There are many old wives tales in regards to extending the vase life of cut flowers. Such tactics as putting lemonade or sugar in the water, while loosely based on science, is not the best thing for your flowers and can actually do more harm than good.
The first step in ensuring you get the most out of your flowers is to start with a clean vase, scrub it with bleach or put it in the dishwasher. The important thing to remember is that bacteria is the enemy, the grunge left in the vase after your last bunch of flowers died will kill your flowers faster than anything else.
If you want to add something to the water the best option is to use the packets of cut flower preservative (flower food) that your florist gives you with the flowers. It is important however to closely follow the directions on the packet as adding too much, or not enough, can actually do more harm than good. The preservative contains sugar in a form that is readily absorbed by the flowers, and an antibacterial agent. If you do not have any cut flower preservative available, add a small drop of bleach to the water – the bleach kills the bacteria, keeping the water (and vase) clean.
Taking care of the flowers from the moment you receive them is paramount if you want to get the longest vase life from them. Do not leave the flowers out of water any longer than necessary, and keep them cool and away from direct sunlight. Before placing the flowers in the vase be sure to remove any leaves that will be below the water line – these will rot in the water and produce bacteria. At the last moment, using a sharp knife or scissors, cut about 2 – 3 cm off the end of the flower stems, on an angle and the put the flower in water. Lastly, be careful where you place the flowers. They should be kept cool, away from direct sunlight.
Every other day the water should be changed, rinse out the vase and add cut flower preservative or a drop of bleach each time, and again cutting the stems just before the flowers go back in to water.
If you follow these steps you will be sure to enjoy your flowers for much longer than you are used to.