Although it sounds gruesome, "deadheading" annual and perennial flowers keeps your garden tidy, and does no harm to your plants.
The procedure is simple enough: merely remove spent flowers. Just look at those old, browning flowers on your geraniums. Snap them off, and you've instantly improved the look of your plant.
Most important, besides the immediate improvement from clearing away ragged petals, deadheading allows a plant to channel its energy into making more flowers rather than seeds. Annual plants live to make seeds.
Once that occurs, these plants slacken their efforts at making more flowers. Snapping off spent flowers before seeds form keeps marigolds, zinnias, and other annuals energetically pumping out new blossoms all summer long.
Even some perennial flowers, such as delphinium and Canterbury bells, put on a second show later in the season if their spent flower stalks are cut back right after their first show of the season is over.
You would have quite a time trying to cut off individual flowers or stalks from a plant such as sweet alyssum, an annual that forms a low growing mound completely showered with blossoms. The way to deadhead this plant is to shear the whole mound back with either grass or hedge shears after each flush of bloom. Shearing not only revitalizes the plant, promoting more blossoms, but also puts the plant back in place if it has sprawled out of bounds.
Other annuals that benefit from deadheading by shearing include nasturtium and petunia.
But don't go berserk with your shears trying to tidy up, because sometimes these trailing plants look best a bit unrestrained.
You might want to use your shears to keep sprawling perennials tidy even if the plants are not going to blossom again this season. Perennials whose appearances benefit from shearing include basket-of-gold, cottage pink, sea pink, edging candytuft, spike speedwell, and horned viola.
Whether they are annuals or perennials, sheared plants will appear stunned for a couple of days after the operation. However, good growing conditions soon have them happily lumbering along the ground and, in the case of annuals and some perennials, again flowering.
Besides sprucing up the appearance of the plant itself, deadheading also keeps a planting neat by preventing unwanted self-seeding in flowers that have the potential to become weedy. Religiously deadhead especially fecund plants such as feverfew, perennial phlox, and thick-leaf phlox.