Answer: It's natural for geraniums to lose their older leaves. As the leaves die, they return food to the roots of the plants. Those leaves that are turning yellow, even though the veins are still green, are probably just going through the natural process of dying. The leaves with the red margins are indicating to you that they're unhappy in their present environment. Usually cold temperatures will cause this color change. Try to raise the nighttime temperature to 45F or even 50F degrees to make things more comfortable for your plants. Geraniums like lots of bright light and low relative humidity. They do best with plenty of air circulation around each plant, too. Why not pinch off the affected leaves and raise the nightime temperature a bit? Both these activities will help promote healthy new leaf growth.
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