The key to creating lush, large scale flower arrangements is a bit of structural deception. A large container is rigged with various floral supplies to anchor the stems in a position that leaves as much of the flower above the container as possible. This technique allows the flowers stems to be shown off to best advantage while maximizing the height, spread and dramatic impact of the arrangement.
Select a decorative waterproof container or vase ensuring that it is proportional with the flowers you have chosen for the arrangement. Plan for your container to be one-third to one-half the height of the flowers and foliage that will come out of or sit above it.
Fill the container with water soaked oasis floral foam or use floral tape to secure several blocks of the soaked foam into place in the container opening. Ensure the foam is deep enough that when the flower stem is plunged into the foam it does not come out the other side but comes to rest in the wet foam block.
Place your tallest flowers, greens and decorative twigs into the foam first to establish the basic structure of the arrangement. Place flowers in the foam either singly or in groups of three to create a more natural less, contrived look.
Keep arrangements that will be viewed from all sides roughly symmetrical and distribute each type of flower and green throughout the arrangement.
Place filler greens and flowers in the foam to bulk out the arrangement and disguise the foam and floral tape at the base of the arrangement.
Finish by placing your focus flowers in the most prominent positions in the arrangement using either bright accent flowers, more luxurious or costly flowers and/or larger flowers either singly or in groups of threes.