More than 2,000 years ago, Greeks used carnations in ceremonial crowns. Today, they are long-lasting cut flowers to grow, and you're most likely to find them used as filler in mixed bouquets, thanks to the fact that carnations are durable, affordable and available in basically every color of the rainbow. With proper care, cut carnations can maintain their color and appearance for as long as two weeks before they start to wilt.
Preparing Cut Carnations
Try to get a bouquet of cut carnations into water as soon as you get them home. (Even if you don't have time to cut the stems and arrange the flowers right away, place the entire bouquet in a vase with a few inches of water to keep them hydrated until you're ready to work with them.) When you are ready to arrange your cut carnations, fill a vase about two-thirds full with room-temperature water. Pour in the contents of the packet of flower food that came with the bouquet, or add your own homemade flower food (see below).
Cut the stem of each carnation on an angle using garden shears or clean kitchen scissors. This creates more surface area for water to be absorbed into the flower, extending the life of cut carnations. Try to keep the stems long enough to nearly reach the bottom of whatever vase or container you're using; you'll need to trim them again over the next few weeks, so keep as much length as possible for now.
Trim or pull off any leaves that will sit below the surface of the water, which can make the water cloudy and encourage bacteria growth. Finally, arrange the prepared carnations until you're happy with how they look.
Keeping Cut Carnations Fresh
Because carnations are quite hardy, they shouldn't require any special maintenance. Keep them fresh using the same strategies you'd use to care for any standard bouquet. This means changing the water every three days (or sooner if it appears cloudy) and adding new flower food each time. Trim the stems each time you change the water, cutting off just 1/4 inch or so from each stem.
Remember that cut flowers generally do best when they're kept away from heat and light. Place the vase in an area that doesn't get a lot of direct sunlight and isn't in the path of any HVAC vents. Keeping cut carnations cold will also help prolong their life. If you can spare the space, put the bouquet in the refrigerator each night.
Making Flower Food for Carnations
That mysterious powder that comes with a bouquet of flower food really isn't all that mysterious: It's basically a mixture of citric acid (to control the water's pH level), sugar (to feed the flowers) and bleach (to kill bacteria). Adding this flower food really can make a discernible difference in the longevity of your carnations, so try adding it every time you change the water. Considering that store-bought bouquets tend to come with just one packet, it's a good idea to know how to make your own flower food.
One option is to replicate the makeup of commercial flower food. After filling the vase with water, sprinkle in about 1 tablespoon of sugar, 2 tablespoons of lemon juice and 1/2 teaspoon of bleach. Leave out the bleach if you don't feel comfortable handling it.
Another option is to use a handy product that already combines citric acid and sugar: non-diet lemon-lime soda. Pour about 1/4 cup in with the water each time you change it. Again, adding 1/2 teaspoon of bleach is optional.