if you are over feeding it it will produce lots of leaf. They also need lots of sunlight too. Not a true climber though.

I'd like to see a photograph of this "climbing geranium", as I'm pretty sure there's no such thing, so I'm wondering what it actually is.

its a tall variety. bit like 'climbing fuchsia'. i googled it to be honest as I was [am] sceptical. there is one particular nursery that provides them in particular.

Okay, googled it myself - Guest, where is yours growing and what, if anything, are you feeding it with?

I bought one last year and it was beautiful. I brought it in for the winter as they are not hardy but it was not happy! It tried very hard to die but I took some cuttings a few weeks ago and they are growing beautifully indoors.
I'd be interested in info on care too.
Mine was in a multi-purpose with added JI and some slow release food pellets.
They don't 'climb', the stems need tying to canes but they do get tall.