Growing Outside: In colder areas where the bloom season may be shortened by cold weather, potted mums should be moved to a protected area. In cold locations, chrysanthemums growing in the ground can be potted up in September and moved into a sheltered area. They suffer little setback with this procedure, and you can have beautiful blooms through Thanksgiving!
Growing in high tunnels or cold frames for cut flower production : Recommend for cold zone 5-3. To help with blooming I recommend put a 30% shade cloth on the cold frame to help bud initiation August 1st. Make sure to have support netting these get 3 feet tall and will fall over with out it.
Pinching is recommended up till July first. Find more info on growing Chrysanthemums here