Tender perennials that produce long-lasting blooms on sturdy stems from midsummer to the first frost in fall, dahlias (Dahlia spp.) come in an extensive variety of sizes, shapes, forms and colors. Although dahlias thrive with a moderate level of care, deadheading is critical for dahlias to produce continual blooms. Otherwise, the plant determines the blooming season is over and begins to shut down and produce seeds instead of flowers. Deadheading also keeps the garden neat and helps prevent disease. Although dahlias are often grown as annuals, they are perennial in U.S. Department of Agriculture plant hardiness zones 8 through 10.
Remove the bloom, along with the stem, down to the next leaf or stem, as soon as it wilts. Don’t remove the bloom without a length of stem because you’ll have unsightly bare stems. You can pinch the stem with your fingernail or use clean, sharp pruners. Check dahlias at least once every five to seven days for dead flowers.
Discard spent flowers and stems. Don’t allow wilted bloom and leaves to pile at the base of the plant because debris often harbors pests and diseases.
Leave a few blooms on the plant at the end of the season if you want to save seeds for next year. Cut the dry, brown blooms and shake the seeds into a paper sack or envelope.