Gardenia stems for rooting should be 5 to 6 inches long and taken from the tip of a branch. Strip the stem of leaves except for a few leaves on top.
Prepare the appropriate number of small-necked bottles, such as soda bottles, by cleaning them thoroughly. Fill them with lukewarm water to within an inch of the top.
Fold paper towels into eighths, and wrap the stems at about the halfway point with the paper towels, then insert the stems into the bottles, leaves up, using the paper towels as corks. The stems should be about 1 to 2 inches into the water.
Place the bottles in windows where they receive direct morning sunlight only. If the water evaporates, replace it as needed so the stems stay about 1 inch submerged.
The tiny white roots take about a month to develop. When they are ready, plant the gardenias in pots with sterile potting mix. Keep them well-watered, but not soaked. Set the potted plants in a shady area outdoors. After about 1 month, transplant them into your garden in a location with filtered sunlight.