Your plant's haircut, so it can grow better
Many shrubs and vines will outgrow their containers quickly unless they are pruned back regularly. Pruning is generally reserved for perennials with woody stems - but even many fresh green annuals respond well to proper pinching and shaping.
Any major pruning should be done just after a plant finishes flowering, or just before a new growth period, to direct the plant's energy into strong, healthy shoots and abundant blooms. All dead or straggly stems should be cut first, along with any suckers (shoots growing from the rootstock). Stems growing inward toward the center of the plant should also be cut to allow air and light into the plant's center.
Use sharp shears to make strong, clean cuts without ragged edges. When pruning, cut off the branch as close to (flush with) the main stem as possible. Partial stems should be cut about a quarter inch above a bud, at an angle, to let any moisture drain away. A perpendicular cut may cause the stem to die back. Your plants will thank you for the "new do" with strong stems and healthy blooms.