Carnations are one of the most popular cut flowers, partly because they are inexpensive, but also because they last longer in a vase than many other blooms. Without any additional care, carnations may last seven to 10 days in a vase, but with added attention, you can have your cut carnations last two or more weeks.
Trim about 1 inch of stem off the bottom of each carnation, using a sharp scissors or a knife, every two to three days. Cuts should at a 45-degree angle to allow as much water uptake into the stem as possible. At the same time, trim off any leaves of the carnation that will be submerged under water in your vase.
Keep the water in your vase of carnations clean and full. Change the water in your vase every day, or every other day. Check to make sure all the stems are submerged into the water at all times. You may add floral preservative to your water or 1/4 tsp. of boric acid to one quart of water to further extend the life of your carnations.
Place your bouquet of carnations away from direct sunlight and heat. Carnations prefer a cooler atmosphere and will live longer if kept cooler. Move your carnations to a cool, 40- to 50-degree Fahrenheit area overnight to add days to your carnation life.
Ruffle the petals of your carnations, gently, every few days. By ruffling the petals you are stimulating the flower to take up more water and, thus, live longer.