From these two species came the breeding and improvement of dahlias.

Progress was slow until Dahlia juarezia, the Mexican cactus dahlia, was introduced.

Garden display blooms include varieties of large and small ball types, orchid, stellar, formal decorating, cactus, giant medium and small miniature.

Some varieties are available at local nurseries and retail garden centres.

Cactus dahlias with medium-sized quilled petals make attractive cut flowers for inside display. Some of the nicest varieties are cha cha, Edith Humphries, hillcrest, Jules Simon, mariner and Mrs Rees.

Dahlias thrive best in a warm, sunny position being careful to shelter from strong winds which can damage the hollow, brittle stems so when planting tubers, secure them to a stake approximately 150cms in height.

Plant in fibrous soil rich in plant food. Dahlias do best when they are planted alone in beds that are raised well above ground level; timber edging can be used to achieve this.

After flowering, they should be left to dry off naturally in order to mature the tubers. Do not lift too early and it is best to wait until the tops are cut back from early frosts.

If possible, store in a bush house or alongside a fence, giving careful attention to removing snails who will eat the new shoots.

Dahlias can be grown by seed resulting in the plant producing flowers in about six to seven months in spring. When seedlings are large enough to handle, plant out in nursery rows until they flower.

Not often seen today is the species Dahlia imperialis, the tree dahlia which is unusual in its habit and culture. It grows to a height of 3 metres with a beautiful mauve flower which droops from the tip of the stem.

Propagation is achieved by laying the stem in a furrow in the ground and covering with soil.