Centaurea montana 'Purple Heart' (Perennial cornflower 'Purple Heart'): Large white cornflower-like flowers with violet central markings. To 30cm. Hardy

Digitalis purpurea 'Alba' (White foxglove): Pure white flowers on tall spires in late spring. Biennial so keep and re-sow the seed

Penstemon 'White Bedder': Pure white tubular flowers over semi-evergreen foliage. Frost-hardy perennial. Up to 60cm.

Saxifraga x urbium (London Pride): Wiry stems topped with dainty pale pink flowers over ground evergreen rosettes of green leaves with creamy yellow markings.