Like many other flowers, the mum's bloom time is directly related to the amount of daylight it receives. To force mums to bloom, you need to provide them with a short day and long night. Mums that have over 9½ hours of nighttime will flower. Keep mums inside until you've forced them to bloom, and then move them wherever you'd like to see their colorful flowers.
Set your mums on a level surface inside. Choose a room that has curtains, so you can block out the light when you need to.
Put in plant lights so you can control the simulated day length for your mums. Use 60-watt incandescent bulbs, placed 4 feet above your mum plants.
Set the lights on a timer to provide 14 hours of light, leaving you with 10 hours of night, which is enough to initiate bloom. Overlap this light with natural daylight. For example, setting the lights to remain on from 7 a.m. to 9 p.m. overlaps with the natural light outside.
Keep the mums inside while they are subjected to this schedule. Water the plants until the soil becomes saturated when they feel dry. Otherwise, confirm that your plant light works and provides 14 hours of simulated daylight.
Watch your plant for blooms. As the mums adapt to the long night, they will develop flower buds and flower.