SKY’S THE LIMIT FOR DAHLIA
As if the sheer range of colours, flower types and sizes available in garden dahlias isn’t enough, there are other dahlia species to grow. These are tree dahlias and they dwarf ordinary dahlia with stems that soar 3-5m high.
If you thought you saw a dahlia peering at you over a back fence recently, it was probably a tree dahlia.
Tree dahlias (Dahlia imperialis) flower in late autumn and into winter after months of growth. They produce stems of single pink, or occasionally double white, flowers. Like garden dahlias, tree dahlias have brittle stems and are often damaged by strong winds or even a strong breeze.
One of the main reasons for tree dahlias failing to flower is physical damage when a gust of wind breaks off the flowering stem. Early frost can also damage tree dahlias and halt flowering.
I have been eagerly waiting and watching a tree dahlia in my garden wondering if it would ever burst into bloom. Its tall stems have taken it into unprotected territory well above sheltering hedges.
Despite the yellowing growth – due to cold and frost – it has flowered. The flowers are small and white, and it isn’t really the showstopper I’d hoped to see back in autumn but it gets 10 out of 10 for persistence.
To get tree dahlias to flowering stage, grow them in a warm, sunny and very sheltered spot. They are planted in spring using stem cuttings taken from pruned growth.
Water and feed throughout summer and autumn as plants grow to tower over other plants.
Tip pruning the stems in early summer can reduce their height and make them less susceptible to both wind and frost damage.
If you are lucky, admire their late season flowers and then, when they finish blooming, cut back the cane-like stems to ground level. The plants will regrow each summer and the stems can be used to propagate new plants.
Do this by cutting a stem into sections with at least two nodes then laying the pieces horizontally in a container of potting mix. A foam broccoli box is an ideal place to propagate tree dahlia cuttings as it provides enough space for these large, woody pieces, which can measure 40-50cm in length.
Fill the box with damp propagating sand or soil.
Alternatively, lay cuttings in a shallow trench in the garden. Once they begin to grow shoots and roots, move them into a prepared part of the garden. New plants can also be grown from tip cuttings taken in late spring or early summer.
If you have trouble locating these oldfashioned plants, keep an eye out as you are walking in your neighbourhood. Many gardeners put out boxes of cuttings after they prune their plants. Potted plants may also be available in late spring and summer at local fetes or markets where plants are sold.
Sadly, that won’t be at the iconic Claremont Spring Flower Show, which has been cancelled. Organisers were concerned that it would be hard to manage numbers at this very popular gardening event. The good news is plans are underway for the equally popular Cactus and Succulent Show, which is staged in November and the summer show in 2021.