When flowers begin to drop their petals, it is a signal that the plant is ready to set seed and, generally, to stop producing blooms. In nature, that is just fine since the primary goal of the plant is to produce seed to guarantee another generation and continuation of the species. However, in our gardens, we just want the plants to persist in producing flowers for as long as possible.
To keep the plants going, we gardeners have developed a technique called deadheading which will help us achieve our goal. It is not a very complicated procedure, just keep an eye on your plants and, when the blossoms begin to fade, gently snip them off. This will accomplish several things. First, it will trick the plant into “thinking” that it has not achieved its goal of seed production. Therefore, with stubborn persistence, it will usually develop more flowers for us to enjoy.
The other thing that deadheading accomplishes is that it prevents seed production. Many of the plants we grow in our gardens are hybrids. They are the result of cross-pollination which combines the genetic material from two different plants. When this is done under the trained eye of the plant hybridizer, the results are predictable for the plants or seeds we buy from the nursery. The next generation exhibits hybrid vigor and produces an outstanding set of flowers.
Unfortunately, if you save the seed from these plants or if they just fall to the ground in your garden, the results are not predicable. Some of the seeds from hybrids will “revert” to the parental types and produce plants that you may not recognize. This can be fun if you are experimenting and trying to find new varieties. But, if you want a homogeneous group of white flowered garden phlox from their seed, you will probably be disappointed. For example, named cultivars of garden phlox, Phlox paniculata, will often revert to common pinkish flowered wild types when seed is collected from a hybrid.
Deadheading your annuals i.e. bedding plants, is pretty straightforward. It will help to keep producing flowers into the cold of autumn. The goal with annuals is to keep them blooming and blooming from the time you put them in the ground in the spring until they are killed by the frost in the fall. Some of the new cultivar on the market have been chosen to keep flowering even without deadheading. The “Wave” petunias are an example of this advance. Unfortunately, many, many other annuals are not to this stage of development and still benefit from deadheading.
With perennials, it can be a little more complicated. Perennials are plants that live more than two years. Some of them like peonies, daylilies and hostas live for decades and decades. Deadheading these plants is meant to “clean them up” and to avoid letting them go to seed. In some cases, it will encourage some additional bloom but most perennials will limit themselves to their normal blooming season length even if you dead head them. A few will put out some additional blooms but they will not react like annuals.
A small group of perennials are called “short-lived” since individual plants may only live 4 or 5 years. Coreopsis, gaillardia, delphinium, primulas and similar plants do not have nearly the longevity of hostas or daylilies. In these cases, you may not want to deadhead them and allow them to self-seed.
By knowing your plants and understanding which ones come true from the seed, you can save yourself some money. Primroses are an example of a species that seems to reproduce pretty well from seed. Let them spawn seedlings and you won’t have to go to the store and buy more every few years.
Finally, we come to the case of deadheading roses. There are many different types of roses that are currently grown in the home garden. The vast majority of people only think of hybrid tea roses which are the ones you buy at the florist.
It is important to periodically deadhead hybrid tea roses (an some of the other types too) throughout the season. If they are allowed to form seed heads i.e. rose hips, they will stop flowering. So, once the flower begins to “shatter” which means that the petals begin to fall, it is time to deadhead that cane. Cut the cane down to the next 5 leaflet leaf. Snip the cane just a little above that leaf and a bud will form where the leaf stem enters the cane. From this a new little stem will form with a flower bud on the top.
Keep up this process throughout the summer to keep the hybrid tea in continuous bloom. Generally, in northern climates, it is good to stop deadheading roses around the first of August. Encouraging tender, new growth into the fall will not be beneficial to the plant since it will be zapped by frost. Of course, this rule does not apply to annuals which will be dead with the first heavy frost anyway.