Calla lilies have soft, hollow stems that have to be treated gently as to not crush the delicate cell structure.
Cut the stems at a diagonal with a sharp knife. Scissors crush and squeeze stems, making water uptake difficult.
Start with larger stems at the top of the holder.
Angle the stems to the side, defining the final length of the upper part of your bouquet.
Work the stems gently into the foam, working it in with your thumb and forefinger rather than roughly pushing it in, which can sometimes split or crush the stem if you aren't careful.
Note the insertion lines and directions of the miniature stems.
The center callas need to be inserted straight in and slightly to the right, giving depth to the final design. Cut these stems short and use smaller heads for the center if you can.
You can see how the center calla is flush against the foam, deeply seated into the middle of the bouquet.
From a side view, you can see how the flower heads have depth rather than a flattened look.