Cut carnations will typically last from 7 to 14 days with proper care. A carnation is a herbaceous perennial, meaning that when it is planted in the ground, it will last for at least 2 years.
To make cut carnations last longer, it is recommended to put them in room temperature water with the addition of flower food. A mixture consisting of a teaspoon of sugar, a teaspoon of lemon juice and a few drops of bleach dissolved into in 4 cups of water can be used in place of flower food if none is available.
The flowers should be cut at a slant, and any dying leaves should be removed. To help carnations last longer than a week, the water should be changed and the stems re-cut.