Root geraniums by placing a 4-inch stem cutting in a sterile rooting mix. The rooting mix should include sand, perlite and peat. This type of mixture provides better success than attempting to root the plant in water.
Prepare the rooting pots by placing the sterile mix into 3-inch square pots. Water the mix to saturate it, and then allow the water to drain for about 30 minutes before taking the cutting.
Prior to taking the cutting, withhold water from the mother plant for two weeks, only giving it more water if the leaves begin to wilt. Use sharp clippers to cut a 3- to 4-inch cutting from a healthy, growing leaf stem. Do not take cuttings from the flowering stems.
Remove the leaves from the bottom 1 to 2 inches of the stem to expose the growth nodes. Press the stem into the prepared rooting mix up to the bottom remaining set of leaves.
Place the pot and cutting in a 1-gallon plastic bag to keep the cutting in a moist environment. Zip the bag closed, leaving a 1/2-inch opening to allow excess moisture to escape. Place the bag in a sunny location to encourage the geranium to grow. If the rooting mix feels dry to a 1-inch depth, add more water. After approximately five weeks, the plant should develop roots, and it is ready to transplant to a larger pot after another three weeks.