Fresh flowers can last longer whether from your garden or the florist. Cut flowers in the morning before the temperatures rise. Use a sharp knife or scissors so stems aren't crushed. Keep flowers in a bucket full of water as you cut. Condition the flowers, whether store bought or fresh from your garden, by placing them in a bucket of ice water. Remove any leaves that will be underwater when arranged.
Use Clean Containers
Scrub the bucket you use as you cut the flowers and the vase for the final arrangement with a solution of 1 tbsp of laundry bleach to 1 quart of water. Rinse well. Every three or four days, remove the flowers from the vase and rinse the vase with additional bleach water. Rinse with clear water. Fill the vase with ice water and replace the flowers.
Soak the Foam
If the flowers are in floral foam, removing the flowers to recut the stems ruins the arrangement. In that case, every two or three days, tip the container to drain out as much water as possible. Fill the sink with ice water, and plunge the container into the sink. Let it sit in the sink full of ice water for 15 minutes.
Recut the Stems
Flowers draw up water through the cells in the stems. Those cells eventually get clogged and die. Recutting the stems exposes fresh cells and allows the flowers to stay fresh longer. Cut the stems with sharp scissors or a knife. If possible, cut the stems underwater so air doesn't get into the stems and block the water flow. Recut the stems every two or three days.
Fresh Ice Water
Change the water daily. Remove the flowers, and dump the old water out of the vase. Rinse the vase and refill it with ice water. Replace the flowers.
Mist with Water
Mist the flowers with a fine spray of water every day. If the vase is placed on fine furniture, move it to the kitchen to mist. Since the water should be changed everyday, do the misting at the same time.
Where you place the flowers has a lot to do with how fresh they stay. Putting the flowers in front of a hot window or under the heating vent will cause the flowers to fade faster. Tropical flowers, such as orchids, don't do well with cold breezes or near an air conditioning vent.