I heard that if more than 1 geranium cutting is rooted in the same pot, that eventually they will kill each other. Is this true?
Nope - i have a few small pots with 2 geraniums in each that are doing fine. But, i reckon they would do better with a separate pot each.
I usually stick about 5+ cuttings in in a pot until they develop roots, and then transplant them into separate pots.
So i doubt that 2 cuttings in the same pot will kill each other, but they will certainly compete a bit.
In order to save space I have sucessfully rooted several Pelargonium cuttings in the same pot eg. five cuttings in a 5" half pot. Care is required when separating the rooted cutting so as not to damage the roots.