Dahlia Flowers Growing Guide
You can start dahlias indoors before planting them out or plant them directly into the open ground after it has warmed up. After all danger of frost is past, plant them full sun and deep, fertile, moist but well-drained soil enriched with plenty of organic matter. Whether plants are already in leaf or not growing, set the roots horizontally 3″ -6″ below the soil surface. If already started, carefully break off the lowest leaves to encourage additional roots to form. Don’t cover unsprouted tuberous roots completely at planting time–gradually fill in the holes as the plants grow. After setting out each plant, immediately drive a sturdy stake 6″ from the growing point, especially for tall cultivars. Don’t wait until the plants are up and growing, or you may destroy the tuberous roots. Mulch thickly with pine needles, straw, or compost after plants are at least 6″ tall and the soil is warm. Water often and fertilize liberally throughout the summer with fish emulsion, manure tea, bonemeal, or other fertilizers not excessively high in nitrogen.
When plants are about 6″ -10″ tall, pinch out the center to promote branding and more flowers. You can pinch them again after they put out another 6″ of growth. Tie the shoots to the stake as they grow long enough. When the flower buds reach the size of a pea, remove the side buds to allow the center one to grow as large as possible for its type or leave the side buds on for more but smaller flowers.
- Landscape uses: Many of the shorter and medium-height dahlias make excellent additions to the late-summer and fall border. Taller dahlias can temporarily screen out an unpleasant view. They’re also colorful in front of a tall hedge (leave a few feet between the hedge and the dahlias). Or grow dahlias in a bed by themselves.
- Special hint: Dahlias are hardy in Zones 8-11 if the soil is well drained and not allowed to freeze; otherwise lift them for winter.
Pest & disease watch
Handpick slugs and snails when the plants are small, and apply soap sprays to control spider mites in summer. Corn stem borers may attack dahlias, so be on the lookout for wilting shoots and cut them back until you find the borer. Cucumber beetles and grasshoppers relish the flowers; control with pyrethrins. To help keep viruses from spreading; destroy immediately any plants that produce yellow-streaked, twisted leaves or stunted plants.