Hello there. It's me, your geranium. You've noticed my leaves turning red, and I appreciate your concern. Let me explain from my perspective. One of the most common reasons for my change in color is my reaction to sunlight. Think of the red pigment (called anthocyanin) as my natural sunscreen. When I am exposed to intense, direct sunlight, especially during the hotter parts of the year, I produce more of this pigment to protect my chlorophyll—the vital molecule I use for photosynthesis—from getting damaged by the sun's powerful rays. It's my way of putting on a pair of sunglasses. If I've been moved to a sunnier location or the season has changed, this is likely the cause. It is generally not a sign of distress but rather a sign of my adaptation.
Just as the sun can trigger my red pigmentation, so can the cold. I am a tender perennial, which means I thrive in warm conditions and am sensitive to chills. When the temperatures drop, particularly cool nights in the late fall or early spring, I begin to slow down my production of chlorophyll. As the green pigment breaks down and isn't replaced as quickly, the underlying red anthocyanin pigments become more visible. This is the same process you see in deciduous trees during autumn. It is a natural physiological response to the changing environment and signals that I am entering a period of slower growth.
Sometimes, my red leaves are a more direct call for help regarding my care. If I am not receiving enough water, I can become stressed. This drought stress can trigger me to produce anthocyanins as a protective measure. Similarly, if I am lacking certain nutrients, particularly phosphorus, I may not be able to produce the energy and compounds I need to stay my lush green color. A phosphorus deficiency specifically interferes with my energy transfer systems, and one of the visual symptoms can be a purplish-red discoloration on my leaves, often starting at the edges or on the undersides. Please check my soil; I might be hungry.
The container I live in can also be a factor. If my roots have filled the pot and become pot-bound, they can become stressed and struggle to take up sufficient water and nutrients, even if you are providing them. This root stress manifests in my foliage, often as red or reddish-purple leaves. Additionally, the quality of my soil matters. If the soil is too compacted, has poor drainage, or has a pH that is too acidic or alkaline, it can lock up nutrients, making them unavailable to me. This can lead to deficiencies that show up as red discoloration, even if the nutrients are physically present in the soil.
