When & Where to Plant :
For best results, dahlias should be planted from mid April through May for most areas. Ground temperature approx. 60 degrees. (exceptions will be hot climates). In general about the same time you would plant your vegetable garden. Dahlias need a sunny location to thrive. An area that receives at least 8 hours of direct sunlight is best. Less sun equals taller plants and less blooms. Exception for hot climates, they will need morning sunlight, afternoon shade.
Sunlight: Full sun
Soil: Ground should be warm, well drained at planting, and in an open sunny location. If you have a heavier soil, add in sand, peat moss or bagged steer manure to lighten and loosen the soil texture for better drainage. Bone meal is ideal at planting time, put a small handful in the hole and work in well before planting tuber.
PH level of your soil should be 6.5-7.0, slightly acidic. Lay the tuber horizontally 4-6 inch deep, about 18 to 24inch apart, and then cover with soil. DO NOT WATER TUBERS AFTER PLANTING!! Please wait to water until after the sprouts have appeared above the ground. The exception will be in hot climates, where they should be watered very lightly.
Water: Most areas have enough rain to fill dahlia water needs until the sprouts appear above the ground. After dahlias are established, a deep watering 2-3 times a week for at least 30 minutes with a sprinkler, more required during warmer dryer weather. Hotter climates will need to water more often as conditions require. Proper watering promotes proper blooming.
Temperature: If you plant your dahlias in the early spring, the cold soil hinders initial growth -- your soil needs to be warmer than 62 degrees Fahrenheit for tuber sprouting.
Fertilizer: Dahlias benefit from a low-nitrogen liquid fertilizer (similar to what you would use for vegetables) such as a 5-10-10 or 10-20-20. Fertilize after sprouting and then every 3 to 4 weeks from mid-summer until early Autumn. Do NOT over-fertilize, especially with nitrogen, or you risk small/no blooms, weak tubers, or rot.