Pruning dahlias (Dahlia spp.) encourages bushy, dense growth with plenty of large flowers and gives you neat, tidy plants. You should also prune dahlias just before lifting and storing the bulbs over winter. Dahlias are hardy in U.S. Department of Agriculture plant hardiness zones 7 through 10, and feature a range of flower colors including pink, lavender, purple, yellow and white.
Before and after pruning dahlias, sterilize your pruning shears by wiping the blades with a cloth that was soaked in rubbing alcohol.
Pruning young dahlia plants helps prevent them from growing tall and leggy. When the plant stems have three or four pairs of leaves, or when the dahlias are about 1 foot tall, pinch out the central stems just above the top pairs of leaves with your fingers. Repeat the process on dahlias with final growing heights shorter than 3 to 6 feet when the plants reach 1 foot tall again. Taller-growing dahlias don't need a second pruning.
Removing flower buds is called disbudding, and this process encourages large blooms in dahlias. Disbudding the first flower buds to appear on dahlias encourages the plants to put their energy into growing leaves and stems, which support more flowers later.
Dahlias produce terminal flower buds at the stem tips, and side buds that grow on either side of the terminal buds or along the stems. The plants are usually about 15 inches tall when the first flower buds appear. Remove the first flower buds by pinching through the stems just behind the flower head. When more buds appear and the terminal buds are 1/4 inch wide, pinch off all the side buds.
To encourage repeat blooming in dahlias, prune the flowers as they fade. Pruning faded flowers prevents seed heads from forming, which often ends blooming. Pinch off dahlia flowers as soon as they begin to wilt. Remove the whole flower head, including the base where the seeds form. During the peak blooming period, you may need to deadhead dahlias once or twice a week.
Neatness and Tidiness
Dahlia leaves and stems can wilt, turn brown and become unsightly at any time during the growing season, but most often leaves and stems begin to die down toward the end of the season. Pruning away the unsightly leaves and stems keeps the plants looking good for as long as possible. Prune leaves and stems at their bases where they join the rest of the plant.
Prune dahlia stems before lifting and storing the bulbs over winter. Digging up dahlia bulbs and storing them during the winter protects the plants from harmful frosts. After the final frost, or toward the end of fall, prune dahlia stems to 3 to 4 inches above the soil surface.
Tie plant labels to the stems before digging up the plants, so you can identify the dahlia varieties when replanting them in spring.