For centuries, people around the globe have searched for a true blue flower. Elusive and rare, it is seldom found in nature. Or, to put it another way, it is rarely perceived in nature. It all has to do with what each of us sees as true blue.
To find out why this is so, I signed up for an on-line lecture given by Brandon George, a grad student in public garden stewardship at Cornell Botanic Gardens. His research not only produced a great list of blue flowers, but also shed some (hint) light on the issue.
WHAT CONSTITUTES BLUE
So why is blue so rare in the plant world? For starters, I’ll ask you to refer to the color wheel below.
Blue is a primary color. On the visible color spectrum, it is located between green and violet. But that’s where things get murky. Take a look at the wheel. Some blues tend towards green, while others tend towards violet. Do all of these pigments merit the name blue?
Indeed, how does one determine what constitutes a true blue? This has turned out to be a problem for horticulturalists and growers the globe over. To address the issue, the Royal Horticultural Society (RHS) in 1966 created a chart by which you could match precise colors to flowers, fruits and other plants. Now in its 6th revised edition, the RHS Colour Chart is today the standard reference used by horticulturalists worldwide for communicating information about plants. It contains 920 colors.
Still, while the RHS Colour Chart helps differentiate among different tones of blue, it doesn’t explain why a true, pure blue remains so elusive. And here’s the surprise. While blue is a very prominent color on earth, it is rarely produced in nature. In fact, of all the 280,000 known species of flowering plants, only 10 percent are blue.
HOW PLANTS PRODUCE BLUE
It turns out that plants aren’t born blue. Instead, much like artists, they must mix naturally-occurring pigments to achieve their blue hue. The most common of these pigments are called anthocyanins. Anthocyanins are responsible for many colors, from orange and red to violet and blue. And they can vary according to soil pH, which indirectly impacts flower color.
Hydrangea macrophylla ‘Nikko Blue’
What we perceive as blue, then, is actually the result of reflected light from these anthocyanins. And just the tiniest tweak of metal ions in the soil can result in the same plant producing different blues. (Think blue hydrangeas, which are produced by adding acid to the soil.) Finding a true blue flower is pretty hard indeed.
WHEN PURPLE LOOKS BLUE
Even then, some of us may still see purple as blue. Deutan Color Blindness (do-tan) is an anomaly of the ‘M’ cone (Medium Wavelength Light) in which spectral sensitivity is shifted toward longer wavelengths. If you have it, you may experience confusion between colors such as purple and blue. Take a look at the photo below. Do you see purple and blue or just blue?
TRUE BLUE PRETENDERS
Nowadays, blue flowers are highly prized. As a result, growers are introducing more and more plants that are labelled as blue. But beware – many are not truly blue! To differentiate among cultivars, horticulturalists now use the term ‘true blue’ to indicate a more true blue pigment.
Take, for instance, the hardy geranium ‘Rozanne’, a popular choice for the perennial garden. Some growers list it as violet, others lists it as blue. How do you perceive it? To my eye, it tends towards purple. While my colleague sees it as blue.
Hardy geranium ‘Rozanne’/Photo: anniesannuals.com
Have you ever wondered why the same blue plant can look entirely different across catalogs? Just because a plant has blue in its name doesn’t necessarily mean it’s blue. Some growers manipulate photos to make plants appear more blue. While others use tricks of light. If you can’t see the plant in person, George recommends consulting user uploads rather than seller photos to get a better perspective on a plant’s true color.
TRUE BLUE FLOWERS
There is one plant family that typically produces the truest blue flowers in nature. Boraginaceae, also known as the forget-me-not family, includes more than 27,000 species. The plants of this family are frequently hairy and include such garden ornamentals as Virginia bluebell (Mertensia virginica), Lungwort (Pulmonaria), Forget-Me-Not (Myosotis) and Heliotrope (Heliotropium). Horticulturalists agree that these are indisputable blues, although changes in pH can induce color changes as the petals age.
Other indisputable blue flowers include Grape hyacinth (Muscari), Siberian squill (Scilla siberica) and Blue Drumstick (Allium caeruleum), in addition to pH-sensitive Hydrangea macrophylla, which in acidic soil (a pH below 6) will turn blue.
Blue Drumstick, Allium caeruleum
And don’t overlook the sky blue flowers of Brunnera macrophylla, Delphinium grandiflorum, and Plumbago cerastostigma, which are all great additions to the spring/summer border.
TRUE BLUE ANNUALS
Perennials not your thing? There are also some great almost-true blue annuals. Evolvulus ‘Blue My Mind’, is a dwarf morning glory with fuzzy, silvery-green foliage. It looks great in containers or windowboxes, where it will happily trail over the edge.
Other great true blue annuals include Plumbago auriculata (a very light blue), Love-In-A-Mist, and Gentian sage (Salvia patens), a tender perennial that has the deepest blue flowers you’ll find.
Gentian sage, Salvia patens
DESIGNING WITH BLUE
When working with blue, remember it is considered a cool color, so it will recede into the landscape. Consider bringing it forward to enjoy it and plant cultivars in mass for a stronger effect.
But a word of caution. Placing a lot of different ‘blues’ together will often cause some to look bluer than others (see below). To prevent this from happening, separate them out and plant them instead next to contrasting colors (such as orange or yellow), which will give the illusion of a brighter blue.
Blue or purple? Delphiniums growing in Dalat, Vietnam
For photos of my landscape designs, check out my Instagram at carole.herebydesign. I post seasonally from spring through late fall.