Deadheading is a popular horticultural term meaning to remove dead or dying flowers from a plant. It may seem rather tedious to cut off every individual expiring flower on all your plants. Why do gardeners do this? The answer is two-fold. The first reason, the obvious one, is that dead flowers left on a plant look really unattractive. The second reason is that deadheading promotes further flowering.
Flowers are reproductive structures on plants that are a means to an end – flowers will eventually produce seeds, if left to go to that point. Producing seeds is expensive to a plant in the sense that it consumes a lot of a plant’s energy and resources. By removing expiring flowers you prevent the plant from spending its energy on seed production. With this burden removed, a plant often goes back to making more flowers in order to replace the seeds of the flower you just removed. This process keeps plants on their toes – they have to keep making more and more flowers for the seeds you keep removing.
Deadheading is a practice I use almost exclusively with perennial flowers. Annuals will generally produce extensively anyway, so it’s most useful when dealing with perennials. (For more information see the article on perennials vs. annuals.) The picture at right is a type of salvia that will bloom continually throughout the summer and fall if it is deadheaded, especially if the deadheading is alternated. If half the blooms are removed before they even bloom, a salvia will begin to produce the first half again while the second half blooms, and the salvia plant will alternately have half its flowers in bloom during the whole growing season.
If you’re actually interested in getting the seeds from your plants then allow the last flowers of the season to produce seeds and wait to harvest them until the flowers are completely matured.