Pinch plant stems in early spring when the plant reaches about 6 inches. Use pruners or your fingers to snip about one-half of the length of each stem about 1/4-inch above a set of leaves.
Pinch again in the same manner when the plants have grown another 5 or 6 inches. Likewise, you may pinch a third time, but not later than July 10. By midsummer, you should have a full, round plant that is thick with buds.
Remove buds throughout summer, leaving a dozen or so buds on the plant. By disbudding, the plant's growth will concentrate on the buds that remain, resulting in fewer, but larger, blooms.