Blue-flowered plants can bring a sense of coolness, peace and tranquility to your garden. Whether you desire a bright blue, pastel sky blue or deep midnight blue shade, there is a flower to meet your needs. Many blooms which are described as being blue tend toward a purplish-blue violet, while others are more in the reddish-blue or magenta range, so it is helpful to view a blue-flowered plant in person before adding it to your garden.
Blue-flowered spring bulbs abound. Chionodoxa or glory of the snow, so named because its very early bloom time may leave it peeking from the snow, come in blue or blue and white. Tiny scilla, or Siberian squill, are available in an intense royal blue shade which provides a good foil for pink tulips and yellow daffodils, recommends the Brooklyn Botanic Garden. Fragrant hyacinth, blooming a little later in spring, can be found in a sky blue shade as well as a deeper purple-blue.
Ageratum is a reliable source of blue in summer beds or containers. Its fuzzy flower panicles come in a soft blue and are useful for providing contrast to the more commonly found pink, yellow or white annuals. The forget-me-not, or Myosotis, is a dainty, old-fashioned garden favorite, with a white or yellow eye set in a sky-blue flower. Calibrachoa, also called million bells, comes in both light and dark blue shades and is often used in summertime hanging baskets. The deep, electric blue Lobelia is another container and hanging basket favorite.
Irises, including the Siberian and Japanese types as well as the bearded varieties, provide many shades of blue, from pale to deep, early in the summer. Veronica (sometimes called speedwell) plants can be ground-hugging, like the periwinkle-colored “Waterperry Blue,” or upright and clump-forming; “Crater Lake Blue” and “Sunny Border Blue” are just two of the reliable summer-blooming, blue-flowered veronicas. Campanula carpatica, or Carpathian bellflower, is also known for its bright blue, bell-shaped flowers in varieties such as “Blue Clips.” If you wish to have a blue flower for the back of the border, look no further than the stately Delphinium. Its tall spikes of bloom can be found in many different shades and intensities of blue. One of the few shade perennials offering blue flowers is Aconiutum, or monkshood. Its tall spires provide bloom from late summer to late autumn in medium blue, blue and white, and deep navy-colored flowers.
Don't forget vines if you want to add blue flowers to your garden. Probably the best-loved of all blue-flowered vines is the morning glory variety called “Heavenly Blue.” Given a sunny spot, it will provide dozens of new blooms every day, from mid-summer on, says the University of Florida Extension. The clematis is a perennial vine available in a number of blue-flowered cultivars, such as “Belle of Woking,” with a double light-blue rosette-shaped blossom; and “Will Goodwin,” “Perl D’Azur” and “Mrs. Cholmondeley,” all with pastel blue flowers.