Mums are traditionally pinched or sheared back every other week or so from early spring until about the middle of July. This treatment keeps the plants dense and bushy and causes them to produce many more blooming tips. It also delays blooming until later in the season. Some mums are earlier blooming than others, in spite of our best efforts. Cut the stems back to a lower-branching stem, preferably one with flower buds already forming.
Tip: Follow the stem down to where it forms a “V” and cut away the top with the spent flowers. The smaller stems that form the “V” will grow longer and produce new (slightly smaller) flowers.