Sometimes we select our flowers with a particular container in mind. Other times we go searching for a container after we have bought or been given a bouquet.
Container = 1/3 total height
Nothing looks worse than too few flowers in too large a vase, or tall flowers in a vase that is too short. The proportion is what matters. Some experts suggest that the height of the container should be one third the height of the total arrangement. The best thing is to experiment until the arrangement looks right to you.
If you are giving a New Year's Eve party and want to use a tall narrow necked container, you need only buy a few long-stemmed flowers. The neck of the vase will support the stems so that the flowers do not flop sideways.
If you use a wide necked container, more flowers are needed to fill the opening at the top of the vase or the stems will splay out in an awkward way instead of standing upright. If you have a wide necked short vase, long stemmed flowers must be cut shorter and the same length so they are massed to provide more impact.
If you use a very shallow bowl, cut the stems short enough that the heads are just above the rim. To stabilize stems use oasis foam or a pinhead holder.
The life of tall stemmed flowers can be prolonged by cutting the stems once they are past their prime and massing them in a lower container where it is not so obvious that they are beginning to droop.