Deadheading is the process of removing spent or fading flowers from a plant. It is usually done with scissors, garden shears or a knife. The purpose of deadheading is to encourage a plant to send out a second wave of flowers.
If you think about it--Flowers, while beautiful, are really just traffic cones or signal flares used to get the attention of pollinators and help in the transfer of pollen from one plant to another. After pollination occurs a plant begins the process of producing seeds and puts all of its energy into this task to assure that another generation plants are brought into the world.
Removing spent flowers,deadheading, before the seeds are produced tricks the plant into believing that it has failed so it sends our hormones that produce more flowers and tries to reproduce again. A long time ago humans discovered that deadheading was a way to fool mother nature and get a second set of flowers from cultivated plants.
The image above is of spent rose blooms that are commonly deadheaded. The yellow arrow is there to illustrate the forming of rose hips, the fruit of a rose plant, and the yellow line to show where one would remove the bloom in the process of deadheading.
When deadheading cut just below the bloom and try not to remove any foliage because energy that should be directed by the plant to form new flower buds will be diverted to growing foliage.
When to Deadhead
Deadhead when you want to extend the blooming time of your plant.
Deadhead to keep the plant and your garden free of spent flowers and petals that can be breeding grounds for pests and diseases.
If you have a plant that is weak either from disease or damage or newly planted. The forming and maturing of seeds takes a lot of energy if your plant isn't healthy allow it to focus its energy on growing foliage or roots and not seeds and fruits.
When NOT to Deadhead
Don't deadhead when you want to collect seeds to grow more plants. The second flush of flower may not set seeds and mature before the first frost or winter.
If part of the reason you garden is to attract wildlife, deadheading plants removes a food source the wildlife in your garden depends on.
Just to be clear: If you want to collect rose hips for use in either cooking, teas or crafts; leave the part I marked with the yellow arrow alone. It will turn the familiar red or orange color rose hips are known for, as it matures. I get asked about rose hips a lot and I think part of the confusion comes from the word "hips." I know when I first started in gardening and heard about rose hips I was looking for the hips on the side of the main stem. Yes, I admit I thought they would be hips like on a human.