Here are some suggestions on how to root geranium slips to avoid rotting. Post your own techniques below.
When rooting geraniums: break off (or cut off with a sterilized knife at a 45 degree angle) just under a leaf joint. Let it sit for 3 hours to let the tip dry and seal itself off, very important! Then put in a glass of water and wait for 2 - 3 weeks for roots to develop.
Or, let it sit to dry and then dip in water to barely wet tip and then into rooting hormone and then plant in moist sterilized soil.
Geraniums don't like much water. Plant them in sandy soil in pots. Keep in the shade, and when they seem to have new leaves and growing, put them in the sun, with a little shade part of the day.
I've always just broke a piece off and stuck it back in the pot with the mama plant and left it until it was big enough to transplant. I very seldom fertitlize mine and they seem to bloom all the time. They were even blooming one year when we had snow. They stay in the sun most of the time and they are beautiful. I live in the Florida Panhandle.
I just break off a piece with flowers, leaves and stem, plant it in a pot, water, and voila!, it grows. Geraniums are so hearty they are hard to kill. I have a geranium from my grandmother's house from thirty years ago and from my mom's house ten years ago. They are doing great. I have taken pieces from them both and planted in smaller pots placed up and down my front steps. Looks great. I say try what you want to do and see for yourself.