With most plants, it’s easy to distinguish if they are perennials or annuals. They either come back every year or grow one season and then die. But dahlias are a little confusing, for a good reason. So let’s dive into this a little more and talk about whether dahlia plants are perennials or annuals.
A Bit Of Background On Dahlia Plants
Dahlias are part of the Asteraceae plant family and are closely related to common flowering ornamentals like daisies, sunflowers, zinnias, and mums. Unlike other flowers that primarily reproduce from seeds (e.g., sunflowers), dahlias grow from small tubers, not bulbs, that grow underground. These tubers are similar to potatoes with a thin protective skin and buds or “eyes.”
The fact they reproduce from tubers is key to understanding dahlias’ life cycle.
Understanding the Difference Between Annual and Perennial Life Cycles
One of the primary purposes of all plants during their life is reproduction. They want to grow and thrive in an attempt to reproduce and pass along their genetic information to offspring. How long this takes varies in different plants. Some plants reproduce quickly (annuals), and others reproduce over a long life span (perennials).
What Are Annual Plants?
Annuals cycle through their entire life in a single growing season. They go from seed to flower and seed again within a few months, and all of their plant parts die annually. The dormant seed produced in the fall is the only thing that bridges the gap between one generation and the next.
These plants adapted to demonstrate this quick life cycle because of unstable habitats. Because they never knew what conditions would be like, their primary goal became developing seeds to pass on genetics as quickly as possible. When they have enough water and suitable temperatures, seeds germinate, taking advantage of what could be a narrow window of opportunity.
What Are Perennial Plants?
Perennials, on the other hand, persist for numerous growing seasons. In most climates, the vegetative part of the plant dies back to the ground every winter and then regrows from the root system come spring. These plants may bloom and produce seeds every year they are alive if the conditions are suitable.
Unlike annuals that have adapted to uncertain growing conditions, perennials evolved from very stable environments. The problem with stable habitats, though, is they often support many plants. These plants compete with one another for space and resources. Due to this, perennials want to live as long as possible, producing seeds over many years.
The Official Dahlia Classification
Dahlias are officially classified as “tender perennials”— A classification that is code for “it’s complicated” in gardening terms. In basic terms, this classification means their lifecycle depends on the hardiness zone. They may grow as annuals or perennials based on an area’s winter conditions and if they can survive until spring.
Technically, a tender perennial is classified as a perennial that can live for many years but isn’t winter hardy. They are often called annuals for simplicity’s sake. However, they aren’t true annuals because they can survive for more than one growing season.
Confused? Maybe this will help.
How To Successfully Grow Dahlias Based On Your Growing Zone
- Zone 10 and Higher: Dahlias grow as perennials and don’t need winter protection.
- Zones 8 and 9: Dahlias grow as perennials but need winter protection. The foliage dies back after a hard killing autumn frost. You then need to cover the planting bed with straw, mulch, or bark chips to insulate it over the winter.
- Zones 7 and Lower: Dahlias grow as annuals if left in the ground—winter temperatures and snow kill the tubers or make them rot. They grow as perennials if you dig up the tubers and store them between 40 and 50°F for the winter, planting them again the following spring.
Unsure Of Your USDA Plant Hardiness Zone?
The United States is broken up into USDA plant hardiness zones based upon annual minimum winter temperatures. Sections across the US are separated into 10°F zones and aid in determining the harshness of your local winter conditions.
Solving The Mystery of A Dahlia’s Life Cycle
Coming back around to the question, “are dahlias perennials or annual plants?” the answer is yes, they are both. But they aren’t in some places. In warm climates, dahlias grow as perennials. You can grow dahlias as annuals or perennials in cooler temperatures, but they need to be protected from the cold or dug out of the ground.