I hope you find the following information helpful in preserving your fresh flowers, whether from the florist, garden or local supermarket.
The Longest Lasting Flowers:
Rose ~ Vase life is 7 to 10 days, if you keep them in cool water. Buy roses with firm heads. Gently squeeze the bud and check for firmness. Always cut roses underwater (to avoid air pockets), then place in a water-filled vase.
Orchid ~ Vase life is 14 to 21 days. Trim Orchid stems and change their water everyday, or at least every second day. Remove all faded flowers.
Carnation ~Vase life is 14 to 21 days. Remove the leaves and petals at water level and below. White Carnations can be 'colored' by adding food coloring to the vase water. They slowly drink up the dyes and change color.
Lily ~ Vase life is 14 days. Always carefully remove the pollen to prevent staining, using gloves or paper towel. Remove faded blossoms to encourage re-blooming. However, beware of lilies like the "Star Gazer" which has a strong scent and can be over-powering in small rooms.
Gladiolas - Vase life is 14 days. Thin out and remove all the fading flowers as they die. Glads bloom from the bottom up so removing those spent blossoms doesn't leave an unattractive stem. I even like Glads when they're very short...perfect for tiny vases.
Chrysanthemum ~ Vase life 25 to 30 days, the longest of all cut flowers. Add clean water to the vase every day, trimming their stems about 1/8". Obvious, buy Mums with the longest stems so you'll have enough near the end of their life to still make a decent size bouquet. I've found that Spider Mums don't last very long, so I opt for the daisy-like ones, while violet and yellow Mums last longer than the white ones.
While those little packets of preservatives are handy, I like using my own liquid preservative. Here's the recipe:
1 teaspoon sugar
1 teaspoon bleach
2 teaspoons lemon juice
1 quart lukewarm water.