Blue flowers are useful for accenting other colours in the garden, and I always try to have some in bloom from summer through fall. You don’t need many, just a few will do the trick if placed strategically. I find the easiest way to do this is with long-blooming blue salvias.
I have one returning clump of perennial salvia ‘Caradonna’ (Salvia nemerosa ‘Caradonna’, Zone 4), with straight, 18-inch (45-cm) spikes of violet-blue flowers on almost black stems. Each little flower has a wispy pink calyx, giving the stems an almost glowing appearance. It pairs well with the new vividly coloured Echinacea cultivars, and I have it next to a PowWow Wild Berry coneflower (Echinacea purpurea PowWow Wild Berry, Zone 4) I planted this spring.
‘Caradonna’ blooms from June through October if deadheaded and fertilized. The key to getting it to rebloom is to snip off the flower spikes when they’re almost — but not quite — finished. If there are a few small florets still blooming, that’s the time to snip the spike just below the flowers, leaving the foliage on the plant. Then fertilize, and watch for new growth.
Long-blooming Mystic Spires Blue salvia (Salvia ‘Balsalmisp’) is a good, strong blue. It’s perennial in warm climates, but used as an annual in the north, and makes a vigorous clump about 12 inches (30 cm) wide, with 18-inch (45-cm) flower spikes. The flower petals have a soft quality, and many additional spikes surround a dominant central flower stalk. Mine is next to pink perennial geraniums, the low-growing ‘Max Frei’ (Geranium sanguineum ‘Max Frei’, Zone 4); it would also be a lovely companion for roses.
Part of the haul from this spring’s plant buying trip was annual salvia ‘Evolution’ (Salvia farinacea ‘Evolution’), a compact mealy cup salvia with spikes of rich blue flowers that looks like a scaled-down version of salvia ‘Victoria’ (S. f. ‘Victoria’). It’s 12 inches (30 cm) wide and 18 inches (45 cm) tall, and can be used as a bedding plant or in containers. I have mine in a container with dwarf yellow snapdragons, scarlet calibrachoa and chartreuse Helichrysum petiolare ‘Lemon Licorice’. Just a little spot of blue everywhere you look makes the garden brighter.