Dahlias are one of the most rewarding summer-flowering bulbs that gardeners can grow. With their riotous colors and ability to bloom from midsummer until frost, it’s no wonder they are so popular. One of the great things about dahlias is that you can increase your stock from year to year by separating the tubers when they go dormant. But when is the best time to divide dahlia tubers? In this comprehensive guide, I’ll share tips on separating dahlia tubers in spring for a successful division.
Why Spring is the Best Time to Divide Dahlias
The ideal time to split up dahlia tubers is in early spring, before you plant them out in the garden. Here are some key advantages to dividing dahlias in spring:
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The eyes are more visible – In the spring, you can easily spot the eyes (the places where the new shoots emerge) on the tubers. This makes it simpler to divide them properly so that each section has an eye.
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Prevents overcrowding – Dividing crowded clumps in spring prevents tuber overcrowding leading to healthier, more vigorous plants.
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No rush to replant – When you divide in spring, there’s no rush to get the tubers back in the ground. You can take your time splitting them up.
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Tubers are firm – Spring tubers are firm and pliable compared to freshly dug tubers, making division easier
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Allows inspection – Dividing in spring enables you to inspect for any rot or other issues on the tubers before replanting
Step-by-Step Guide to Separating Dahlia Tubers
Follow these simple springtime steps for dividing your dahlia tubers:
1. Remove the Tubers from Storage
Gently remove your stored dahlia tubers from wherever they were kept over the winter – this might be a cool basement, unheated garage, or buried in mulch outdoors. Check for any signs of rotting or mold. Discard any tubers that are soft or show dark colors.
2. Allow Tubers to Warm Up
Bring the dahlia tubers indoors and allow them to warm up for a few days before dividing them. This helps prevent snapping or cracking the tubers during division. Aim for temps around 65-70°F if possible.
3. Wash and Dry the Tubers
Wash any remaining dirt off the tubers by dunking them in a bucket of water and gently scrubbing with your fingers or an old toothbrush. Dry them thoroughly before dividing.
4. Prepare Your Workspace
Get your workspace ready before dividing the tubers. Make sure you have:
- Sharp, sterile garden knife or pruners
- Container of water to moisten tubers
- Trays or containers for the divided sections
- Labels and pen for marking varieties
5. Examine Tubers for Eyes
Check the crown (the top part) of each tuber for the eye – this will look like a small node, bump, or emerging sprout. Having an eye means that section can grow. Avoid any pieces without an eye.
6. Divide the Clump
If a tuber clump is very large, you may need to cut it in half before separating further. Use your clean, sharp knife/pruners to slice through the tuber clump.
7. Cut or Twist Apart
Make divisions by slicing tubers apart with your tool. Or gently twist and pull sections to separate. The goal is tuber pieces approximately 2 inches or larger.
8. Moisten and Mark Divisions
Moisten each divided tuber section by dipping in water. Let dry briefly before marking with the variety name using labels or a permanent marker.
9. Allow Divisions to Dry
After dividing, lay the tuber pieces out and allow to dry for 2-3 days before planting. Discard any that show mold or rotting.
10. Plant When Soil is Warm
Once the divided tubers have dried, you can plant them out in the garden. Wait until all danger of frost has passed and the soil has warmed up, usually around May.
What to Avoid When Dividing Dahlias in Spring
To safely divide dahlias in the spring, avoid these common mistakes:
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Dividing without a visible eye – An eye is crucial for growth, so only divide sections with an eye present.
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Letting tubers get too warm – Don’t allow tubers to overheat before dividing or eyes can dry up. Ideal temps are 65-70°F.
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Making divisions too small – Divisions should be at least 2 inches; smaller sections might not grow well.
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Not disinfecting tools – Always sanitize and sharpen tools before dividing to prevent any disease spread.
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Failing to label – Proper labeling ensures you don’t lose track of dahlia varieties when dividing.
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Replanting too soon – Wait until divided tubers have dried for 2-3 days before planting to prevent rotting.
Caring for Dahlias After Division
Once you’ve mastered dividing dahlia tubers in spring, be sure to provide good care after planting:
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Water well – Ensure regular watering as tubers establish roots. Dahlias need about 1 inch of water per week.
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Use fertilizer – Feed with a balanced fertilizer when growth starts and every 4-6 weeks after.
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Stake tall types – Stake floppy, tall dahlia varieties to prevent damage from wind/rain.
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Pinch out tips – Pinching out early shoot tips encourages bushy growth.
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Deadhead spent blooms – Deadheading keeps plants looking tidy and encourages more blooms.
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Watch for pests – Check for common dahlia pests like earwigs, slugs, and aphids.
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Dig up tubers in fall – After the first frost kills foliage, dig up the new tuber clumps to store again.
Key Takeaways on Dividing Dahlias in Spring
- Spring is the optimal time to divide dahlia tubers – the eyes are visible and tubers are firm.
- Allow stored tubers to warm up for a few days before dividing.
- Use clean, sharp tools to divide tuber clumps into sections with at least one eye.
- Moisten and label divisions before allowing to dry for 2-3 days.
- Wait to plant until after the last frost when soil has warmed up.
- Provide good care like watering, fertilizing, and staking for success after planting.
Size doesn’t Matter (mostly)
One common concern people have when they receive a dahlia tuber is, ‘This is so small. Will this produce a quality dahlia plant?”.
When it comes to tubers, size doesn’t matter – to a point. First, let’s talk about what a dahlia tuber is. A dahlia tuber is the large root of a dahlia plant. There is a starchy body inside a dahlia plant that gives it food, water, and nutrition to grow until it gets roots that can feed it.
As long a dahlia tuber is large enough to accomplish what I described above, it is big enough. How big is that? When I train new workers, I tell them that a tuber should be at least my little finger’s length, which is about the size of an AAA battery. Tubers smaller than that will produce a plant but it might not produce as many flowers. It should create quality tubers that can be divided for the following year. No matter what kind of tubers I’m sending, I try to make sure that the smallest ones are about the size of an AA battery. Always remember that a tuber that is longer than it is thin is still fine. The battery measure is more about total volume of the tuber than the thickness or length.
Representative examples of the variety of shapes and sizes dahlia tubers come in. AA battery for size reference. 1. Peaches n’ Cream 2. Blyton Softer Gleam 3. Bonanza 4. Cafe au Lait 5. Hamari Gold.
In the photo above, you can see the variety of shapes and forms different tuber come in. These are all examples of quality tubers I wouldn’t question planting in my garden or on my farm. If I had to pick a perfect size tuber, I would want it to be around the size of the two Bonanza examples (#3 in the above photo). It’s important to note that not all varieties will grow tubers that shape or size, and they don’t have to be that size or shape to make a good plant.
I also want to add that there is such a thing as “too big”. It might not be possible for a dahlia tuber to produce more good tubers or grow a large root system if it is too big. You can think of it like the dahlia not having to go find more food and water because it already has a lot of it. There may have been new tubers on the top of the plant, but when you dig these up in the fall, you only find one mother tuber. How big is too big? Usually, I don’t like them when they’re bigger than a regular coffee mug.
Remember that if the plant normally makes a lot of big tubers, like Ferncliff Copper, it’s fine if the tubers you plant are bigger. Should you think that a tuber is too big, you can cut off a piece of the back half to help the roots grow more.
Another common question I see on various flower forums is, “My tubers dried out in storage. Will these make it?”.
Dahlias are survivors. What I thought was a pile of trash turns out to be full of dahlias every year in late June when I go out to the compost pile. While they have a will to live, there are still basic things to look out for. As they say, a picture is worth a thousand words, so I dug through my tuber storage to find some to show you.
In the photo below, you will see a tubers ranging from perfect with no desiccation (#1) to completely dried out with no hope (#7 – #9). In my field, I will plant anything that looks like #1 – #4 without any hesitation. Each of those will produce a quality plant. With #5 and #6, it is a little more debatable. #5 has an eye actively growing but as you will see in the next photos, that does not guarantee it is viable.
Various states of desiccated dahlia tubers
In the two photos below, you see the same tubers. The first picture shows the outside of the tubers, and the second picture shows the inside of the same tubers after they have been cut in half. When you handle a tuber, you can feel if there is any moisture left in it. Although #1 looks really shirred, it was still malleable and you could feel there was moisture inside of it. The same was true for #3, even though it looks arguably worse than #2. Although #2 had a viable eye on it, the tuber than held all the plants energy was completely dried out and would not have been able to support that eye. There was no hope for #4 and looking inside of it confirmed this. In the examples below, I would have planted #1 and #3 in my field but not #2 or #4.
In short, just because dahlias look dry doesn’t mean they won’t grow. If you feel the tuber, you can tell if it still has water inside. They will be fine as long as they are not completely dry.
Examples of dried tubers. Look at the next photo too see what they look like inside.
Examples #1 and #3 both still have white flesh inside, while #2 and #4 are completely dehydrated and brown. The black under the tuber are rocks I used to prop them up for the photo.
This is for the most part common sense, but I will talk about tuber rot for a moment. If you have a rotten tuber, it won’t grow.
What causes tuber rot? It can be fungal or bacterial. It usually gets in through a cut made when you lift or split the plant, too much water on the tuber, or rot that moves down the plant’s stem and into the tuber clump. It will first look brown or black and then travel deeper into the tuber.
If you see rot on your tuber, cut it out until you only see clean, white flesh inside. There won’t be any life in the tuber if there is rot all the way to the neck. If you find rot all the way through the crown that is attached to that tuber, it won’t work. If you can get rid of all the rot, the tuber should be fine. Sometimes it needs a little dahlia surgery.
Below is an example of a dahlia tuber that is not viable due to rot. It looked fine from the outside, but when I picked it up, I felt a soft spot and knew right away that it wouldn’t work because the tuber’s neck was rotten.
It is common to see a little mold growing on the cut ends of a dahlia tuber. It’s fine to have a little mold on the dahlia tuber as long as it stays on the outside and doesn’t get inside and cause rot. You can normally squeeze the end of the tuber and tell if the rot has traveled into it.
An example of some mold growing on the cut end of a dahlia. If there is only a little mold on the tuber, like in this picture, it usually doesn’t hurt its ability to grow.
Dahlia Tuber and Splitting Guide
I thought now would be a good time to start a blog, which is something I’ve wanted to do for a while. Spring is coming soon and it’s getting warmer. I’d like this to be a casual conversation where we can mostly talk about growing tips or other things going on at the farm. What a better way to to kick it off than with a review on dahlia tubers?!.
Over the last five years we have split over 200,000 dahlias on our farm. For us, it’s just muscle memory at this point, but for some it can be really hard. The most common questions I get are about how to split and store dahlia tubers. This is also what most people have trouble with when it comes to these lovely flowers. In this post I am going to concentrate on the tubers themselves rather than on their storage. Our Dahlia Care page has good information on how to store tubers.
Just like people, different dahlia varieties have unique characteristics and come in many different shapes and sizes. Some might have long and skinny tubers, where others are short and fat. Some plants may make a lot of tubers in a clump, while others may only be useful for propagating from cuttings because they don’t make many or any viable tubers. Some store well, while others are notoriously difficult to store without them rotting or dehydrating. In short, when working with mother nature, you cannot look at tubers as an ‘off the shelf’ widget. Since dahlia tubers come in many different types, there is no one “standard” shape or form. Each one will be different.
Here are some examples of different dahlia clumps that I pulled out of storage before they were split. This is what they look like when we put them into storage. There is still soil on them and they are not cleaned up too much yet.
A typical clump of Rip City dahlia tubers. It is one of the most productive varieties we grow.
A little better than average clump of Sweet Nathalie dahlia tubers.
A clump of Sea Nugget dahlia tubers. You can easily split this group of tubers five or six times, even though they are on the small side.
Dividing Dahlias! ✂️ // Garden Answer
FAQ
Can I split dahlia tubers in spring?
What happens if you don’t divide dahlia tubers?
What is the best tool for dividing dahlia tubers?
When should you divide dahlia tubers?
If you are learning how to divide dahlia tubers, the first decision you need to make is when to divide dahlia tubers. Some gardeners divide their dahlias in the fall before storing the tubers away for the winter. Some people divide dahlias in the spring. There are advantages and disadvantages to both. Can you divide dahlia tubers in the spring?
How do you divide a dahlia plant?
Dahlias are perennial plants that develop tubers underground. These tubers store nutrients and energy that allow the plants to survive the winter and sprout again in the spring. Dividing dahlia tubers involves separating these storage structures into smaller sections, each of which can grow into a new dahlia plant.
How to propagate dahlia plants?
One of the best ways to propagate dahlia plants is by dividing their tubers. Dividing dahlia tubers not only allows you to create more plants from a single parent plant, but it also helps in maintaining the health and vigor of the existing plants.
Do dahlia tubers dry out?
In our damp climate, dahlia tubers take a long time to dry out, so when separating dahlia tubers in spring, they have had a chance to dry out for months in our garage. Sometimes dividing dahlia tubers in the spring takes more muscle power. If the dahlias are in a large clump, dividing can be tricky.