Over the last few years, my sister-in-law's hybrid yellow irises have started producing purple flowers. Can you explain why?
—Louise Royce, Cuyahoga Falls, Ohio
Melinda: Cross-pollination or plant mutation can cause flower colors to change. The offspring, or seedlings, of a hybrid plant often look different than the parent plant. That's because as different irises exchange pollen, a new mix of genetic material enters the family tree. Mutations—which can be produced by weather, stress, pests or natural causes—can prompt a plant to suddenly develop a new flower color, leaf shape or some other unusual feature. Some hybrid colors simply aren't stable and often revert back to a more stable flower color.