Trim greenery from all but eight of the gardenia flowers with the stem cutter. Pull away any damaged outer leaves from all blooms.
Fill a bucket halfway with cool water. Place the stems inside until you are ready to assemble the bouquet.
Remove one gardenia flower stem at a time. Blot the stem dry with a paper towel. Hold one gardenia stem in your hand. Use the other hand to add three more stems to create a square shape.
Surround the square with more flowers to create a dome shape until you use all but the last eight gardenias with leaves. Insert a stephanotis bloom periodically between gardenia blossoms.
Insert the gardenia blooms with the leaves left on the stems at the bottom of the bouquet. The dark green, 2- to 3-inch-long and 1-inch-wide leaves characteristic of gardenias provide contrast with the white flowers.
Wrap green floral tape around the stems. Begin just below the blooms and work your way down to 2 inches from the end of the stems.
Insert crystal-tipped corsage pins into the tape-wrapped stems for decoration.
Set the bouquet in a bucket of cool water. Fill the bucket so just the ends of the stems sit in the water.
Trim the 2-inch section off the stems when you are ready to use the bouquet. Wrap the bouquet in tissue paper and place in the refrigerator. Gardenias are fragile flowers that last in water up to two days and in the refrigerator for one day. Prepare the bouquet up to one day before you need it.