Plant Profiles: Dahlias

There's been a switch thrown in my garden this week with this season's first dahlia blooms making their appearance. My beloved D. 'Moonfire' has returned right on cue, joined by a surprise reappearance of the pictured D. 'Bonita' above.

Why the surprise? Well, it's in a terracotta pot and had no winter protection, not even my famous Dahlia Duvet. It was so much of a surprise, its stems had been nibbled down to soil level by slugs and snails before I found it. Now it's looking good, and set to be a star of my patio all over again.

D. 'Arabian Night' and D. 'XXX' (as named by Thompson & Morgan when they sent it me to trial) are set fair to join them soon as I can see lots of buds forming. That's the great thing about leaving dahlias in the ground (if you can, and it's always a bit of a gamble, even this far south), the tubers get bigger with each year, and in turn bear ever increasing numbers of blooms.

I'll also be keeping an eye out to see if my Daffy Dahlia returns. This was where one of the bright yellow D. 'XXX' developed a red stripe on some of its petals. It's happened for 2 years now, and after taking the RHS's advice, I now believe it's a chimera.

I've always been a huge fan of dahlias, even when they were out of fashion. I always grow at least one new-to-me variety each year... and for 2016 it's the turn of D. 'Fascination' to take a bow. It's taking pride of place in the terracotta pots on the plinths either side of the central patio steps.

I've only just potted them up, so you'll have to make do with the pictured zingy single bloom for now, until all the buds reveal their promise. I've just realised my garden's taking on a rather striking neon-coloured look this year, as a couple of magenta Geranium psilostemon plants have made giant strides in the double terrace bed. Perhaps they're making up for the dull and damp weather we've been having lately.

What's your favourite dahlia? And do you have a striking new colour theme in your garden this year? I really should issue sunglasses with the above photo!

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Cultivation notes

D. 'Moonfire'

Dahlias are easy to grow and come in a range of sizes from between one foot and five feet high, making them suitable from the front to back of the border, or in pots depending on the variety selected.

They're mainly bought as tubers, though they can be grown from seed, or cuttings can be taken from sprouted tubers.

They thrive in all soil types and aren't that fussy on soil pH. They flower from around now to the first frosts, as long as the spent flowers are deadheaded.

An unknown cactus type

Dahlias hail from South America, particularly Mexico where it's the national flower. They first arrived in Europe as possible alternative crop for the potato - note that some tubers are more edible than others! Today, they're more widely known for their ornamental value after a wider, more successful introduction as such during the late 18th century.

They're a great plant for bees, as long as single flowered varieties are grown. However, I've found plenty of other insect life - such as grasshoppers and harvestmen - sheltering in the double and cactus flowered varieties I've grown. Don't forget that earwigs love them too; I tend to tolerate these, rather than do anything about them, unlike that other pest that loves dahlias... slugs!

If you live south of a line drawn between the rivers Severn and Humber, you can try overwintering them in the ground like I do. Note that tubers don't like the winter wet, so you'll have less success with clay soils, or if your garden's not sheltered.

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Further reading

• The RHS's general guide to growing dahlias - there's much more on cultivation, propagation, pests and diseases etc.
• Wikipedia's dahlia entry - which has lots more on the history and introduction of this plant
• The National Collection of Dahlias is based at Varfell Farm near Penzance, under the stewardship of Winchester Growers. They have a 2 acre garden with 1,600+ varieties on display, and you may have seen their fantastic exhibits at Chelsea Flower Show etc.
• James Wong's guide to edible dahlia tubers, including a recipe for rosti. I've also seen Sarah Raven using the petals as a salad decoration.
• Wikipedia's list of RHS AGM dahlias*, which includes a brief guide to the classification of dahlias into 10 different groups (single, cactus, ball etc.)
• List of RHS AGM dahlia trials with links to each one, which in turn link to trial reports, where applicable
• List of Dahlia species, which currently stands at 42... and over 50,000 varieties. D. coccinea and D. merkii are the two species commonly grown in the UK
• Andy Vernon's award-winning book  The Plant Lover's Guide to Dahlias is fabulous :)

* = for some reason I can't find a definitive list on the RHS website

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Latin without tears

My 'Daffy Dahlia'

Dahlia is named after Anders Dahl, one of Carl Linnaeus's students. Whilst the naming isn't disputed, who did it is; it's often attributed to Linnaeus, who died in 1778, some 11 years before the acknowledged date of introduction. 

According to Wikipedia it's more likely to have been Abbe Antonio Jose Cavanilles, the director of the Royal Gardens in Madrid, who received the first plants from Mexico in 1789, and did much of the scientific work in defining the genus.

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