Updated: Apr 12, 2021
It is that time of year again when we start selecting new dahlias to add to our collections. Dahlias can be grown from seeds or tubers planted in the spring/summer and come in a large variety of colours and types. In fact, there are 30 species and over 20,000 cultivars of dahlias.
Dahlias will happily grow in most climates. Dahlias thrive in rich, well-drained soil. The pH level of your soil should be 6.5-7.0, slightly acidic. In colder climates, tubers should be planted only when the last frost has passed. For warmer areas of Australia, around December is a good time to plant your tubers. This will allow your plants to bloom in the cooler months avoiding damage to the flowers from the heat of the summer sun.
When selecting dahlia tubers avoid any that appear wrinkled or rotten. The tubers need to have “eyes” (pink buds). Plant tubers at a depth of 10cm and about 30-90cm apart, using closer spacing for smaller varieties. Ensure the growing tips are facing up. Stake tall growing varieties at planting so as not to damage the tuber.
Seeds are planted out in spring in cooler areas. Tropical and subtropical areas can sow seeds from mid-winter. However, it needs to be noted that seeds do not come true and each seed will produce a different flower. I plant my seeds in seedling pots and then transplant them out into the garden. Seeds grown this way will flower in their first year. Protect young plants from snails and slugs.
Dahlias grow best in moist, well-drained soil with full morning sun, afternoon shade and protection from winds. These plants require at least six hours of sunlight per day.
When plants are approximately 30cm in height, pinch out approximately 10cm of the growing centre branch. This will encourage bushier plants and increase stem count and stem length.
For large flowers you may need to experiment with disbudding. This is a technique where the two smaller buds next to the central bud in the flower cluster are removed. This allows the plant to put all its energy into the remaining flowers resulting in fewer but larger flowers.
This process however is not used on the smaller dwarf varieties.
Plants will naturally stop flowering and start dying back after approximately three months. Once this starts cut back about a third of the plant. Keep cutting back as the plant dies off. Continue cutting back until you have approximately 10cm of stem left.
I get to -7C here and never lift my tubers. However, even though I get a lot of winter rain, I have excellent drainage. So, it is important to know your site. If your soil has poor drainage during the dormant period, you will need to lift and store your tubers.
Every two to three years you will need to divide your dahlia plants.
Did you know?
· Dahlias are named after 18th-century Swedish botanist Anders Dahl. He categorised dahlias as a vegetable because of their edible tubers. The tubers are said to taste like a mix between potatoes and radishes.
· For the Victorians dahlias represented commitment and an everlasting union as a result they have become a favourite flower for brides.
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Images are courtesy of Poppy Pod Contemporary Botanical Artwork