The best blue flowers: shades of sky, sea, rich royal and navy will intensify your garden on grey days - and bees love them

Blue, cool and serene, is the most elusive colour in the garden and yet it is one that everybody loves. Even bees are more drawn to it than any other flower colour.

True blues — sky blue, royal blueand even navy — are trickier to source than the lavender blues and purples of more commonplace campanula, salvia and catmint. It is possible,though, to find them, and the beautyof blue — aside from the associationsof sea and sky — is that it intensifies in colour on a grey day, putting other plants in the shade.

High summer is a great time to showcase blues in the border. Delphiniums provide sensational shades but are difficult to grow, especially with this year’s heavy onslaught of slugs and snails. However Anchusa azurea Loddon Royalist makes a great vertical substitute and its three-foot flower stems offer the most stunning shade of rich royal blue. An ideal partner would be acid-green euphorbia or Alchemilla mollis.

SEA HOLLY'S SINGIN' THE BLUES

If you can provide it with a welldrained, sunny site, Eryngium zabellii Big Blue, a large-flowered variety of sea holly, will reward you with fabulous thistle-like heads and stems, all in an extraordinary metallic powder blue.

Alliums, with their pompom heads of mauves and purples, are indispensable in the summer garden, but you can make them work harder, and vary the colour palette, by introducing the lesser known Allium caeruleum, which, as the name suggests, is a light cerulean. Scatter the bulbs through the border this September and watch it multiply year after year to create highlights of fuzzy blue that look wonderful with every shade of foliage and flower.

Blue clematis? Why not? Bypass the seductive purples of the viticella group of clematis for a beguiling shade of light blue. Free-flowering Prince Charles is at its finest weaving through pink or yellow climbing roses and keeps on blooming until early autumn; just cut the long stems back hard in late winter for another regal performance the following year.

Tweedia caerulea is a smaller, twining climber, beloved by butterflies, that has exquisite starry flowers of a unique pale milky turquoise. This South American exotic is, unsurprisingly, not hardy, but I have seen it on a south-facing Hampstead patio, twirling merrily around a kitchen window, where it has been happily sited for some years. With a little thought, you can get summer containers to really sing the blues. Don’t overlook ubiquitous lobelia, available at every garden centre. To create a cloud of sky blue, or a deeper sapphire, in a group of potted plants, it is unbeatable. Just try putting baby plants around crimson bedding dahlias, apricot begonias and even tumbling tomatoes, scarlet or golden, for a flattering blue ruffle.

Convolvulus mauritanicus is the dainty, better-behaved bindweed you do want in your garden, or, more specifically, in your containers and hanging baskets, where it will merrily produce its trails of blue-green foliage studded with soft blue trumpet flowers, right through until September. In sheltered town gardens, planted as edging for raised beds or window boxes, this Mediterranean bindweed will make it through winter.

Anagallis monellii Sky Lover, aka the shrubby pimpernel, is more than a team player, and, with its profusion of pink-centred flowers that are a piercing gentian blue, deserves a container all to itself.

Agapanthus, coming into bloom just now, are the plants to add height and structure. Some varieties can be a wishy-washy lavender-blue, but Midnight Star and Navy Blue, both 36in, offer the deepest and most dramatic shades of all. Team them with white agapanthus for a crisp combo of navy blue and white, and then, as back-up, add at a lower level, in separate pots, the fresh white daisy flower osteospermum, that is magically centred with a dollop of navy.

You could also sow a few easy blue-flowered annuals at the end of this summer for earlier, stronger flowers next year. Take your pick from cornflower Centaurea cyanus Blue Boy, that is almost cobalt in colour; sky blue Nigella damascena Miss Jekyll, and borage, with those starry azure flowers that look so good dropped into a glass of Pimm’s or Prosecco. Call it your blue heaven.