Rose leaves often begin their life with a red tint, become green as the year progresses, and may then turn red again as fall approaches. Occasionally, they take on a reddish hue at unexpected times.
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Anthocyanins are natural pigments found in many plants, including roses. Over 300 different versions are known, and they produce the purple and red colors in rose leaves, petals and hips. Anthocyanins are particularly prominent in new leaves in spring, causing them to be deep red or bronze colored. It is believed this gives the new leaves protection from UV rays.
Rose Rosette Disease
Reddening of the leaves may be produced by a viral disease known as rose rosette disease. This may cause leaves to turn red or dark purple, new shoots to be long and deformed, and leaves and clusters of branching stems to become deformed. There is no cure.
Rose leaves are green in summer because the main coloring chemical is chlorophyll, needed for photosynthesis. In winter there is less sunshine so less need for chlorophyll. As the chlorophyll disappears, the red anthocyanins once again become the main pigment on view.