Sow indoors from January-April at 15-20°C/60-68°F, at a depth of 0.5cm/1/4in. Transplant at the 2-4 leaf stage into 8cm/3in peat pots to avoid root disturbance. Harden off/plant out after last frost, from late May onwards. Space plants 30-75cm/12-30in apart, depending on the variety. Plant in a sunny site, with air between them and neighbouring plants.
Dahlias are heavy feeders, so dig in one or two buckets of organic matter, such as home-made compost or well-rotted manure per sq m/yard before planting. Apply a general purpose fertiliser such as Growmore when planting and mulch to conserve moisture. Liquid feed fortnightly with a tomato feed to boost flowering, or weekly if in containers.
Dahlias need watering in dry weather - aim to soak the roots once a week rather than watering shallowly more often. Seed-sown dahlias have smaller flowers than exhibition varieties but most, apart from dwarf types, will still need staking. Place canes at each corner of the plant and weave string in a web that the plant can grow through.
Deadheading regularly will encourage plants to produce more flowers.
Dahlias grown from seed will have developed tubers by the end of the season that can be kept for next year. Select the best to keep and propagate identical plants by taking cuttings. If dahlias are planted on free-draining, lighter soils, they are likely to survive the winter in milder parts of the country. If the soil is heavy and holds water, lift tubers, otherwise they will rot.
Did You Know?
The thousands of dahlia cultivars available now stem from about 35 wild species, which are native to Mexico and the Central American highlands.
