I recently found an interesting new book, A Book of Blue Flowers by Robert Geneve. Blue is an anthocanin pigment and, in the plant kingdom, is primarily a flower color. It is rarely found elsewhere. It is totally absent, for instance, in fall leaf color where leaf pigments are most readily seen. Fall leaf colors are the result of the emergence of the anthocyanins but only the red pigments manifest themselves. (Yellow is the result of a different group of pigments.)
Blue can also be found as a leaf color in certain grasses such as fescue (Festuca) and Helictotricon and in some conifers. Hostas are another source of blue leaf coloring. In desert plants such as the Agave the blue leaf coloring may be less a case of the presence of anthocyanins and more the result of a waxy leaf covering that makes the green chlorophyll appear to be blue.
Anthocyanin is derived from the Greek for “flower” and “dark blue”. They are responsible for the reds, pinks, purples and blues in flowers. The group of chemical compounds, anthocyanidins, from which the anthocyanins are formed were first isolated from flowers and named for the flowers in which they were discovered. Cyanidin is crimson red and was first found in bachelor buttons (Centaurea cyanus). Pelargonidin is the scarlet from geraniums (Pelargonium). Peonies (Paeonia) provide rosy red peonidin, blue-violet delphinidin comes from delphiniums and purple petunidin was discovered in petunias. When these convert into anthocyanins, through the addition of plant sugars, they provide the endless array of red through purple coloration in flowers.
Geneve goes on to explain that the shade and intensity of flower coloration can be impacted by various elements other than the pigments present. Environmental stress, plant nutrition, cold, and even insect attack can result in the changes in anthocyanin production and variations in flower color. Even flower petal shape can alter the perception of color.
Co-pigmentation or the presence of yellow pigments (flavonols) or colorless pigments (flavonoids) change coloration. The presence of these compounds tends to make a flower bluer. They also change the way an insect sees a flower, as they absorb ultraviolet light which is “seen” by insects.
The pH in the cells of the petals in which anthocyanins are stored play a large role in coloration. The change in pH as the flower ages can change the flower color signaling pollinators that the flower is fertilized or past its prime. In the borage family (Boraginaceae) the flowers change from pink to blue as they age, with both flower colors present on the plant at the same time.
The ability of plant breeders to change the pH in cells and the ability of the anthocyanins to change color at a different pH has given us flower colors not produced by Mother Nature. Blue pansies were the result of plant breeders finding a way to increase the pH in pansy cells to just over 6. A pH that is under 5 results in a red pansy.
Geneve goes on to list just about every blue flower that exists, from the pale blues of striped squill (Puschkinia scilloides) to deep blue of the Welsh poppy (Meconopsis horrdula). Since many “blue” flowers are really purple these shades are included as well. For each of the flowers there is a genus description and a listing of common species and cultivars. He also gives cultural and propagation information.
This is a very specialized book. It might have been improved by a more lengthy discussion of the use of the color blue in the garden, both in color combinations of plants and its effect on the general atmosphere of a planting area. Still it is worth reading if you have an interest in blue or purple flowers.
Blue in the Garden
Blue in the garden is a tranquil color. Massed plantings of blue add coolness and depth to a flower garden or border. Placed at the back of the garden or on the edges, it creates an illusion of distance. Blue plantings will also blend areas together eliminating abrupt beginnings and endings of beds.
A single flower color used in a garden or variations on a single color makes for the most harmonious of garden arrangements. While it is certainly possible to plant an all blue garden, the scarcity of true blue flowers can make it a daunting task. The term “blue”, perhaps because of the rarity of “true blue”, generally covers every shade from purplish aconite to silvery blue-rug juniper. A range of similar shades tends to focus the eye on particulars of the plants and their arrangements. Riotous colors mixed together are distracting to the eye. Care must be taken to choose the appropriate shade of blue and arrange it for the task it is to perform.
Blue flowers and foliage can serve many purposes in the garden. The cool pale blue flowers knit a garden together. They work in much the same way as white does but in a more subtle way. They are restful to the eye and calm the mind. Mix pale blue, silvery green, gray and lavender together for a tranquil area. Since many of the early flowers squill, crocuses, chinadoxa and forget-me-nots are available in cool blues and lavenders this lends itself to an early spring combination. Remember too that many of the hostas have a blue tint. Shade intensifies the paler blue tints in both flowers and foliage, tints that tend to be washed out in bright sun. Silvery artemisia makes a superb background for these delicate color schemes.
Blue in any shade also works well with the colors opposite it on the color wheel. Directly opposite is the color orange. A planting of marigolds and ageratum will certainly spark your border! It also works well with reds, pinks and deep yellows for a hot color scheme. Blue can also act as a means of balancing an arrangement of electric colors such as vivid pink, magenta and chartreuse and bright reds. Esther and Linda searched last year for a color that would not disagree violently with the magenta phlox at the library. They found it an extremely difficult color to work with. Perhaps blue would have served.
In late summer and autumn the frosty shades of Russian sage can be mixed with the ornamental cabbages and kales for a late season rush. They work well with the browns of fall and as you can see in this picture of the Brady Street circle and they are spectacular with the yellow leaves. (Now if someone would just mow the grass).