Selection and How to Grow Dahlias

Where does one start?
There are an estimated 60,000 cultivars of which growers can stock only a few.
Questions to answer
Will you be growing them on their own or in a mixed bed?
Will you be bold enough to enter into local flower shows?
Do you just want colour in the garden?
Will you be cutting blooms for the vase?
Criteria
Colour.
Height.
Growth habit, e.g. long, erect stems or compact.
Flower head size, NB: the Giant and Large decoratives can have massively heavy blooms, especially after rain! Not for the faint hearted as it is more difficult to achieve excellent results with these types.
Tips and advice
Water lily types are excellent for both borders and cut flower and many are great in their class on the exhibition show bench.
Large and giant classification types are challenging and very rewarding to grow. A giant decorative, such as Lavender Perfection or Bryn Terfel, will grow to 260 mm - 300 mm across and leads to jaw dropping reactions from visitors!
A bed of dwarf/bedding dahlias will make a stupendous garden display.
For good cut flowers always disbud.
For border display where a mass of colour is the aim, disbudding becomes optional. The blooms will not be as large but will be plentiful.
If you plan to exhibit, select cultivars that have a good reputation on the show bench because they conform to their classification well and consistently produce good blooms. When planning you planting bear in mind that to produce a show vase of 5 blooms one should really grow 16 plants of a single cultivar.