Dahlia (Dahlia cultivars and hybrids)

Flower Field, Flower Dome

Once again, our striking dinnerplate dahlias makes their comeback on our annual Lunar New Year show! This time, we’re showcasing more cultivars of dahlias with huge blooms over 20cm wide, all lovingly grown by our horticulturists who dedicated great care and effort to nurture them to such impressive sizes.

Native to Mexico and Central America, dahlias can be found growing on the uplands and mountains, from elevations between 1500 meters and 3700 meters, which makes them a temperate beauty! They like it cool and classy, needing temperatures between 15 to 25°C to grow their best, which is why you’ll never find dahlias growing outdoors in tropical Singapore! I’m sure you find them bearing similarities to sunflowers, daisies and the classic chrysanthemums. That's because they all belong to the same family – the aster family (Asteraceae).

Like all these relatives, dahlias also sport the family resemblance in the form of specialized flower heads composed of many tiny florets. Single-flowered dahlias have an outer ring of sterile ray florets, each bearing a petal-like projection from their corolla of fused petals. They are arranged around the outside of the bloom head, and are largely responsible for the bloom’s colour, form, and overall appearance. These ray florets surround an inner centre of lessshowy, tubular disc florets, similar in arrangement to a sunflower or a daisy. In most ornamental dahlia cultivars, however, most or all of the disc florets have been converted to ray florets, resulting in the so-called ‘doubled’ flower form with what seems like a never-ending starburst of ‘petals’.

You might think that ‘dinnerplate’ dahlias are a fancy name for a certain flower class or form, but they are actually an informal term for any dahlia cultivar with an average flower diameter of at least 20cm! (In case you’re wondering, Western-sized dinner plates are about 25 to 30cm in diameter and Asian dinner plates around 20 to 23cm in diameter.) Some of our “classic” cultivars that we grow year after year for their vigorous growth and fantastic flower size are making a repeat appearance, including ‘Kelvin Floodlight’ (not pictured) and ‘Café Au Lait Rose’ (above).

There are 14 groups of dahlia floral forms as described by the Royal Horticultural Society (RHS), the International Cultivar Registration Authority for dahlias. Many dinnerplate dahlias seem to be a part of the Decorative group, whereby they have fully double-petaled flowers with straight, twisted, curled, or wavy ray florets, which sometimes may be curled downward (revolute) or curled upwards (involute), giving them an irregular look. Can you spot the difference in petal curling between in the two dahlia cultivars in the photos above? Dahlia ‘Igen’ has downward curling petals and Dahlia ‘Café au lait Rose’ has upward curling ones.

Featured above in the example of Dahlia ‘Shiranui’ is one of the more uncommon groups of floral forms groups in the dinnerplate dahlia size range: the semi-cactus group. You’ll notice that semi-cactus dahlias produce fully double blooms with ray florets that are usually pointed and rolled backward for more than 25% but less than 50% of their length. The florets are broad at the base and may be either straight or slightly curved inwards.

Other than the dinnerplate dahlias, here are some of the forms of dahlias which I find equally mesmerising for their unique petals. Shown in the photo above is Dahlia ‘My Love’, a stunning cultivar in the Cactus group, characterised by their double-petaled flowers with ray florets that are downward-curling (revolute) for more than one-half of their length, making them narrow, pointed, and sharp-looking, like the spines of a cactus!

Another one of my favourites is Dahlia ‘Lambada’, which is an Anemone group dahlia. This form of dahlia has one or more rows of ray florets surrounding a rounded cluster of elongated, tube-shaped disc florets. In this dahlia group, the disc florets are visible, unlike with the double-flowered dinnerplate dahlias which have had most of their disc florets converted to ray florets. Also, doesn’t the white and yellow colour contrast makes the flowers look like sunny side up eggs?

This year, we are featuring some new dinnerplate cultivars! Come and spot them in Flower Dome and be mesmerised by the variety of dahlias we have on display! For a behind-the-scenes look at how our horticulturists grew these dahlias, check out this feature article!

This article is part of our What's Blooming series.