Keeping your plants in shape
Pinching can help your flowering plants keep their shape and not outgrow their containers. Pinching also makes plants bushier, which often means more blooms.
You'll want to cut the stem just above a set of leaves or new buds. Otherwise, it will take a while for your plant to grow back. The point of pinching is just taking a "pinch", not severely cutting back the plant.
You can snip the ends with garden shears or use your fingers. Pinching is best done in the early morning before stems start to wilt in the afternoon heat.
Pinching only works on bushy plants, not ones with a single stem. Some candidates for pinching:
Alpine Aster (Aster alpinus)
East Indies Aster (Aster tongolensis)
Florist's Chrysanthemum (Chrysanthemum morifolium)
Flossflower (Ageratum houstonianum)
Italian Aster (Aster amellus)
Lobelia (Lobelia erinus)
Petunia (Petunia hybrida)
Sage (Salvia officinalis)
Snapdragon (Antirrhinum majus)
Yarrow (Achillea tomentosa)
Be sure to stop pinching before the bloom season of the plant, or you could cut off buds before they get started.
Done with care, pinching your plants can be kind.