Once mums have been cut, they will last seven to 10 days in a vase if cared for properly. Mums will last longer when stored in a cold room at night.
Mums should be cut right before the buds open all the way. Using a sharp knife or scissors, cut the stems a bit longer than needed so they can be recut after they've been conditioned. Quickly put the cut flowers in a bucket of warm water to keep them from wilting. To make them last as long as possible, add a preservative to the water. Add more water daily to maintain the level in the container, and replace the water if it gets cloudy.