Tree Dahlia: The French Alternative

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For dramatic autumn colour, tree dahlias are hard to beat. They are giant plants with huge leaves and stems, and shaggy, lavender flowers resembling ballerinas’ tutus. It’s not only the appearance of the tree dahlia which causes drama in the garden – so do the very brittle stems. One minute you can be proudly showing your tree dahlia off to the neighbours, then before you know it, a sudden gust of wind has blown the whole plant over!

Plant details

Common name: Tree dahlia
Botanical name: Dahlia imperialis
Description: Herbaceous perennial, 3-5m (10-15′) tall. Native to Mexico, Central America and
Colombia, they have thick bamboo-like stems, large bipinnate leaves and clusters of single lavender flowers with yellow centres. Single or double white flowering forms are also available.
Best climate: Tree dahlias will flourish in most areas (including sub-tropical and cold regions) but flowering can be ruined by frosts.

Good points:

fast growing attractive, pendulous blooms easy to grow and propagate stems are tall, straight and thin, so they don’t take up much space

Downside: The stems are brittle and break easily in the wind. Staking may be necessary.
Care: Tree dahlias need a sunny spot, sheltered from wind and frost. They are generally pruned after flowering (in winter), when the spent canes are cut back close to ground level. They can also be pruned in early summer if a smaller and more compact plant is wanted. In December, prune the soft new growth by about one third to a half. Shoots will be 20-30cm (8-12″) and should be shortened to 10cm (4″). Tree dahlias are simple to propagate. In winter select a piece of stem with one, or preferably two, nodes. Plant it horizontally, about 20cm (8″) deep, and stand back.

Getting started:

Tree dahlias are available by mail-order from Digger’s Seeds, PO Box 300, Dromana, VIC, 3936. Phone: (03) 5987 1877. Expect to pay $8 for 8cm (3″) supertubes. More established plants are available from Yamina Rare Plants, 25 Moores Road, Monbulk, VIC, 3793. Phone: (03) 9756 6335. 20cm (8″) pots cost around $15.