Dahlias are exquisite plants, producing brilliantly colored blooms up to 12 inches in diameter. Unfortunately, dahlias are not winter-hardy, so growers in all but the warmest climates typically have to wait until spring to plant the tubers. If you'd like to get a head start on growing dahlias before the season's last frost, it's easy to plant the young tubers indoors as you wait for the winter freeze to pass. You'll bring some springtime greenery into your home and you'll be able to enjoy dahlia's first blooms several weeks earlier than usual.
Starting dahlias indoors
Dahlia tubers should be planted indoors about six weeks before the last expected frost. Plant them a few inches deep in a soil-free potting mix and place them in a sunny window or under grow lights. The room where they grow should be kept above 60 degrees F. Maintain an evenly moist potting mix but never allow the medium to become soggy or you'll risk letting your dahlias rot. If your plants grow taller than 12 inches, pinch them back before transplanting them to an outdoor garden. If you notice yellowing or browning leaves on your young plants, pinch off the lower sets of leaves; they may be obstructing air flow and allowing the plant to remain too moist.
Moving the dahlias outdoors
When the danger of frost has passed and the ground is around 60 degrees F, move the dahlia pots outside and let them gradually acclimate to the new environment: Place pots in a shady area of the yard for several days before moving them to an area with partial sun. Then give them a few days in full sun before planting your dahlias in the ground. Plant them in a location with full sun and well-drained soil, adding a handful of bone meal to the soil around each tuber. Give the plants enough water to keep the soil moist for one to two weeks or until they're well-established. Then care for them as you would any other in-ground dahlias.