Buy all one type and color flower. Even if the flowers are carnations (which are typically one of the most inexpensive) they instantly look more chic than an arrangement. Opting for a single color can also cost less than an arrangement. Some of my favorites are peonies, hydrangeas, ranunculus, carnations and sunflowers.
Make them last: By cutting the stem at a slight angle, the water is absorbed better and the flowers typically last longer. Also, be sure to trim the stems a little after a few days.
Add water often: When recutting, be sure to add fresh water. This will extend the life of your arrangement.
Check for mark downs: Okay now this is a tip from my roomie: Many farmer's markets and grocery stores have marked down flowers that easily last a solid week or two. Just be sure to use the little packet they usually come with.
Feed your blooms! Be sure to use the 'flower food' to make them last as long as possible. I once had flowers last and look great for an entire month!
Placement: Don't put your cut flowers directly in the sun or too close to air/heating vents. I like to place mine in places that I spend the most time and where I will see them as soon as I awake in the morning.
Enjoy!!
