Select an archway for the event. These may be rented from event rental stores. Most are made of metal or wire and they are designed to install easily. To decorate the arch before the event, make sure to assemble the arch in advance.
Measure to the center of the top of the arch and twist a wire around the frame for reference. Unwind silk vines that you will use as a base for the arrangements. Silk vines come in many plant shapes and sizes. Select larger leaves if your arch is very tall, medium for a 10-foot-high arch and smaller leaves for short archways.
Find the center of the first vine and position it at the top center of the arch. Attach the vine to the archway with floral wire. Decide if your archway will be viewable from all sides or only from the front. You can sometimes save money by using more plants on the side that will be photographed. If you want a more balanced look, place the vines evenly.
Wind the vines so they drape every 1 to 2 feet along the archway. Vines have natural tapered ends that will reduce to one leaf. Untangle the vines and place each by bending and shaping the vine wires. Use floral wire to adjust vines that do not have a metal wire core to bend.
Position larger silk leaves at the center and ends of the arch. The arrangement should be large and full at the center and taper down toward the sides. Between these three large floral arrangements, scatter a few flowers, leaves and filler plants.
Place your most important flowers in the center of the arrangement and back the flowers with leaves for contrast to make them easier to see from below. Arrange the flowers with the largest at the top and front, tapering down to smaller flowers down the sides of the arch. At the base of the arrangements use smaller flower heads and follow the draping of the vines with the flower heads.
Secure your draping flowers with floral wire and hide the wires with florist's tape. At the corners where the vines may wrap down the archway posts, you can add more arrangements of draped flowers. Use the backdrop of the vines to highlight the flowers. Add filler flowers to make the large arrangements more full and to add depth to the vine sections.