Mums are cool season plants. When grown naturally, they don't bloom until fall, when days shorten and temperatures cool. Plants in bloom now have been forced into bloom out of season by manipulating greenhouse conditions. When exposed to summer-like conditions outdoors, the flowers fade and deteriorate rather rapidly. Even in season, individual flowers don't last too long.

If still potted, try and keep out of direct sunlight and intense heat. Otherwise, just providing adequate water (but not excessive water) will keep the plants going as long as possible. Just don't expect the flowers to remain looking good for very long. Summer is not their best time of year :-)

Thank-you so much for the info!