Dahlias are one of my favorite flowers for cutting gardens large or small. They can be a bit pricey to start with, but they multiply every year and quickly earn back your initial investment. I started with a just a handful in the first year and between dividing tubers and sprouting dahlias, I’m now planting well over 100 plants this year.
If you live in a warmer climate – zone 6 and above – you can treat your dahlias as perennials. This means you could avoid digging them up and replanting every year, which could save a lot of time an energy. Though not the norm, there are even successful flower farms that choose to overwinter dahlias. But alas, our homestead is in a colder climate and we most certainly have to dig up our tubers every year. On the bright side, this means dividing and multiplying our stock every year.
Once you know when to plant your dahlia tubers, you can work backwards and choose the best time to divide. Generally you’ll want to divide in early spring and then plant out after the last frost date. For us in the zone 4b mountains of Colorado, we generally divide in late April, sprout in May, and plant in June. Okay, so let’s get to the details on how to divide dahlia tubers.
Understanding Dahlias and Their Growth Cycle
Before you dive into dividing your dahlia tubers, it’s important to grasp their unique growth cycle and how variety affects the process. Dahlias are perennials that provide vibrant colors to your garden from midsummer through fall.
The Life Cycle of a Dahlia Plant
Dahlias thrive in cool, moist climates and typically begin their growth cycle in the spring. As the ground warms, new shoots emerge from the tubers, which are the plant’s underground storage structures. Through the summer, these shoots develop into sturdy stems that burst into flowers in a rainbow of colors. Once blooms have graced your garden, dahlias continue to flourish until the first frost of fall signals the end of their growing season.
- Spring: Tubers wake and shoots appear.
- Summer: Growth peaks, flowers bloom.
- Fall: Growth slows; blooms fade after first frost.
How to Divide Dahlia Tubers
With your tubers prepared, you can proceed with the division. Follow these steps:
Identify the Eyes: These are found at the base of the last year’s stem. Each section you cut will need at least one “eye” to grow into a new plant.
Slice the Clump: Position your sharp knife at the edge of the clump and cut through the tubers, ensuring each division has at least one eye.
Viable dahlias come in all shapes an sizes. Depending on the variety, you may be able to get 8+ tubers from a clump. Or you may get just one. Whatever you do make sure each tuber has an eye. It’s tempting to save every single tuber piece in the hopes that it will grow, but without an eye you’re just wasting time and space.- Cutting Tips:
- Make clean, single cuts rather than sawing back and forth.
- Avoid cutting too closely to the eyes to prevent damage.
Sprouting Dahlia Tubers
As spring approaches, begin to prepare your dahlia tubers for planting. Check the condition of each tuber and discard any that show signs of disease or rot. Before planting, allow the tubers to gradually acclimate to the warmer temperatures by bringing them into a slightly warmer area if they’ve been in a particularly cool storage.
We have a very short season and prefer to sprout our dahlia tubers before planting. This allows us to take cuttings and also means we’ll get blooms a bit earlier in the season, which is great since we sell at the farmer’s market.
After dividing the tubers we simply place each one in a container and fill with dirt up to the neck. You’ll want to keep the eye above the soil level.
Planting Dahlias Outdoors
Plant dahlia tubers when the soil has warmed and there’s no longer a risk of frost. The soil temperature should ideally be above 60°F (15°C).
Dig a trench about 6-inches deep on their side. Aim for about 12-inches between tubers. As you can see in the video below, you can plant sprouted tubers this way or un-sprouted.
By following these detailed care steps, you’ll set your divided dahlias up for a robust and beautiful display in your garden.
