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Overview
Dahlias are tuberous perennials that produce a spectacular display of flowers through summer and into autumn.
They have attractive, mid green, lobed foliage, hollow stems and the flowerheads are beautifully colourful, though the number of shapes and sizes vary considerably.
Single flowered Dahlias have blooms with a single outer ring of florets, which may overlap, the centre forming a disc.
The simple, yet beautiful blooms are held aloft on stiff, upright stalks and make excellent border plants and cut flowers.
Dahlias in general have returned to popularity in recent years and the simple elegance of the single flowered group has enjoyed particular success. This is most likely due to its ease of growing, compact size and ability to fit in amongst other plants either in the border or the vase.
As they have grown in popularity so too new varieties have been bred. From Holland comes the 'Happy Single' series with its distinctive dark foliage and from New Zealand the 'Mystic' series amongst many others.
They all make excellent border flowers providing amazing colour and are one of the very best cut flowers.
Soil: Any average, well drained, friable soil will do. Some added organic matter like compost or animal manures will help, but not too much. Ridging up the soil will assist drainage and help warm it too.
Choose a sunny location, around 6 hours per day is ideal, with shade from the scorching afternoon sun.
Plant after the colder nights have passed (end October in SE Australia - just before the Melbourne Cup). September is OK in Queensland.
Moisten the soil before planting but not directly afterwards - moist is good, overly wet is not.
Lay the tuber on its side and cover with soil around 10-15cms deep. They will need around 80-100 days to bloom.
Maintenance: Water sparingly after planting then increase to 2-3 times per week once the first sprouts come through. Do not let them dry out.
Liquid fertilise with a low nitrogen formulation one month after planting and again a month later.
Pinching out smaller buds helps produce bigger blooms.
Keep well watered as the buds set and from then on until they die back in autumn when you can trim back the dead foliage until next year.
Note: Fertilisers produce foliage and water produces blooms.
Hand weed, do not use herbicides.
When cutting flowers include plenty of stem, in fact the length of your forearm is best even if that includes side buds, this helps stimulate more flower production.
In warmer climates they can be left in the ground over winter but Dahlias generally go better when lifted and kept in a cool, dry location over the cold months. This also gives you the opportunity to remove any weakling tubers.
Keep your tubers from drying out - storing in peat moss helps and try to maintain temperature around 7-8c.
Diseases: Two spotted mite, aphids, slugs and snails.
Powdery mildew can be a bother so try not to water the foliage, better to deep soak the roots only.
Other Species: There are around 35 original species in the Dahlia genus but thousands of named cultivars have been segregated into fourteen main groups to help identification.
These include:
#1. Single flowered #2. Anemone flowered #3. Collerette #4. Waterlily #5. Decorative #6. Ball #7.Pompon #8. Cactus #9 Semi-Cactus #10. Miscellaneous #11. Fimbriated #12. Star #13. Double Orchid #14. Paeony
Practically all modern cultivars have Dahlia pinnata and Dahlia coccinea as original parents though Dahlia hortensis is also present in the overall mix.
Comments: The Dahlia is the national flower of Mexico and was named after Dr Andrew Dahl a Swedish botanist .
The Dahlia was first brought to Europe from Mexico where it was grown initially at the Madrid Botanical Gardens. From there it spread across Europe and the British and Dutch have been largely responsible for the breeding of thousands of cultivars.
Author: Bob Saunders.