How Does a Rose Bush Get Two Colors?
Most rose bushes have uniformly colored flowers. Some roses bushes, however, display flowers of several colors. Sometimes the flower itself is bicolored, sometimes a cluster of flowers displays a range of colors and sometimes the flowers on one branch are colored differently from those on the rest of the bush. This color variation happens in three major ways.
Flower Color Change
Many roses change color slightly as they age. When a rose bush has many flowers, including both newly opened and old blooms, at the same time, it often appears that the rose bush has several different colors of roses. Some roses have been bred to emphasize this color shift. Rosa Seven Sisters has clusters of roses in shades of pink, with the darkest ones carmine and the lightest ones a pale pink-mauve. Rosa Joseph’s Coat is another cultivar that presents a range of colors in its clusters of rose flowers, ranging from yellow through orange and crimson.
Other roses have been bred to have two colors in each flower. Typically, the inner petals are one color and the outer petals are a different color. The most famous cultivar of this type is probably Rosa Peace, with its yellow core and pink outer petals. A small number of roses have some petals that are bicolored and show color change from the center to the edge of the flower. Rosa Dream Come True, an award-winning bicolor rose, is yellow blushed with deep, ruby red.
Roses can be grown from cuttings and from seed, but most roses sold commercially are grafted. This means that a cutting from the preferred cultivar is joined to another rose, typically one that is older and has good root hardiness. The rose bush will bloom with flowers the shape and color of the cultivar. Sometimes, however, the original bush grows a new branch, and the flowers on the new branch will look like the blooms of the original rose. Theoretically, it would be possible to graft roses from two different cultivars to the same root stock, so that the rose bush would bloom in two different colors.
Response to Growing Conditions
Like other flowering shrubs, roses respond to a variety of growing conditions. A change in light, water or soil nutrients can cause a change in the color of the rose flower. Typically the change is subtle, but some rose bushes can change rather dramatically from one season to the next.
The "rainbow rose" sold by some florists will never be seen growing in a garden. The vivid colors are produced artificially after the flower is cut. Rosa Vendela is the cultivar grown for this process, and its flowers are naturally cream colored.
- “The Garden Primer”; Barbara Damrosch; 2008