You are not alone if you have been at a garden centre and seen the sign that says, “dahlias bulbs,” and wondered about the accuracy of the label. Many people, especially novices, refer to dahlias as being bulbs, but from a botanical perspective, this is incorrect. They are not bulbs. They grow from tubers. The difference, while it may seem trivial, actually can greatly impact how successful you are at growing dahlias.
The best way to clear up the confusion is to examine the characteristics that distinguish bulbs from tubers, and why dahlias belong to one category and not the other.
What Is a True Bulb?
A true bulb is the compact, layered structure of a bulb that you would recognize by the cut surface of a bulb onion, or a tulip that you would have planted. Each bulb is composed of a central growing point surrounded by fleshy scales, which are all then surrounded by a basal plate. The bulb layers contain energy that allow the plant to survive dormant periods, and then grow again when conditions improve.
Daffodils, tulips, and alliums are all spring flowering true bulbs that are favourites to many. The structure of these bulbs makes them happy to remain in the ground for many years.
How Tubers Work and Why Dahlias Are Different
Dahlias, like potatoes, also fall into the tuber category. Tubers contain nutrient dense solid masses and differ in structure as they are swollen roots instead of layered scales.
What is commonly referred to as “dahlias bulbs” are actually a bunch of tubers that are connected at a central stem base referred to as the crown. It is important to note that this crown is the only benevolent point of the tubers.
Even if a tuber is healthy, it will never grow without a piece of the crown attached. This is one of the many why dahlias fail to grow after planting, and it is where the distinction between tuber and bulb starts to make sense.
Why Still Use the Term “Dahlias Bulbs”?
Why is it that the term bulb is still used? Primarily because it is a term the majority of people who garden understand. A bulb for many is a term that applies to anything underground that will eventually flower. This term is often improperly used in seed catalogues, online shops, and casual conversations, and the majority of people simply go along with it.
However, in dahlias case. they are tuberous perennials and treating them as such typically provides better results.
What About Planting and Care?
Dahlias care is a bit different from other flowers because they grow from tubers. Tubers are typically more vulnerable to the cold and wet than bulbs are. Because they are not frost tolerant, dahlias are generally brought in during the fall, and stored in a dry spot that will not freeze during the winters. Soil temperature and frost risk will also impact when you are planting. While many bulbs can be panted well in advance of the growing season, dahlias are best planted after the soil has warmed and the risk of frost has past. Some gardeners like to start dahlias in pots, giving the tubers a chance to wake up before moving the pots outdoors.
Choosing Healthy Dahlia Tubers
When buying dahlias, it can be worth it to look a little closer than the label. A healthy tuber clump should feel firm and not soft and shrivelled. A crown should also be present. While size and condition do matter, a plug tuber can grow into a huge plant and a large tuber can produce nothing.
Some supplies will provide pictures of tuber clusters, and unlike others, with bulb-like shapes, tuber clusters are usually a better example of what the customer is buying.
A Small Difference That Makes Growing Easier
From an everyday standpoint, calling dahlias bulbs will not stop them from growing. Once established, they are generous and resilient plants that give months of colour. However, the slight difference of knowing that you are planting tubers instead of bulbs lends a better understanding of what the plants need. Even though “dahlia bulbs” is a common term in gardening, it is actually a bit more interesting and more nuanced than that. Dahlias have tubers instead, which store energy and wait for the right conditions to grow. When summertime arrives tubers spring to life with their characteristic dahlia blooms. Once a gardener understands this difference, they are on the right path to successfully growing dahlias.