Many gardeners around Armidale who grow tree dahlias (Dahlia imperialis, also known as giant dahlias), are anxiously watching the forecasts at this time of year, in the hope that the weather will allow their tree dahlias to flower.
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Tree dahlias flower in late autumn / early winter, which translates to May in our region, which of course means that Jack Frost may well have visited and sent those gorgeous flowers to an early demise before you can get to enjoy them fully!
This year, with later frosts, many gardeners have been celebrating an abundance of fabulous lavender-coloured tree dahlia flowers.
Tree dahlias are herbaceous perennials which are different from common Dahlias as they grow very fast and much taller, to a height of 2 to 6 metres. The stems of the plant are up to 10cm (4in) in diameter and resemble bamboo canes. They provide great colour in late autumn when not a lot else is flowering.
The plants are usually pruned after flowering is finished in winter. The stems will be 2-3 metres or more tall and should be cut close to the ground but above the bulbous part that is the dahlia's tuber. It's a good idea to cover the tuber with a layer of mulch to protect it during winter.
The simplest way to propagate tree dahlias is to use the stems you cut down after flowering finished, cut into 50 cm lengths. The roots and shoots will develop from the nodes, so make sure there are at least two nodes per cutting.
Dig a trench about 10 centimetres deep in a sunny spot protected from frost and wind. Lie the cuttings horizontally along the trench with 2 to 3 in each location to give a good stand of plants.
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As tree dahlias take up a lot of space, place groups of cuttings 80 cm or more apart to give them enough room to grow. Once its roots are well established, a tree dahlia tuber is fairly resistant to frost, though the flowers may still be damaged.
If frost occurs frequently in your garden, replenishing mulch on garden beds will help maintain some warmth in the soil to encourage plant roots to keep developing.
While the soil is still warm is also an ideal time to transplant or plant out evergreen trees and shrubs.
The Armidale Garden Club's next meeting is at 7pm on Thursday 26 May, at the Uniting Church Youth Club Hall, off Rusden St, behind the Uniting Church.
