There are a few tricks you can use at home to enjoy your flowers longer. We do our best here to prepare them for a long vase life by adding small chlorine tablets into our pails before we even put flowers in them. This way the water is clean, and will prevent the stems from becoming moldy.
With our lisianthus, we pre-treat them with Chrysol plant food. This is essentially food for the flower, and once absorbed, they will last longer.
Once you get them home, remove all foliage from the part of the stem that is submerged. Cutting an inch of the stem will also allow for better water uptake. Changing the water on a regular basis and cutting the stems regularly will definitely increase their lifespan. Using these methods chrysanthemums can last up to one month, and Lisianthus up to three weeks.