The Dahlia is a beautiful and popular flower in gardens around the world and is one of the most flexible of all flower genuses. Today there are tens of thousands of different types of Dahlias which has been made possible by the fact that the dahlia has eight genes that control its appearance while most other flowers only have two. The high number of different Dahlias also makes it one of the most confusing flowers to buy and plant since it is hard to keep track of the different varieties! Dahlias can be practically any colour, have single or multiple rows of petals - those petals in turn can be round or pointed, and each flower can be as big as a dinner plate or as small as a daisy! The total number of dahlias found in most garden stores are generally much, much lower and typically are chosen to be suitable for your geographical area.
The Dahlia is named in honour of a Swedish botanist Anders Dahl and originates in Mexico. It was brought to Europe during the 18th century by Spanish explorers. The beautiful flowers grew well in European soils, but couldn't survive even the mildest winters, and the dahlia therefore remained a rarity until the invention of the greenhouse and winterization of plants.
Once the invention of greenhouses made the keeping of dahlias easier, botanists starting developing new and beautiful variants of the plants. The earlier mention of those eight genes controlling appearance made it very easy to develop new variants and to cross pollinate those variants to get even more new variants. Today the diversity of dahlias is stunning and it can be hard to even believe that two different dahlias are of the same genus. One of them can be a 4 ft high bush with large filled flowers while the other can be less than a foot high with small simple flowers. At this point in history no one knows how many species of dahlia actually existed in the wild in the first place!
Dahlias are grown from bulbs, or more correctly from rhizomes. The bulbs can be planted in most types of soil as long as the soil is not too wet. It should be appreciated however that the dahlia grows much better in certain soils even if it accepts a wide variety of different soils. You can also buy already grown dahlias in many garden stores - these are usually a little more expensive than the bulbs but can save you a lot of time since you get thriving plants right from the start.
Dahlias require a lot of nutrients and it is strongly recommended to regularly fertilize your dahlias. You should also make sure to give it a lot of water to make sure that it is able to absorb all the nutrients provided to it. If your dahlia grows too big a dahlia typcially accepts pruning well and you can trim it down as you see fit.
Dahlias are a somewhat sensitive plant and should under no circumstances be subjected to sub-zero temperatures, as one single night below freezing is enough to kill a dahlia. If you live in an area where the winter temperature drops below the freezing point and you want to keep your dahlias you'll have to dig up the bulb and keep it in a dark cool place during the winter.