Wash your vase thoroughly to make sure there is no bacteria inside. Use a vase that is wide and short, as this will help preserve the flowers longer.
Fill the vase only about three-quarters to 1 inch deep with cold water. Daisies soak up moisture through their stems and last longer in shallow water. For carnations, use 3 to 4 inches of water.
Cut 1/2 inch off the end of the stem on a 45-degree angle. Pluck or cut any leaves near the bottom of the stem. Trim the end of the stem every 3 to 4 days, or when you notice it is starting to turn brown and soggy.
Add a flower preservative to your vase made from 1 part sugar and 3 parts water. This will give the flowers nutrients similar to what they grew in.
Keep the flowers away from extreme heat and any fruits or vegetables. Store flowers in the refrigerator at night.