A true blue peony does not exist in nature. The vibrant colors of this popular flower, ranging from white to deep red, are limited by a fundamental biological constraint. Understanding the science of flower pigmentation reveals why breeders cannot simply cross existing peonies to achieve this elusive color, making the quest for a true blue peony a long-standing horticultural challenge.
The Biochemical Barrier to Blue
Flower color is determined by anthocyanins, flavonoids responsible for red, purple, and blue hues. The precise shade produced depends on the specific anthocyanin molecule synthesized, the acidity of the cell sap (vacuolar pH), and the presence of co-pigments. The bluest shades in flowers, such as in delphiniums and morning glories, are produced by the anthocyanin known as delphinidin.
Peonies are unable to synthesize delphinidin because they lack the necessary enzyme pathway. Specifically, they are missing the enzyme flavonoid 3′,5′-hydroxylase (F3’5’H), which is required to produce the precursor molecule for delphinidin. Without this enzyme, peony genetics limit their anthocyanin production to pigments like cyanidin, which results in red and pink colors.
Defining the Natural Peony Color Spectrum
Peonies offer a rich, wide color palette despite the absence of blue. The spectrum includes pure whites, creams, and pale blush pinks, along with vibrant corals and bright reds. Many varieties also display deep crimson and near-burgundy shades, which are created by high concentrations of red-based anthocyanins.
The closest natural colors to blue are the lavenders and purplish-mauves, such as ‘Lavender’ or ‘Purple Emperor’ varieties. These colors occur when red-based pigments are expressed in a specific cellular environment that shifts their hue toward the violet end of the spectrum. Though these varieties are often marketed as “violet” or “lavender,” their underlying pigment structure remains genetically red-based, distinguishing them from a true blue flower.
The Horticultural Quest for Blue
Traditional cross-breeding methods cannot introduce a gene entirely absent from the peony genome. This fundamental limitation means that hybridizers cannot simply cross a red peony with a purple one and expect a blue offspring. The only viable pathway to creating a true blue peony is through advanced molecular breeding techniques.
Scientists must employ genetic engineering, which involves isolating the F3’5’H gene from a blue-flowered plant and inserting it into the peony’s DNA. This process is complex, similar to the one that resulted in the creation of the genetically modified blue rose, which still leans toward a violet hue. While research is ongoing, no commercially available, genetically engineered blue peony has yet been released to the market.
Addressing the “Blue” Illusion
When a “blue peony” appears for sale, it is almost always a result of artificial manipulation or mislabeling. The most common technique is dyeing, where white or light-colored peonies are cut and placed in water treated with blue floral dye. The flower absorbs the colored water through its stem, resulting in artificially blue-edged petals.
Other instances of “blue” peonies are often the misrepresentation of deep lavender or purple cultivars through misleading photography and digital enhancement. The dark violet varieties can appear blue in certain lighting or when images are edited to heighten the color saturation. Consumers should be cautious of any peony advertised as true blue, recognizing that it is either dyed or a highly-saturated version of a naturally purple flower.