The degree of a flower's blue color may lie in the eyes of the beholder. The blooms on many plants commonly described as blue are often closer to lavender or purple. Gardeners nonetheless have a wide range of authentically blue flowering plants from which to choose. The unassuming buds on these plants open to reveal striking blossoms ranging from sky to navy blue.
Cranesbill "Johnson's Blue"
Cranesbill (Geranium) "Johnson's Blue" is a summer blooming perennial that grows in USDA plant hardiness zones 3 and higher. Rare among geraniums, its blue blooms appear between June and September above a mound of foliage standing 18 inches high and up to 30 inches wide. Opening from tiny clusters of spherical buds, its five-petaled, sky blue blossoms show up well against the plant’s deep green leaves. An attractive edging or ground cover plant, "Johnson's Blue" likes organically rich, moist soil and full sun to partial shade, according to the Missouri Botanical Garden.
Siberian Iris "Ego"
Handling winter temperatures in USDA zones 4 and above, Siberian iris (Iris) "Ego" has narrow, tightly furled buds that open to elegant, blue iris blossoms in May. Its erect stems stand up to 30 inches high above narrow, arching green leaves that hold their color into autumn. Making an impressive display planted in groups, "Ego" thrives in boggy areas, advises the Missouri Botanical Garden. In the right conditions, it will form clumps that crowd out weeds. This iris likes locations in full sun to partial shade and performs best in moist, rich soil.
Kalimeris "Blue Star"
An aster family perennial cold-tolerant in USDA zones 5 and higher, Kalameris (Kalimeris incise) "Blue Star" forms 12- to 18-inch clumps of narrow, lancelike green leaves. Resembling daisies, its June-to-September blooms are yellow-centered with pale blue petals (rays). Cutting back its stems after it flowers may result in a flush of autumn bloom, states the Missouri Botanical Garden. This plant handles heat, humidity and dry or wet weather. It performs best in full sun and averagely moist, well-drained soil.
Hyacinth "Blue Jacket"
A bulb plant, hyacinth (Hyacinthus orientalis) "Blue Jacket" brings its delightful perfume to March and April gardens. Up to 12 inches high, it has arching, starlike medium green leaves. Its densely packed, green buds open into a spire of tubular, navy blue flowers. Hardy to USDA zone 4 and above, the bulbs flower best in the first year after planting, advises the Missouri Botanical Garden. Most dramatic planted in groups of between six and 15, "Blue Jacket" likes full sun and rich, well-drained soil.