In this article, I’m going to tell you everything you need to know to get started with one of the most beautiful flowers in the world, Dahlias Tubers.
History of Dahlias
Dahlias are native to Mesoamerica, specifically Costa Rica, Honduras, and Guatemala. They are particularly well-known in the high plains of Mexico, where they are the national flower. There are 40 different species of dahlias and, believe it or not, 57,000 different cultivars for one specific reason. Dahlias are in the same family as sunflowers, daisies, and zinnias, but they have something incredible that few plants share: they have eight sets of homologous chromosomes.
This is a botanically nerdy way of saying there are many ways that those genetics can be combined to form some of the incredible variants in height, size, flower shape, color, etc., that you see. That’s why there are 57,000 different cultivars because they breed so readily. You would think with that many varieties, tens of thousands, there would be a blue dahlia. But in fact, it is still currently genetically impossible to produce a true blue dahlia.
Dahlia Varieties
In 1846, there was a competition to see if any breeder out there could develop one. And while people have gotten close, there is still no such thing as a true blue dahlia. So if that ever comes out, you better believe I’ll be growing it. When the Spanish first came to Mexico and discovered the dahlia, the native peoples there were using it, not just as a beautiful flower, but also cutting the stems and using those as straws.
And then, of course, the tubers are actually edible, whether they’re gathered from the wild or cultivated for that purpose. Dahlias made their way back to Europe in 1789, when the director of the Botanical Gardens of Mexico sent plant parts to the director of the Botanical Garden in Madrid. They quickly spread throughout Europe to the point where the first new dahlia species in Europe was developed just about 15 years later in 1804.
Because there are so many different types, the Royal Horticultural Society had to classify them into 14 different groups based on the flower shape and the florets: single flowered, anemone flowered, collaret, water lily, decorative, ball, pom-pom, cactus, semi-cactus, miscellaneous, fimbriated, single orchid, double orchid, and peony flowered. What I’m getting at here is if you like a particular flower shape, size, or color, besides blue, dahlias are the plant for you. So let’s figure out how to plant them.
How to Plant Dahlia Tubers in Containers
Growing Dahlia Tubers
Although you can cultivate dahlias from seed, and that’s how all the breeding takes place, if you grow them from tubers or clusters of tubers, you’re going to get a genetic copy of the plant from last season. So it’s a good way to preserve, say, a beautiful sort of orangish-red dahlia. If I use that tuber and plant it somewhere else, I’ll have the exact same plant come out next season.
So let’s take a look at the picture. This is a cluster of tubers. Now, anatomically, you’ve got a tail (the trailing off piece), the meat of the tuber, the neck, and then they all come together to form a crown. That crown is where they all meet right before the main stalk. You’ve got this little chopped-off main stalk that would have shot up, and that’s where all the growth would come out of. The magic piece you really want to be looking for are the eyes coming out right around that crown point. This is where the new growth starts. That is the special sauce when planting a tuber.
If you want to plant by tuber, you can do it two ways. You can plant the entire clump, and there’s absolutely nothing wrong with that. The benefit of that is that you’re guaranteed to get something that comes up. If I just plant one tuber and it doesn’t have an eye, then it won’t come up at all. So if you really want to grow from single tubers, you just need to make sure that you have an eye on every single one. As long as you’ve got an eye, you’re good.
But if you’re in a warm zone, zone eight plus, you can just plant this and then leave it in the ground, ideally forever. It’ll just keep coming up over and over again over the seasons. It just doesn’t get cold enough to freeze the tuber and damage it over the winter. In a cold zone, you’re going to have to dig them up if you want to preserve them. I will say, these probably run about the same cost as your annual ornamental plants. So if you want to not deal with it, go ahead and just leave them in the ground. They’ll die, and you can replant them. No big deal. Of course, you’re just going to have to pay a little more for that.
How I Plant Dahlia Tubers
First, let’s talk about how to plant a dahlia tuber in general. I’m going to use the raised bed as an example because it’s basically just a huge container. So this would apply to container gardening as well. You want to select an area with eight plus hours of sunlight and rich, well-draining soil. They do not want to sit in moisture to the point where I actually am not even watering them after I plant them.
So what I do is grab a single tuber and look for the eye to be pointing upwards. It doesn’t really matter that much, but if we’re being particular, pointing upwards is going to give it an easier shot at life. Go about four to six inches deep. You don’t need to get too fancy or too precise here. Clear that area out and place the tubers facing to the side. Most of these you want to give at least about 18 inches of space. Timing-wise, you need to wait until the soil is 60 Fahrenheit or 15 Celsius or warmer.
Up until that point, you can still grow dahlias, but you can grow them in little containers. You can plant this tuber in a small container, let it size up, even put it under a heat mat, kind of like you do with a tomato before you plant it out, and then go ahead and transplant it out. It really doesn’t want to deal with too cold soil temps.
Caring for the Dahlia Tubers
Watering Dahlias
When tubers start to come up, you want to give them about an inch of water a week. When they’re really growing and blooming, two inches of water. They don’t want a lot of water when you plant them out, but as soon as they start to bloom, you really do want to pick up on that watering, especially if you’re growing pretty large varieties.
Staking Dahlias
Actually, throw a stake in at the same time as you plant because you’re going to have to stake them anyway to keep them nice and upright. So what you could do is take a bamboo stake and put it in at the same time just to make sure you know it’s going to be perfectly oriented. But I wouldn’t stress about that. I just think maybe it avoids hitting a tuber. But again, you can do it afterward as well.
How to Grow in the Ground
Now, it’s not too different when you’re planting in the actual ground, but I’ll tell you a trick that helps a lot. If you’re going to plant dahlias in the ground, which can be very beautiful, you can arrange them around a raised bed, in a pathway, or by a pathway.
Loosen Up the Soil
You want to loosen up that soil. This method will help your dahlias to grow. One way to loosen up the soil is if you have something like a broad fork. You can just come in and do a brief little lift because they don’t want to be dealing with compacted, soggy soil. It’s the surest way to fail with them. They’ll rot out or get diseased. So you can come in and loosen to about 10 inches or so, which this broad fork will do. You can, of course, just use a shovel or a little trowel. Then you come in and bury about four to six inches deep. After you’ve planted your tubers, it’s time to wait for them to grow. And when they get to a certain stage, there are a couple of things you can do.
Watering Dahlia Tubers
As I mentioned earlier When tubers start to come up, you want to give them about an inch of water a week. When they’re really growing and blooming, two inches of water. They don’t want a lot of water when you plant them out, but as soon as they start to bloom, you really do want to pick up on that watering, especially if you’re growing pretty large varieties.
Staking Dahlias
I mentioned staking. Staking will help dahlias to grow upwards and keep them nice and upright.
Pruning Dahlia Tubers
Now, another thing you could do is prune. You could do a bit of a top or a clip, similar to how you might prune basil to bush it out. This would force some bushiness. Let’s say you had a nice pot that was a bit wider and you wanted the plant to be wide as well. Then you would use that pruning method instead of letting it grow upright. That’s sort of just your choice.
Good luck in the garden and keep on growing.