*Scrub the vase and rinse with a mild bleach solution to kill bacteria, which clogs the stems and prevents water from reaching the buds.
*Cut flowers in the morning when moisture content is highest (flowers are 90 percent water). Recut stems at a 45-degree angle, under running water, using a sharp knife or clippers, not scissors, which can crush cells and block uptake of food and water.
*If the plant has a woody stem, such as hydrangea, smash the last inch or two and peel the bark to facilitate water absorption. Some flowers (including celosia, sunflower and zinnia) benefit when ends are scalded in boiling water or briefly held over a candle flame to retard the sap from oozing.
*Use tepid water (100 to 110 degrees) and change it every day or two. Remove any foliage that's below the water level and cut 1/2 inch from the stems every few days.
*Annual flowers with the longest vase life include: alstroemeria, aster, celosia, cosmos, gypsophila, lavatera, rudbeckia, scabiosa, snapdragon, statice, sunflower, yarrow, and zinnia, according to information on the Web site of the National Gardening Association.
*If you are using purchased flowers, include the packet of food. "They don't just throw them in for fun," said Lewin.