Most floral arrangements last 4-7 days or longer, depending on the flowers used and the care they receive. The Society of American Florists provides these tips for longer-lasting, more vibrant flowers:

For floral arrangements

• Keep the vase filled (or floral foam soaked) with water containing a flower food provided by your florist. Flower foods make flowers last longer but it is important to follow the mixing directions on the flower food packet. Most packets are to be mixed with either a pint or a quart of water. Flower foods should not be diluted with more water than is specified on the packet.
• If the flower food solution becomes cloudy, replace it entirely with properly mixed flower food solution. If possible, re-cut stems by removing one to two inches with a sharp knife. Be sure to use a sharp knife or clippers that will not crush the stems. Immediately place the stems into solution.
• Keep flowers in a cool spot (65 to 72 degrees Fahrenheit), away from direct sunlight, heating or cooling vents, directly under ceiling fans, or on top of televisions or radiators. (Appliances like televisions give off heat, which causes flowers to dehydrate.) Most flowers will last longer under cool conditions.

For loose bunches or boxed flowers

• Keep your flowers in a cool place until you can get them in a flower food solution. Don't forget how important it is to follow the mixing directions on the flower food packet.
• Fill a clean (washed with a detergent or antibacterial cleaning solution), deep vase with water and add a flower food from your florist.
• Remove leaves that will be below the waterline. Leaves in water will promote bacterial microbial growth that may limit water uptake by the flower.
• Re-cut stems by removing one to two inches with a sharp knife. Place the flowers in the vase solution you've prepared.

Selecting Flowers

• When selecting flowers, look for flowers with upright, firm petals and buds beginning to open. Yellow, spotted or drooping leaves are signs of age.
• When using woody stems and branches (such as quince, forsythia or lilac), cut the stem with sharp pruning shears. Place them in warm water containing fresh flower food to promote flower opening.