Seasoned gardeners call it "dead heading". It sounds brutal but it's a very plant friendly practice of cutting off the old blooms to extend the life of annual flowers. Removing the faded blossoms sort of fools the plants into producing more flowers by delaying seed production.
With most plants it's just a matter of cutting off or other wise removing the individual flowers. Use your finger nails to pinch off petunia (pictured), dianthus, marigold or pansy blossoms. Some like geraniums and gerbera can simply have the blossoms snapped off - stems and all. With snapdragons, salvia and delphinium that grow the longer stems of blooms pruners are usually needed to do the trimming.
Many plants that produce lots of blooms also become lanky and overgrown. If you have a pot of petunias, impatiens, begonias or coleus you may need to periodically trim back the tips. Some times it means removing six inches or more of old flowers, seed pods and stems to renew the more compact growth habit. The new growth normally resumes in just a matter of a week or two.
- Feed in ground plantings every 3 to 4 weeks with a general garden fertilizer; feed container plantings every other week.
- Water when the surface soil begins to dry to the touch.
- Maintain an inch to two of mulch over the soil surface of in ground plantings to stretch the time between waterings.
- Control leaf chewing insects and mites with natural sprays available from local garden centers.
- Remove declining plants to prevent stem and root rot organisms from becoming established in the soil.
- Replant with new seasonal annuals as needed.