From a botanical perspective, the color of a peony flower (genus *Paeonia*) is primarily determined by the presence and combination of specific pigments within the petals' cells. The three major classes of pigments are anthocyanins (which produce red, purple, and magenta hues), carotenoids (responsible for yellows and oranges), and flavonoids (which can create pale yellows and ivories, often working in concert with other pigments). The specific pH of the cellular environment can further influence the shade, making a red appear more crimson or more pink. It is crucial to understand that these colors are not arbitrary; they are a result of the plant's genetic makeup, developed through evolution and selective breeding to attract specific pollinators and ensure reproductive success.
Red Peonies: The vibrant reds, as seen in varieties like 'Karl Rosenfield', are predominantly due to a high concentration of anthocyanin pigments. These pigments are synthesized in the plant through specific biochemical pathways, and their intense color is often a sign of a healthy, well-nourished plant with ample sun exposure, which fuels the pigment production.
Pink Peonies: Pink varieties, such as 'Sarah Bernhardt', also rely on anthocyanins but at different concentrations or types than their red counterparts. The lighter shade is often a result of a lower pigment density or the presence of reflective compounds that dilute the color's intensity, giving the soft, blushing appearance so highly prized in gardens.
White Peonies: The pristine white of a peony like 'Duchesse de Nemours' is typically the result of an absence or near-absence of anthocyanins and carotenoids. Instead, the petals are filled with colourless flavonoids or other compounds. What we perceive as pure white is actually the light being scattered by intercellular air spaces within the petal tissue itself.
The development of true yellow pigmentation in herbaceous peonies was a major breakthrough in horticulture, achieved by hybridizing the common herbaceous peony (*Paeonia lactiflora*) with the yellow tree peony (*Paeonia lutea*). These hybrids, known as intersectional or Itoh peonies, inherit carotenoid pigments from their tree peony parent. This introduces the yellow, gold, and orange tones not naturally found in the standard herbaceous genetic pool. The sought-after coral shades, as in 'Coral Charm', are a complex interplay where underlying yellow carotenoid pigments are modified or overlaid with specific pink or red anthocyanins, creating a unique and transient color that often fades as the bloom matures.
While genetics dictate the potential color, several environmental and cultivation factors can influence its expression. Sunlight is a critical driver for anthocyanin production; a peony grown in deep shade may produce blooms that are paler than expected. Soil pH can also play a subtle role, particularly for colors involving anthocyanins, which can shift toward blue in more alkaline conditions or red in acidic ones, though the effect is less dramatic than in hydrangeas. Furthermore, the age of the bloom affects color; many peonies change shade as they open and senesce, with corals often fading to ivory and deep reds softening to lighter pink.
