Gardenias are soft wood shrubs beloved for their fragrant flowers and deeply glossy foliage. They can readily be propagated by fresh stem cuttings in either a solid planting medium or in water. While a moist, easy draining planting medium such as a mixture of sharp sand and peat moss is recommended by the University of Vermont, rooting with water alone also works effectively.
Harvest a six-inch-long stem from your gardenia shrub with clean sharp secateurs. Strip off all of the leaves on the lower portion of the stem and leave two leaflets remaining near the top.
Prepare a rooting container by filling a clean, clear glass or plastic bottle with tepid water all the way up leaving just an inch or so of free space in the neck of the bottle.
Fold a fresh paper towel lengthwise into eighths and wrap the stem cutting roughly at its midpoint with the narrow paper towel strip.
Slide the wrapped stem into the bottle leaf side up as a cork in the bottle, ensuring that the bottom of the stem is submerged in the water by at least 3/4 inch but not more than 2 inches.
Place the bottle in a window with direct morning sun but no direct midday or afternoon sun, as this will overheat the water. Refill the water as needed to maintain contact with the bottom of the stem.
Allow the roots to develop over the ensuing month. After a month and a small mass of delicate white roots has formed, pot the cutting up in fresh, sterile and lightweight potting mix. Water in well and keep the soil very moist but not soaking wet monitoring it every other day. Site the plant in a shady protected location with only dappled sunlight, if any.
Move the young potted plant out of the shade and into an exposure with morning sun after two to three weeks. Leave in place for a month before planting out into the garden soil in a filtered sun location.