The original dahlias, like dahlia pinnata, come from the warm climates of Central America, but mainly from areas with dryish heat and cooler evening and winter temperatures.
Tropical climates are different. They involve year round heat and intense seasonal rainfall and high levels of humidity.
The technical definition of a tropical climate from the Oxford University Press is:
“A climatic zone typically found in the equatorial or tropical zone and characterized by high temperatures throughout the year (i.e. with no marked ‘winter’ season), generally high humidity, and high precipitation, although the latter may occur in a distinct rainy season.”
So, bearing these differences in condition in mind, can dahlias grow in a tropical climate? Or, perhaps the better question is can dahlias grow in a tropical climate successfully?
What is the evidence for growing dahlias in a tropical climate?
When I started thinking about this question, I was pretty sure that dahlias would not be widely grown in tropical climates. After all, I have been to tropical parts of Northern Australia (Cairns, Broom, Darwin), as well as Singapore and Bangkok and I can’t recall seeing any dahlias, except as imported cut flowers.
Nevertheless, I expected that with some offline research and clever searching around the internet, I would be bound to find some adventurous dahlia growers somewhere tropical.
And I have found some tantalising hints, for example:
- Evidence of dahlias growing in subtropical parts of India, although that is not unexpected, as I have seen dahlias grown widely in sub-tropical parts of Australia;
- An enthusiastic Thai journalist encouraging gardeners in Thailand to grow dahlias; and
- A sumptuous display of actual dahlias growing in Singapore. That got me really interested, until I realised these were exhibiting in the cooled biomes of Singapore’s Gardens by the Bay.
But I haven’t found any direct examples of dahlias growing successfully in truly tropical climates.
That doesn’t mean that they can’t. There just isn’t much evidence to show us that they can.
So, the not-so-short answer to the question about whether dahlias can grow in a tropical climate is: probably not, but maybe.
It is ‘probably not’, because I’m struggling to find any evidence to prove it is possible.
It is a ‘maybe’ because, if you think about it, many of us grow dahlias in conditions that are significantly different from the ideal conditions of Central America. In most cases, the difference is that we have to get the plants through cold winters, with temperatures that are low enough to kill them.
Yet, despite these challenges, we still grow dahlias. I, for example, grow dahlias in Scotland. Summer temperatures rarely get above 24°C (75°F), winter temperatures give us frequent frost, winds can be strong and rain frequent.
But none of that deters me.
What is more, there is lots of evidence that dahlias can grow in very hot sub-tropical climates like Florida or Georgia in the U.S.A and in harsh conditions like outback Australia. In these places temperatures can be very hot, nights are warm, and cooler seasons are not especially cool.
So, if you live in a tropical climate, but you love dahlias and you want to grow them, I suggest you go right ahead and give it a try.
And please, please report back and let me know how you get on. I’d be very keen to amend this article to show some proof of dahlias growing in truly tropical climates.
Benefits of growing dahlias in tropical climates
If you grow dahlias in tropical climates you’ll get all of the benefits that we all get from growing dahlias, including:
- Beautiful and colourful dahlia flowers with a striking visual impact, potentially over two flowering seasons;
- Excellent cut flowers, that can brighten up your home with their vibrant hues and intricate shapes;
- Beneficial insects like bees and butterflies, promoting pollination and a healthy garden ecosystem.
But you’ll also likely get some added benefits:
- A simpler way of overwintering dahlia plants and tubers – basically because there is no winter. When growing dahlias in tropical climates, you will not need to dig up your dahlia tubers annually, as is often necessary in cooler climates. At the end of the growing season, you’ll just need to cut back the foliage and cover it with a layer of mulch to protect the tubers from excessive heat and evaporation;
- The warmer temperatures when growing dahlias in tropical climates will also likely allow for longer growing seasons, giving you more time to enjoy the blooms;
- The increased sunlight can lead to more vibrant colours in the flowers;
- Generally, the natural humidity of a tropical climate is likely to help to keep the soil consistently moist for proper root development and growth.
How to grow dahlias in a tropical climate
In the absence of any clear examples of dahlias growing in a true tropical climate, the best guidance I can give is that you follow the advice in the post where we address the question: “do dahlias grown in Florida?”.
Florida is mostly sub-tropical, with some Southern parts of the state described as tropical, although temperatures can dip to the mid-50s°F (12 to 14 °C) in those parts in January. So, I wouldn’t say it has “no marked ‘winter’ season“, as per the definition a tropical climate above.
If you read the post you’ll see that these are some of the key points to bear in mind:
- Make sure the soil is well drained; grow you dahlias in raised beds for better drainage if need be;
- Plant the tubers deep (8 to 10 inches) as this will help keep the roots and tubers cool;
- Mulch around the plants with an organic mulch which is the best mulch for dahlias;
- Give the plants some afternoon shade;
- Choose the best heat tolerant dahlias you can find.
What problems might arise when growing dahlias in a tropical climate?
If you do try to grow dahlias in a hot and tropical climates some problems are bound to arise. Here are the main issues to look out for and how you might be able to deal with them:
Dahlias prefer like warmth and full sun in temperate climates, but they can suffer from heat stress in hot and humid conditions. This can cause leaves to wilt, flowers to droop, and the plant to become more susceptible to disease.
In tropical climates, therefore, it would be good idea to plant dahlias where they can get a some afternoon shade. If you have no natural shade available, rig up some shade cloth or netting that you can pull across the plants when needed.
Also mist dahlias with cool water in extreme heat.
In tropical climates, dahlias can be more prone to fungal diseases such as powdery mildew and botrytis. This is because high humidity and frequent rain provide ideal conditions for fungal growth.
To deter fungal disease, space plants at least 12 inches (30cm) apart.
Pests vary according to the location you are gardening in, so I can’t give you specific guidance on what to look out for where you are. Here in Scotland, for example, where the climate is very far from tropical, our dahlias are attacked by earwigs, thrips and spider mites.
I used to live in the humid sub-tropical climate of Sydney in Australia, near the bush, and the worst pests there were somewhat bigger: the wallabies that came into the garden and ate virtually everything they could get their mouths around.
The point is that warm and humid environments support many life forms, so you will need think about the pests in your tropical region and take whatever steps you can to deter them.
In areas with heavy rainfall, the soil can become waterlogged, which can cause root rot and other problems.
Dahlias need plenty of moisture to grow well, but they also need the soil to be well-drained, because the roots and tubers can rot otherwise. Therefore, if you have any issues with drainage, dig in some grit and organic matter to try to improve things.
Poor drainage is also a good reason to grow dahlias in raised beds. Given their design, raised beds provide inherently good drainage and ensure dahlia tubers will not be sitting in wet soil. Deep raised beds are preferable for dahlia growing – 10 or 12 inches (25 to 30cm) high.
This is unlikely to be a major problem in most garden settings, but soils in tropical regions can tend to have higher levels of nitrogen than is found in temperate regions.
This can lead to rapid, but weak growth in dahlias, with lots of foliage, floppy stems and fewer flowers.
You should keep in mind, therefore, that it is worth periodically testing your soil and make appropriate amendments to achieve the right balance of nutrients for healthy dahlia growth. In particular, use fertilisers higher in potash/potassium to promote flowering once buds start to appear.
I’ve yet to see evidence that you can grow dahlias successfully In tropical climates, although I would not rule it out completely. I’m sure some resourceful gardeners have made it or could make it happen.
You can certainly grow dahlias in hot sub-tropical climates, especially if you follow the tips in this article and in the post covering how to grow dahlias in Florida.
You can also get much more guidance on growing dahlias in these posts:
- Taking care of dahlias: the trick with deadheading
- Dahlia pinnata: a dahlia original
- How to grow dahlias: the complete guide to dahlia care
- How to overwinter dahlia plants and tubers
- All you need to know about dahlia tubers and dahlia bulbs
- Dahlia varieties: your complete guide to all types of dahlias
- Dahlias in my garden: Six on Saturday
- Dahlia Wizard of Oz – Beautiful pink pompon dahlia
- Can you grow dahlias in raised beds?
- Do dahlias grow in Florida?
- Dahlia Wine Eyed Jill: striking dahlia for border or vase
- Dahlia Ivanetti: magnificent magent dahlia
- Dahlia Night Silence – dusky pink dahlia beauty
- Visit a dahlia farm near you
- Best mulch for dahlias: a comprehensive guide
- Dahlia Islander: large, pink, loud, showy. What’s not to like?
- Heat tolerant dahlias: beat the heat with these 120 choice dahlias
Martin Cole has been an avid gardener for more than 20 years and loves to talk and write about gardening. In 2006 he was a finalist in the BBC Gardener of the Year competition. He is a member of the National dahlia Society.
He previously lived in London and Sydney, Australia, where he took a diploma course in Horticultural studies and is now based in North Berwick in Scotland. He founded GardeningStepbyStep.com in 2012. The website is aimed at everybody who has been bitten by the gardening bug and wants to know more.
Gardening Step by Step has been cited by Thompson and Morgan, the UK’s largest mail order plant retailer, as a website that publishes expert gardening content.
Check out my comprehensive step by step guide, with plain language explanations and ultra-useful images and illustrations. This is for you if you love dahlias and want to the best out of the dahlias you grow.