bright blue flowers £5.99 Buy
Catmint ‘Nepeta x faassenii’ Loose drifts of lavender flowers. Great for edging £5.99 Buy
Catmint ‘Nepeta x faassenii Kit Cat’ A dwarf variety with purple flowers £5.99 Buy
Russian Sage ‘Perovskia Blue Spire’ Violet-blue flowers and silvery foliage. Great planted en masse £7.99 Buy
Price Pruned
Perennial Phlox ‘Phlox paniculata Blue Paradise’ Fragrant violet flowers all summer NOW £5.49 Buy
New
Spanish Sage ‘Salvia lavandulifolia’ A great alternative to common sage £4.99 Buy
Bog Sage ‘Salvia uliginosa’ Intense blue flowers £5.99 Buy
Salvia May Night ‘Salvia x sylvestris Mainacht’ Large indigo-blue flowers £5.99 Buy
Common Lilac ‘Syringa vulgaris Katherine Havemeyer’ Wonderful scented lavender-purple flowers £9.99 Buy
Price Pruned
Butterfly Bush ‘Buddleja Lochinch’ Fragrant violet-blue flowers all summer NOW £5.99 Buy
Giant Catmint ‘Nepeta grandiflora Wild Cat’ A giant catmint with deep purple-blue flowers £5.99 Buy
Price Pruned
Catmint ‘Nepeta Six Hills Giant’ A hardy catmint with lavender flowers NOW £4.99 Buy
Russian Sage ‘Perovskia abrotanoides’ Silvery white aromatic foliage with long lasting blue flowers £7.99 Buy
Price Pruned
Russian Sage ‘Perovskia atriplicifolia Little Spire’ A shorter form of the popular Russian sage NOW £7.99 Buy
Rosemary ‘Rosmarinus officinalis Miss Jessopp's Upright’ Lavender-blue flowers £5.99 Buy
Purple Sage ‘Salvia officinalis Purpurascens’ Attractive red-purple young leaves £4.99 Buy