How to grow dahlias

Dahlias are easy to grow, but cannot take frost or survive cold winters.

Pre-starting indoors until early May

To pre-start dahlia tubers yourself, put them 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.

Outdoor from mid May

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 or above 15ºC at planting time. Dahlias prefer well drained soil, so if you have a heavier soil, add coarse sand, peat moss or bagged manure to improve soil texture for better drainage.

Planting & caring

Planting depth: Plant dahlia tubers horizontally about 1 inches (2,5 cm) deep and 18 to 24 inches (45-60 cm) apart.
If you are going to stake your plants (larger types benefit from staking), put stakes in at planting time to avoid damaging tubers. Tomato cages also work well, and should be put in when planting.
Water: Dahlia tubers need only be watered sparely after planting. Once the lants are growing for best blooming, water once or twice a week during hot, dry weather. In containers daily. 
Fertilizer: Use an organic fertilizer. Don’t overfeed.
Pinching: To encourage the growth of bushier plants with better stems for cutting, pinch out the centre shoot just above the third set of leaves.

Overwintering tubers

You can treat dahlias as annuals, but they can be dug up after the first frosts kill off the stems and leaves and kept through the winter for replanting the following year. Store the tubers in a cool, frost-free place. This is a great way to keep your favourite cultivars going. Dig bulbs or tubers up after frost has blackened foliage. Carefully remove as much soil as you can. Cut the leaves off, leaving a stem about an inch or two long. Leaves and stems are not needed, as the plants are going to be dormant and not making any growth through the winter. You can either carefully wash the soil off the tubers or bulbs, or just let it dry and work it off by hand later. Leave bulbs or tubers exposed to air in a frost-free place for a couple of weeks. Any remaining stem should be dry before going into storage, otherwise rot could develop. Store in old newspapers and cardboard boxes in a cool, frost free place at 5-10°C.