They are plants suited for borders, where they can be arranged in groups for height and colour among other tall plants.
They require a sunny spot and soil that is not too rich in nutrients, rich soils tend to encourage leaf growth at the expense of flowers.
The dahlia like 8cm (3in) flowers appear in July till the first frosts and come in colours ranging from pink through to red, plus white and/or bi-colours.
Bees and butterflies are attracted to the flowers.
Depending upon variety, they can grow from 300mm to 1800mm (1ft-6ft)high
Their long stems make them ideal for cutting,and they last well in water.
Most varieties require some sort of support e.g. stakes, and require deadheading regularly to promote continuous flowering.
Week 14: Sow seeds in pots/trays of seed compost and germinate at a temperature of 18°-21°C (64°-70°F)
Germination normally takes three or four days.
Week 16: Prick out plants into 70mm (3") pots of potting compost and gradually harden them off in a coldframe.
Week 22: Plant them out in well drained moist soil 600mm (24") apart in full sun or dappled shade.