Why have my previously green pelargoniums developed red fringes to their leaves. They are still flowering but they look pretty poor. I didn't put them outside until June 1st.
Too cold at nights causes that.
Poor things got chilly - as did we all these last few cool weeks. They will come to no harm, the leaves that come through when (if) it gets warmer will be the normal colour for the plant in question.
I've got one or two like that, I googled for an answer and over watering seemed to be a common answer too - that fits with mine as we've had no cold nights since I planted them out.
The nights have been cold compared to the days, its the extreme change in temp that does it. Were they gradually hardened off.