Dahlias are easy to grow, but cannot take frost or survive cold winters.
To start, put Dahlias into pots with a growing mix indoors six weeks before planting in the garden, and you will get a jump on the season and earlier flowering.
Plant them into the garden only after you’re sure that frosty nights are over for the season. A good time is when you would normally plant tomatoes.
Sunlight: Dahlias need a sunny location and grow best with at least eight hours of direct sunlight, but in hot southern regions they prefer morning sun and afternoon shade.
Soil: The soil temperature should be around 15ºC. Dahlias prefer well drained soil, so if you have a heavier soil, add coarse sand, peat moss or bagged compost to improve soil texture for better drainage.
Planting depth: Plant dahlia tubers horizontally about 15 cm deep and 45 to 60 cm apart.
Water: Dahlia tubers don’t need to be watered after planting. Once the plants are growing for best blooming, water once or twice a week during hot, dry weather.
Fertilizer: Use a low nitrogen fertilizer, vegetable garden fertilizer is ideal. Apply fertilizer about four weeks after planting and repeat three to four weeks later. Do not overfeed.
Pinching: To encourage the growth of bushier plants with better stems for cutting, trim out the center shoot just above the third set of leaves.