Deadheading a Dahlia

A dahlia in bloom.

Encouraging new blooms on your decorative outdoor flowers such as your dahlia, marigold, and petunia plants is most easily done by a process known as deadheading. Deadheading is the name for removing the petals and seeds of a flower as soon as it fades. When you do this, you will find that your flowers continue to bloom throughout the entire growing season. In fact, on flowers that are not deadheaded, the blooming won’t continue after one instance. That is because leaving the dying flowers on the plant prevents it from continuing to produce new flowers. Deadheading your dahlia conserves its energy for the replenishment of beauty that it would otherwise spend on making seeds.

When to Deadhead

Deadheading should be done as soon as you see pollen appearing on the plant (other signs include a shriveled appearance, fading petal color, and brown petal tips). When you deadhead a dahlia, new blooms are encouraged because the plant does not spend its energy producing seeds. Not to waste the cut dahlia, bring it indoors and make an attractive flower display. When you trim a fading dahlia always follow the flower stem back to where it meets the main stem of the plant and cut here. If you notice new flower buds developing below the old, only cut back to the first new bud.

TIP: Rachel Klein, our gardening expert, suggests: "Deadheading is best performed after rain storms. The large blooms can easily fill with water or take a beating from the wind and will need to be removed."

Deadheading vs. Pinching Back

The difference between deadheading and pinching back is that you pinch a flower back before it blooms while deadheading occurs after the flower has bloomed. Pinching back a dahlia allows it to grow a little bushier than normal. It also promotes stronger and longer stems for cut flower arrangements. To pinch back your dahlia, cut the center shoot just above the third set of leaves, or keep the plant to a height of 18 to 20 inches tall. Both pinching back and deadheading are necessary pruning techniques that will help encourage the best possible growth from your outdoor flower garden.

Benefits of Deadheading

In addition to encouraging new blooms deadheading helps to keep your dahlias healthy. If your region is experiencing a dry spell, deadheading the dahlias is a good way to keep them safe from the excessive heat and lack of rainfall. Deadheading also maintains the general pleasant appearance of your garden. Deadheading dahlias—and other flowers—tells onlookers that you take pride in your garden and see to it that it does not go unattended.

TIP: Rachel adds: "If you want to use your deadheaded flowers for cut flower arrangements, the best time to cut the blooms is in the cool of the morning. Follow the flower stem back to where it meets the main stem, or to where it meets a developing bud, and cut the stem with a pair of sharp gardening shears. Snip the tip of the stem at a 30-degree angle."

Other Pruning Techniques

Another pruning technique common with dahlias is disbudding. Disbudding involves isolating the main bud by removing auxiliary buds that form as offshoots of the principal one (dahlia flowers grow in groups of three). It is the main center bud that will bloom into the beautiful flower, so it is best to save the flower’s energy for what has the best chance of blooming.

In order to encourage a continual appearance of new blooms, to protect the vulnerable flowers from a dry spell or heat wave and to keep up the overall appearance of your flower garden, deadheading your dahlias is both advisable and necessary.

TIP: If you're planning on using dahlias for a flower arrangement, Rachel points out that: "Some types of dahlia can grow very tall, and these long stems are perfect for flower arrangements. However, they are susceptible to bending or breaking. Insert three strong bamboo stakes around your dahlia and attach a few flower stems to each using garden ties, strips of nylon stocking, or dental floss. Tie the stems securely, but not too tight. This will promote healthy and safe stem growth."