While red, yellow and orange flowers can create a dazzling garden, on warm days days they might heat things up even more. Finding blue flowers to cool down your garden palette, however, requires some effort. Not all flowers called blue live up to their descriptions. They're often closer to purple or lavender than blue. Even so, flowers ranging from pale sky to bright royal to dark blue are available. Use them to build a soothing garden landscape.
Giant Hyssop "Honey Bee Blue"
Giant hyssop (Agastache rugosa) is hardy to winter temperatures of -20 degrees F. Standing up to 3 feet high and 2 feet wide, it has greenish-gray aromatic leaves. Growing wild along roadsides and in open areas across much of the upper Midwest, giant hyssop has also been cultivated as a popular garden plant.
The Honey Bee Blue cultivar, says the Missouri Botanical Garden, produces erect stems bearing spikes of fragrant, bright blue tubular flowers from July to September. Bees and butterflies flock to the blooms. Plant disease-and-pest-resistant Honey Bee Blue in a sunny (for maximum flowering) to partly shady spot with medium, well-drained soil. Established plants handle drought and heat.
Butterfly Bush "Adonis Blue"
Butterfly bush (Buddleja davidii), a deciduous figwort family shrub, is also hardy to -20 degrees. While some butterfly bush plants can reach up to 15 feet high, Adokeep Adonis Blue is a dwarf cultivar between 3 and 5 feet high and wide. Its dense branches produce abundant 8- to-10-inch spikes of dark blue flowers from June to September.
The faintly scented blooms are butterfly magnets, says the Missouri Botanical Garden. They also make good cut flowers. Removing faded flower spikes may extend the blooming season. Narrow, graceful green leaves add to the shrub's appeal. Because of its compact size, Adonis Blue is most impressive planted in groups. It likes full sun and well-drained soil with medium moisture. Cutting it almost to the ground in late winter stimulates growth and flowering.
Clematis (Clematis montana f. grandiflora), a buttercup family vine, handles winter temperatures as low as -25 degrees. Reaching up to 40 feet long and wide, clematis has pure white flowers against bright green foliage in May and June. Clematis Ramona is a smaller--up to 12 feet long and 6 feet wide--cultivar with a longer blooming season.
From May to September, says the Missouri Botanical Garden, Ramona has 7-inch light blue flowers with contrasting red anthers (pollen holders). Both its old and new branches produce blooms. Its dark green leaves make a good background for other flowers when Ramona isn't blooming. The plant's drawbacks include susceptibility to stem rot, wilt, aphid, scale and mites. Use Ramona as a climbing vine on trellises, walls or fences, or let it spread to cover nearby tree stumps or shrubs. It likes full sun with shaded roots and fertile, well-drained soil.