I have mums that bloom really late each year. They just started now. I cut them down to 2 inches in July but they are still leggy.
When is the latest in New Jersey that I can cut them back without losing the flowers?
Answer
Some mums are just tall!! You have done your best to limit their size. Are they in full sun?? If the sun is less that full, the plants will stretch to try to get more sun. Early to mid July is the latest to cut back early to mid blooming mums in Philadelphia. You seem to have a late blooming variety, in which case you can probably pinch back again in late July or very early August.
You should be pinching back twice: once when you have three to four pairs of leaves and then later, end of July-early August, pinch back again. If the plants are in good sun, have good moisture and fertilizer, you should have good looking flowering plants in late fall.