Cutting off spent flower blooms, otherwise known as ‘deadheading,’ is necessary not only to keep your garden or landscape looking tidy, but to also encourage new blooms from plants that would otherwise be done blooming for the season.
Most plants produce flowers as part of their reproductive cycle. If their flowers are allowed to make seed, their lifecycle is finished and they will quit making blooms. If their flowers are not allowed to go to seed, they will generally send out more blooms until they're able to produce seed.
Keeping your flowering plants in a reproductive cycle by deadheading is a simple way to keep color and life in your garden for an extended period of time. Some perennials will even give you an entire second bloom at the end of the season that may last well through the fall; many types of roses do this.
A good reason to prevent certain perennials from going to seed is so that the seeds don’t spread and germinate outside of your plant’s designated area. If your perennials are left to seed, one gust of wind could cause a plant infestation. Also, seeds cross pollinated like this usually don't reproduce the same strain as the parent plant. If left unchecked, your prize beauties will eventually be choked out by a mix of undesirable, unrecognizable offspring of the parent plant.
Another reason for deadheading is to help keep your plants healthy and vigorous. Remember, they're trying to reproduce and are channeling energy. A lot of the plants energy goes to making seeds. So the energy that would otherwise be used for producing seed will be used for more growth and beautiful, flowering blooms.
There are numerous different perennials with different leaf and plant structures. This makes it difficult to put deadheading methods in a nutshell. However, depending on the types of plants you use and your reasons for pruning, there are different ways to go about it.
Cutting off individual flowers as soon as they start to fade or wilt is the simplest and most common method for most plant types regardless of mass, density, clusters, or size. However, some plant types that produce masses of blooms in mounds or clusters over the entire plant may take too much time to cut each individual flower, and if you're pruning to prevent seeding, it would require a lot of close attention.
If clusters or masses of blooms are growing on individual branched stems, you can cut back entire sections of faded flowers to the next branching and force new branches with new blooms. This will also help promote new blooms on lower branches.
In some instances of mass blooming perennials, cutting back the entire plant is the most efficient method. The plants themselves will come back just fine. You may even get an entire second blooming after a few weeks.
Deadheading will help keep your garden and landscape looking clean and neat, while at the same time promoting new blooms and maintaining vibrant color longer into the season.