Dahlias flower from the middle of summer to the first frosts in autumn, providing bright colour in the garden for several months. All are frost tender. They can be grown in various soil types, providing that they are fertile and well drained, and are excellent border plants.
If grown for exhibition or for cut flowers, they are best planted in rows in specially prepared beds.
The dwarf bedding dahlias, usually grown annually from seed are suitable for planting in containers. Dahlia flowerheads have a diversity of petal forms in a wide colour range.
Where and when to plant
They may be planted as pot grown plants, dormant tubers or as rooted cuttings from tubers. Plants in leaf may be preferable to tubers, as they are often more vigorous. Dormant tubers however may be planted directly, about six weeks before the last frosts, whereas plants in leaf should not be planted until all danger of frost has passed.
Choose an open, sheltered site that is not overshadowed. Immediately before planting, top-dress with blood, fish and bone at 125g/sq m worked well into the soil. Tie young plants into their stakes to support them as they develop.
Planting pot grown dahlias
Canes should be positioned at the appropriate spacings. Plants that are 120-150cm tall are planted 60-90cm apart. 90-120cm tall should be planted 60cm apart. Water the plants in their pots and leave to drain. Plant with care to avoid disturbing the root ball. Water thoroughly. The plants will make a tuber by late autumn.
The ground is prepared as for pot grown plants. Prepare a planting hole about 22cm across and 15cm deep. Place the tuber in the hole and cover over. Mark the position of the tuber with a labelled split Cane placed just to the side. This will indicate the exact position of the tuber when inserting its support stake. The tuber will take about six weeks to develop a shoot above ground.