For floral arrangements:
1) Keep the vase filled or floral foam soaked with warm water. Add fresh, warm water daily. If the water turns cloudy, replace it immediately. If possible, recut stems by removing one to two inches with a sharp knife. Do this under water. This allows the stems to draw in water instead of air.
2) Keep flowers in a cool spot (65 to 72 degrees Fahrenheit), away from direct sunlight, heating or cooling vents, directly under ceiling fans, or near radiators.
3) If a rose starts to wilt, remove it from the arrangement, and recut the stem under water. Submerge the entire rose in warm water. The rose should revive in one to two hours.
For loose stems:
1) If you can't get your flowers in a flower food solution right away, keep them in a cool place.
2) Fill a clean, deep vase with water and add the flower food obtained from your florist. Be sure to follow the directions on the package.
3) Remove leaves that will be below the waterline. Leaves in water will promote bacterial growth.
4) Recut stems under water with a sharp knife and place the flowers in the vase solution you've prepared. (Ward Upham)