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Dahlia Dividing Observations
by Suraya David-Sadira, FTT and Assistant Mini-Farm Manager, TJC

In 2021, we established an experimental 10-Bed Unit (10BU) at TJC complementing the ongoing research on this topic at VGFP and other 10-BU locations globally. The diet design for this experimental bed included dahlias as a versatile carbon/calorie/income crop. You can find a good intro to edible dahlias here.

Dahlias growing in the TJC 10-bed unit 2021Yesterday in the garden I mostly divided Dahlia tubers. They are such incredible and beautiful plants and the dividing process is so particular that it brought me some sense of anxiety to just start hacking them up. Each year when you plant a dahlia tuber it will multiply, producing a ball of many often interwoven tubers. In some locations where it only lightly freezes, dahlias can be left in the ground over winter. However in places that experience a hard freeze it is best to take the tubers out of the ground.

Once you take the tubers out of the ground you then can decide whether you want to divide them or not. If you decide to leave them undivided, then you will likely have strong healthy plants with even larger tuber balls next year. However, if you do decide to divide the tubers, you can multiply the amount of plants you have, and harvest some tubers for eating; but you do run the risk of butchering all your tubers. The dividing process is very delicate and complex so it is important to have good tools and be vigilant in your method.

Dahlia roots consist of the main body of the tuber, then often have a very skinny neck, and then connect to the main stem. Where the neck connects to the main stem there is a little eye that looks similar to a potato eye. In order for each tuber to grow a new plant, it must have all its parts intact: the main body, the neck, and the eye. It is easiest spot the eye if you divide the tubers the same day they are dug from the ground. The longer the tubers are out of the ground the harder it becomes to spot the eyes. NOT ALL TUBERS YOU DIVIDE WILL END UP HAVING EYES. It is totally natural that some dahlia tubers will break off at the neck or not have an eye. Only about 50% of your tuber will produce viable plants in the spring. Whatever breaks or you don’t need, you can set aside to eat.

You could also choose to wait until the spring to divide the tubers once they have already sprouted, but this method also comes with its benefits and challenges. It will likely be easier to see the tuber eyes once they have sprouted, however, it may be more challenging to actually split the tubers. By waiting to split the tubers I suspect you will also get fewer splits and could alter the amount you harvest for food.

Steps to divide Tubers

If you are planing to dig up dahlia tubers do it on the week of the first frost. Make sure your Dahlias are labeled before they stop producing flowers.

  1. Dig up bulbs by inserting a garden fork one foot from where you think the center of the dahlia tuber ball is. The tuber balls multiply over the growing season and are planted about a foot deep, so the tuber balls can be a food in diameter and grow deep into the ground so start prying them up from afar to avoid puncturing them. Since they grow deep in the ground you may want to dig a little trench around the ball so that you can pry from deeper with your fork. Start wide and work your way in until the tuber ball emerges.
  2. Place tubers aside with their labels.
  3. It is easiest to divide tubers within an hour of pulling them out of the ground so it may be good to work through the bed in sections. A longer you wait the harder it becomes to see the eye of the dahlia.
  4. After you have a few tuber balls out of the ground, use a hose to wash away all the dirt you so you can see all the parts of the tuber.
  5. Dahlia tuber balls can be intricate and tangled, so it is important to be careful and have good tools. Each tuber needs to have a tuber body, a neck, and an eye to be viable. Carefully separate the tubers using garden clippers. Some of the tubers will break off at the neck, and some tubers wont have a viable eye. It is a complicated task you kind of just have to learn by doing.
  6. Lastly ,weigh all the tubers and record all the data. Store the tubers with a viable eye and enjoy eating the rest.


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