Dahlia Growing Tips for Hot Climates

The best gardening tips I ever learned came from failure—ideally, failure followed by success. Growing dahlias in Southern California comes with its own set of challenges, but it hasn’t stopped me from truly enjoying these flowers and being fascinated by their behavior in the garden. I hope that sharing my dahlia growing tips will make your experience more enjoyable as well!

My own dahlia growing journey has been filled with breathtaking success and complete failure. The very first dahlia I ever planted in my garden was a ‘café au lait’ and it knocked my socks off! For a beginner, having such immediate success with dahlias gave me a little bit of a false sense of security back then…..’dahlias must be so easy to grow!’ I thought. While I’m thankful that early success encouraged me enough to catapult me into learning all about dahlias, I’m also thankful for the failures I’ve had with my dahlias as well. If you stay tuned, I’ll tell you the story about how I lost all my dahlia tubers one year…..

Dahlias are native to warm climates~ Origins

Did you know that dahlias are native to Mexico and mountainous regions of central America? In fact dahlias are the national flower of Mexico! Dahlias are native to warmer climates and would grow wild on the hillsides in Mexico. Furthermore, the Aztecs cultivated these native dahlias for food, medicine, and for holding water. The Aztec word “cocoxochitl” translates roughly to “water pipe” and was meant to describe the large, hollow stems that dahlias have.

So how did the dahlia gain a reputation for not loving hot climates? Well, the dahlias we grow today are mainly from the dahlias that Europeans took from Mexico and bred for ornamental purposes. Over time, these newer ornamental dahlias were bred for their petals, colors, shapes, etc. over their ability to survive their native climate. Honestly, I often think about these original native dahlias when it’s a hot day and I’m fussing over my dahlia plants!

Keep Soil Cool to Beat The Heat

Maybe this isn’t a concern in other climates, but I found that it’s totally possible to fry your dahlias both above ground and under the soil. Soil temperature is not a dahlia growing tip you see very often, but I learned the hard way. Last year I tried a new dahlia growing bed. It was short (about 8-12 inches tall) and surrounded by stone/boulders. The growing medium I used was also an extremely well-draining potting/raised bed mix. This was a recipe for disaster, as I quite literally fried my dahlias into crisps! There was nothing to save, I lost all my tubers. Granted, the whole point of this new bed was to condense down my dahlia collection because I was planning to grow fewer dahlias in favor of edible plants. Well, the collection got condensed for sure…..

In hotter climates especially , it’s necessary to consider soil temperatures if you want to grow dahlias successfully. So, what will keep the roots cool in the soil? For hot climates, mulching and having deeper garden beds/in-ground beds to start with. I won’t give an ideal bed depth because I think it’s just something to consider and try to make as large as you can. Imagine how hot my stone-built, short, well-draining garden beds would get on a 110 degree day?! I’m melting just thinking about it! Keeping in mind your soil volume (more volume, less dramatic fluctuations) will help keep your dahlias happy.

Also, mulch! This goes the same for all kinds of crops we grow—-mulch does wonders for regulating soil temperature, decreasing evaporation, and protecting root systems. You can find some information on types of organic mulches I use HERE.

Pinching Your Dahlias

Speaking of soil temperatures, I’ve learned that pinching your dahlias produces a result that may actually help your dahlias beat the heat! I should note that I’ve got an entire “beginner’s guide to dahlias” already on the blog, so today’s post is a more in-depth look at what my growing experiences have taught me. Truth be told, pinching is not necessary to dahlia survival in general BUT— the more compact, robust, and shorter plants that pinching can produce seems to really help dahlias band together to survive hotter summer temperatures.

For example, a pinched dahlia plant will create more lateral stems and foliage that is bushy and lower to the ground. My non-pinched dahlias can get a little tall and lanky—sometimes the stems will flop over, thus exposing the fragile stems to the harsh sun. Lower, bushier plants will also help keep the soil covered like a “live mulch” which circles us back to the idea that keeping our soil as cool as possible will help the dahlias survive hotter temperatures.

Supporting your dahlias

Unfortunately, it’s rare that I come upon a dahlia that doesn’t need some support. Personally, there are some I’ve grown that I haven’t supported, but it’s best to be prepared to give your dahlias something to help them stay upright. Luckily, supporting or staking dahlias is quite simple and doesn’t require anything complicated.

I’ve used everything from tomato cages to a bamboo stake with some string to support each plant. This year, as you can see in my Dahlia Growing Tips video (also linked above), I took some large pruned branches and set one at each end of my dahlia bed. From there, I took some garden twine/string and strung it between the two branches to support my dahlias. This has worked just fine. Is it an incredible, permanent installation? No. But It’s practically free and works for the season.

Either way, supporting your dahlias will help you avoid what we talked about before (lanky stems flopping over and exposing your dahlias to sunburn) and make your dahlia bed more organized as well.

Cut Dahlia Stems Deep When Picking

One of the best dahlia growing tips I’ve picked up over the years is the important of cutting long stems in your dahlia patch. Cutting long stems serves a few purposes: first, your cut flowers will last longer than dahlias on puny stems (and be better for bouquets) and second, cutting deep will create more lateral stems and growth for more dahlia buds!

Personally, I tend to use the time I spend cutting dahlias for bouquets to “shape” or prune my plant. I keep an eye out for leaf nodes that are low and possibly sprouting, and try to cut my stems above that node. Unfortunately, cutting your dahlias deep can mean that the occasional bud gets cut as well (it won’t open), but I still find this method of cutting dahlias worth it. Each plant is so generous during the growing season anyway! If you need a little more insight into what I mean by “leaf nodes” and where to cut your dahlias, definitely make sure you check out my YouTube video as well.

Overwintering Dahlias Will Help Them Establish

In mild climates you can overwinter your dahlias in-ground. Did your dahlias get started late this Summer and suffer in the heat? That’s okay! If you let your dahlias overwinter, they will have a much earlier start in Spring and have time to grow larger before the heat arrives. It’s a common struggle for us Southern California gardeners to get our dahlia tubers at a good time in the Spring. Honestly, many providers send them out much later than we need, so it can be tough to get an early start. Overwintering dahlias can really allow the dahlias to start sprouting when they feel ready in the Spring.

If you are able, you can get an early start on your dahlias and by planting them in pots like I did HERE, and keeping them sheltered and safe from frost. Either way, it’s important for us mild climate gardeners to get our dahlias sprouting and growing early so that they can be as large and established as possible before our intense heat.

Fall Planting Dahlias?

There is a school of thought that says dahlias can be planted in mild climates in Fall. I’ve seen gardeners in Texas and Florida talk about this before, and it’s very interesting. Essentially, the idea is that you can plant in Fall for a bloom in the cooler months and then cut back your dahlias (and mulch) to prepare them for an early Spring sprouting. This concept also embraces a “summer dormancy” because it’s just so darn hot for them. If you’ve truly struggled maybe give this a try, but my personal experiences haven’t supported the idea that this would be more ideal for me. Besides, after the first season, overwintering your dahlias in-ground means you don’t need to worry about planting anymore.

For example, both my mom and I leave our dahlias in the ground all year round. If they sprout, I let them. But they really don’t look good or bloom profusely at all from Winter to Early Spring. I get a Fall bloom for sure, but the same effect can be accomplished by simply planting in Spring and just letting the dahlias do their thing. So….I guess I’m saying that, in hot climates, simply just keeping your dahlias in the ground year-round can help you assess the best patterns for their growth. Fall planting can indeed be an option, but dahlias have also worked out just fine for me when planted in early Spring after the dangers of frost.

Choose Specific Dahlia Varieties for your Climate

My last tip for growing dahlias (in hot climates especially) is to keep an eye out for those varieties that simply LOVE your climate. This year, growing eight dahlias side by side, I can really see a difference in the vigor and disease-resistance of certain dahlias. For example, my Danny’s Girl dahlia has gotten powdery mildew twice, is more lanky, and just hasn’t been as vigorous as my Diva dahlia. Oh my! The Diva dahlia has been vigorous, bushy, healthy, and the flowers have had the longest vase life compared to all the others. Whenever you notice these types of characteristics in a dahlia, note it!

Admittedly, I’m intentionally going to keep my dahlia collection minimal. It’s not that I don’t LOOOOVE dahlias, but it’s more because I have a lot of plants I need to grow in my space and have to prioritize. Therefore, I’ll be getting rid of any varieties this year that don’t seem great for inland Orange County and replacing them with new ones next year. Think of this process as curating the “perfect” dahlia collection for your space. As the years go by, your dahlias will naturally be better and less maintenance. Isn’t that amazing?!