In this post, I’ll explain how I divide dahlia tuber clumps to multiply my collection and get more dahlia plants for next year.
Dividing dahlias can be done in the late fall through early spring. You just want to do it while the plants are dormant.
Why Should You Divide Dahlias?
There are two reasons why I divide dahlias.
First, I want more of my favorites!
Each individual tuber has the potential to grow into a new plant of the same variety. So if I want to have multiple plants of my favorite dahlia variety, dividing a clump into multiple tubers helps me increase the number of plants I have for free.
Some dahlias grow tons of tubers, and others grow less. Typically the dahlias that aren’t as good of tuber producers are the ones that cost the most!
If you don’t have many tubers to divide, you can still create more plants and increase your stock for free. Learn to propagate dahlias using cuttings like I do in this post.
Second, I want to break down my dahlia tuber clumps so that they take up less room to store for winter.
I don’t really room to store a lot of dahlias, and a large clump is oddly shaped and kind of a pain to store. Individual tubers take up less room and you can pack more into a box than a clump of tubers.
It should be noted that if you have the space to store dahlias and you don’t need to increase your stock, you may not need to divide your dahlias at all. It’s totally fine to replant the entire clump the following spring.
Inspect tubers for rot, disease, and damage and remove anything like that before putting them in storage.
A Bit of Dahlia Terminology
Let’s do a quick vocabulary lesson so we can get our terms straight.
Dahlia Tuber: referring to the whole divided tuber, which is the part of the dahlia that you bury to grow a new dahlia plant
Clump: the group of dahlia tubers growing below ground off of a central stem
Tuber: the thick, fleshy bottom part of the dahlia tuber where the plant has stored its energy
Crown: the top part of the dahlia tuber where it connects to the original growing dahlia stem; contains the eyes
Eyes: the part of the crown that sprouts and grows a new dahlia stem
Neck: the section connecting the tuber and crown; dahlias will not grow if the neck is broken
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What You Need to Divide Dahlia Tubers
Before you divide your dahlia tuber clumps, make sure you are in a brightly lit location and have the following tools:
- small, sharp snips like these precision snips
- heavy duty pruners like these FELCOs
- permanent marker
- rubbing alcohol or hydrogen peroxide and a cloth for cleaning
Make sure your pruners are nice and sharp and that your dahlia clumps are clean as they can reasonably be.
1. Start with Clean Dahlia Tuber Clumps and Clean Pruners
The last thing we need is to introduce disease to our healthy dahlia tubers. Wipe off pruners with rubbing alcohol or hydrogen peroxide. You should clean off your pruners after dividing each clump.
Make sure your dahlia clumps are (mostly!) free of dirt and mud and somewhat dry.
Trim the growing stem down very short.
2. Trim Off Little Feeder Roots and Bad Tubers
First, let’s trim off the skinny little roots to clean up the clumps somewhat. This step helps me analyze the clump, remove distracting parts of the clump, and sort of prepare myself for tuber surgery.
If I see any tubers that are rotting or that have broken necks or other problems, I cut those off at this time too.
You can see in the two photos side-by-side above how the clump looked before and after I did a little clean up.
I also check the mother tuber. This is the original tuber that was planted in the spring. If it looks healthy, I leave it alone, but if it’s splitting or just looking terrible, I cut it off.
3. Identify the Eyes
The eyes are at the very base of the stem, next to the neck that connects to the tuber. Each divided dahlia tuber needs to have an eye, an intact neck, and a connected tuber in order to regrow the next year.
Sometimes the eyes appear like little bumps on the stem near the neck of the dahlia.
4. Split the Clump Into Manageable Sections
Once you have identified the eyes, use your heavy duty pruners to cut the clump in half. Cut right into the stem to divide the clump from the top down.
If you have to split the mother tuber, it’s fine to cut through it and sacrifice it.
Continue dividing the clump into smaller, more manageable sections until they are small enough to cut up into individual tubers.
5. Carefully Separate the Tubers
Now you can begin cutting around the eyes to divide the clump into sections or individual tubers, whichever makes sense for the clump you have.
Take your time to separate the tubers. Remember, each divided tuber needs to have at least one eye on the crown, a neck, and the tuber itself.
It’s perfectly fine to leave more than one tuber connected by the eyes.
A tuber as small as a AA battery or your thumb has the potential to grow a new dahlia plant.
I do think the larger tubers store better, though.
If you are having a hard time finding good eyes, just try to cut as large of a portion of the stem around the dahlia neck as you can. This part is the crown.
Try to get at least 1 cm all the way around the neck. Then there’s a good chance that there’s at least one eye on the piece for an eye to form.
In the photo below, I circled the tuber that has a good portion of crown attached to the neck. You can even see what looks like an eye at the top of the crown. The other tuber does NOT have enough crown and likely will not have an eye to sprout.
You should be able to see where the texture changes from the neck to the crown to be able to identify the crown (which contains the eyes).
Cut off as much of the original stem as you can to keep from introducing rot to your saved tubers.
6. Write the Variety Name on Each Tuber
My favorite way of identifying the dahlia tubers is to just write the variety name on every tuber with a permanent marker.
If your dahlia variety has a long name, just shorten it in a way that makes sense to you.
Dahlia Tubers Are Ready For Storage
Congratulations! You should now have a small pile of clean, labeled tubers that are ready to go into storage.
Next spring, you’ll be able to pull your dahlia tubers out and hopefully see little sprouts popping out of the eyes.
Your Turn to Grow
Growing dahlias over these last few years has been a fun adventure. There are so many different kinds and types of dahlias out there.
I wish I could grow them all! I’m curious about what your favorite varieties are.
Which tubers are you splitting and growing out?
Leave your favorite dahlia varities in the comments below.
More on Dahlias and Cut Flower Gardening
Continue on to this post to see how I store my dahlia tubers for winter.
You may also be interested in these other posts on dahlias and cut flower gardening.