Fill a wide vase with lukewarm water. Dissolve a floral preservative in the water, following the instructions on the envelope.
Strip the leaves from the calla and gerbera flower stems. Place the stems in the prepared vase so the flowers remain hydrated during the bouquet-making process.
Gather three gerbera stems together. Arrange the stems so the flowers face outward.
Add three calla lilies to the bouquet. Place the lilies so they sit between the gerbera, flowers but slightly lower than the tops of the gerbera blossoms, creating a rounded appearance.
Hold the stems tightly in your hand so the bouquet retains its shape and arrangement. Slip a rubber band around the stems to hold the stems together.
Slide the stems of smaller gerbera blooms through the rubber band. Arrange these blossoms so the flowers sit against the bottom of the lily flowers, forming a border around the bottom of the bouquet. Use five to seven smaller blooms for this tier, depending on the size of the daisies.
Wrap a 2-inch-wide cloth ribbon around the stems, 2 inches down from the bottom of the lowest tier of flowers. Tie the ribbon into a bow. Slip the rubber band off the stems.
Trim the bottom of the stems with a sharp knife so the stems are even. Place the bouquet back in the vase until you are ready to use it.