Cosmos adds bright color to the summer flower bed with relatively little care, but once the flowers begin to die, the plant itself is nothing more than background filler. Plants produce flowers so that they will make seeds, and cosmos spent flowers are where the seed production happens. If the bloom is removed, the plant tries to make another flower to start the process all over again. Deadheading cosmos after the blooms start to fade will rejuvenate the plant and cause it to bloom over and over again, up until the autumn frost.
Reasons for Picking off Faded Cosmos Blossoms
Should you deadhead cosmos? The flowers are so small it seems like it may be more trouble than it’s worth, but there are ways to make the job go quicker. Instead of nipping off individual flowers with a thumbnail like you might do with a marigold or petunia, use an inexpensive pair of scissors to cut multiple blooms at the same time.
Cosmos is among the easiest of flowers to naturalize in your garden, which means when it goes to seed it will grow wildly anywhere it can reach. Picking off faded cosmos flowers before they go to seed will prevent the plant from spreading throughout the flower beds and keep your landscaping design in check.
How to Deadhead Cosmos
For flower beds with large amounts of cosmos plants, the best way in how to deadhead cosmos is by cutting back the entire group of plants at once. Wait until most of the blossoms on the plant has begun to die back, then use a pair of grass clippers or handheld hedge trimmers to shave back the entire plant.
You’ll encourage these plants to grow in bushier and thicker, while starting the entire flowering process all over again. In a couple of weeks your cosmos will be covered in a fresh batch of blooms.