Agastache rugosa 'Liquorice Blue' (Korean mint 'Liquorice Blue'): Spikes of warm blue lipped flowers from late June onwards. Very attractive to bees. Aromatic foliage. To 1.5m. Hardy in light soils. [Collect Only]

Amsonia tabernaemontana (Blue dogbane): Starry blue flowers on strong stems with willowy green leaves. Hardy. Up to 90cm. [Collect Only]

Aster macrophyllus 'Twilight' (Syn. Eurybia x herveyi): Lavender-blue flowers with a yellow centre in late summer. Mildew-resistant foliage. An earlier flowering variety. Height to 1m.

Baptisia 'Indigo Spires' (Indigo weed 'Indigo Spires'): Spikes of violet-blue pea-like flowers with a yellow edge above a mound of grey-green foliage. Long flowering. Hardy. Up to 1.2m

Baptisia australis (Indigo weed): Spires of lipped indigo flowers over olive-green foliage. Flowering height 1.2m.

Campanula portenschlagiana 'Resholdt's Variety' (Wall bellflower 'Resholdt's Variety'): Carpeting alpine with brilliant blue flowers over a long flowering period in summer.

Catananche caerulea (Cupid's dart): Masses of papery lavender blue flowers held on wiry stems all summer. Seed heads turn silver in late summer. Good dried flower. Up to 60cm.

Catananche caerulea 'Major' (Cupid's dart 'Major'): Masses of papery blue flowers held on wiry stems all summer. Seed heads turn silver in late summer.

Centaurea montana (Perennial cornflower): Large blue flowers in early summer, repeated later in year if cut back. Very attractive to bees. To 50cm. Hardy

Eryngium bourgatii 'Picos Amethyst'': Stunning steely blue flowers on stiff stems with a gorgeous purple tint.

Eryngium bourgatii Graham Stuart Thomas's selection (Sea Holly Graham Stuart Thomas's selection): Spiny, violet blue flowers in summer of even spinier blue-green leaves with white mid-ribs.

Eryngium planum 'Blue Hobbit' (Sea Holly 'Blue Hobbit'): A more compact form with steely blue flowers on dark stems. Spiny glaucous foliage. Loves sunshine and very well-drained gritty soil. Hardy. Up to 30cm.

Eryngium x zabelii 'Big Blue (Sea Holly 'Big Blue): Large electric-blue thimble-shaped flowers with a spiky collar and silver-green foliage. Long flowering and bee-friendly. Hardy. Up to 75cm

Eryngium x zabelii 'Jos Eijking' (Sea Holly 'Jos Eijking'): Large steely blue bracts surround a dome of tiny blue flowers in summer. Long-lasting flowers.Thrives in a sunny,dry spot. To 70cm. Hardy. [Collect Only]

Nepeta 'Six Hills Giant' (Catmint 'Six Hills Giant'): A vigorous sun lover which will soon make a generous clump. Spikes of tiny purple flowers over aromatic grey/green foliage.

Nepeta grandiflora 'Summer Magic' (PBR) (Catmint 'Summer Magic'): A more compact, upright growing variety of Catmint with aromatic grey foliage and spikes of lavender blue flowers. Hardy. Up to 35cm.

Nepeta racemosa 'Walker's Low' (Catmint 'Walker's Low'): Forms neat mounds of silvery green foliage, topped with masses of lavender blue flowers in early summer. Up to 60cm. Hardy.

Nepeta sibirica 'Souvenir d'Andre Chaudron' (Catmint 'Souvenir d'Andre Chaudron'): One of the largest flowers and more upright growth than other catmints. Aromatic lance shaped leaves. Hardy. Up to 45cm.

Nepeta x faassenii 'Kit Cat' (Catmint 'Kit Cat'): A compact variety of catmint making a neat mound of aromatic green foliage and clusters of lavender blue flowers. Hardy. Up to 30cm.