When you cut a flower you remove it from its life system. It can no longer get food or fight off bacteria. This is why florists give you a packet of what they call "flower food." The flower food provides the plant with nutrients as well as an agent that prohibits bacteria from growing in the water of your flower vase. If you are not given a packet of flower food, or if you pick your own flowers, you can use bleach to keep bacteria from forming in the water. This will preserve the life of your cut flowers.
Pour the water into your vase and allow it to reach room temperature. If you place your cut flowers in cold water it can shock them.
Add 2 tbsp. of lemon juice, 1/2 tsp. bleach, and 1 tbsp. of sugar to the water in the vase. Mix the ingredients up. These ingredients work the same way that the mix in the florists flower food packets do.
Cut your flower stems at a 45-degree angle. Set your cut flowers in the prepared water.
Make new "flower food" and snip the ends of your stems every three days. Changing the water will keep your flowers looking healthy and strong.