(Image credit: Gumpanat)

Cosmos produce a delightful array of colored blooms from pink and white to yellow, red, and even brown. These pretty annuals produce prolifically, especially if you know how and when to cut back and pinch. Cutting cosmos will give you new flowers for the entire growing season as well as blooms for floral arrangements. 

Why Pinch Cosmos? 

Pinching back and deadheading aren’t exactly the same thing, but your annual cosmos benefit from both. The main reason to pinch back any plant is to promote new growth. Doing so stimulates new growth and a bushier, denser shape. 

Pinching is a simple type of pruning. It refers to picking off new growth on plants. You can use your fingers, hence the term pinching, or sharp shears. For thin, delicate stems, finger pinching is adequate. If stems are a little tougher, use shears to get a clean cut that minimizes infection or disease risk. 

The goal is to pinch off a stem just under a pair of leaves. There are two nodes here, and when you remove the top part of the stem, two new ones will grow from those nodes. Where you had one stem, you’ll now get two branching off at that point and a bushy, fuller plant. 

Pinching back in some plants also stimulate additional flower production. Not all plants respond this way, but cosmos do. Start cutting back cosmos early in the growing season and continue to do it regularly, and they will reward you with abundant flowers. 

How to Deadhead Cosmos for Continuous Blooming

Deadheading will also give you more flowers throughout the season. To deadhead means to remove spent blooms. As you see cosmos flowers start to fade, pinch or cut them back. 

The life cycle of a flowering plant ends in setting seeds. By removing the spent blooms, you set the cycle back and trick the plant into creating more flowers so it can get back to seed setting. 

When you see a fading cosmos flower, cut it back down to the next bud. If there are no buds, you can cut it back to the next set of leaves. If the stem is bare, cut it back all the way to the base of the plant. 

It’s best to start pinching and deadheading cosmos early. If you get behind, you can trim back the entire plant by about one-third when most of the flowers have begun fading. If it’s not too late in the season, this will give you a new burst of growth and blooms. 

Mary Ellen Ellis

Mary Ellen Ellis has been gardening for over 20 years. With degrees in Chemistry and Biology, Mary Ellen's specialties are flowers, native plants, and herbs.