Pruning Primer - Pinching
Pinching is like heading back but performed on stem tips of herbaceous annual and perennial plants. Pinching encourages bushy growth and more branches for flowering. To encourage bushiness, pinch back growing tips to just above the topmost leaf or pair of leaves before the flower buds have developed. This will cause new shoots to form in the leaf axils all along the whole stem.
To produce shorter herbaceous plants (annuals and perennials), pinch back the main stem by about a third when they reach one-half their mature height. For example, a plant that normally gets 3 ft (0.9 m) tall at maturity can be pinched back to 2 ft (0.6 m) tall when it is about 2.5 ft (0.8 m) tall. Pinch back herbaceous plants to just above a leaf or pair of leaves. Pinching back herbaceous annuals and perennials in this way reduces the need for staking.
Steve Christman 3/6/01; updated 12/26/03, 9/21/15