How to divide dahlia tubers
Dahlia dividing; you either hate it (most people), or love it (a select few, including me). We are going to take the fear of messing up out of dividing dahlia tubers. We'll go through the process step by step to help you feel more confident about dividing dahlias and maybe you'll even fall into the love dividing dahlias camp.
To get started, gather all the supplies you need, we use Bridgetown Snips and bypass pruners, which you can buy here, (link) a bowl of bleach water for disinfecting your snips pruners, a good permanent marker, a crate with holes for storage, can also use a basket from the Dollar Tree, dahlia tuber clump, notebook for notes, pen, and stickers for labeling.
To begin, let your snips and pruners disinfect while sitting in bleach water while you take a look at your tuber. The first thing we do is cut off all the dangling, broken necked, & bad tubers, for example ones that may have rot on them. Once we've gotten rid of those, we cut off all the big tails from the ends of the tubers, and also all the small tubers that are smaller than a triple A size battery.
Once your tuber is cleaned up slightly take a look at how all the tubers are connected to the stem. Don't forget to turn your tuber clump upside down as there is often an area where all the tubers are growing from on the bottom and these have eyes as well. What are the eyes and why are they needed? The eyes on a tuber look like a little pimple, for lack of a better word, sometimes they can be hard to see, especially in fall or early winter dividing. It is very important to learn what eyes look like and start identifying them as this is where the stem for a new dahlia will grow from. The tuber itself holds all the energy a new dahlia will need for the initial growth and the eye is where that growth originates. Make sense? It's like potatoes that have the little eyes all over them that will start to grow if left in a warm spot. Dahlias are the same but their eyes are only at one end where they were connected to the stem.
We use our bypass pruners, to cut the stems down to where the tubers are growing and them snip off the tubers, each tuber clump and variety has it's own growth pattern so you will decide how to go about separating the individual tubers. Some people cut the whole clump in half first, I don't usually do that, I have found that the tuber clump is put together like a puzzle and you can begin to snip off the groups of tubers on the main clump sort of in the reverse order that they were formed. Starting from the top, snip a clump of 3-4 tubers that formed off a part of the stem and them divide those down further, making sure each tuber has an eye, and is at least as big as a triple A battery.
Sometimes it is easier to turn the dahlia clump upside down and start from that side. With practice you will notice that each tuber has its own head where it fits together with the other tubers like a puzzle, I like to divide in that way to keep that intact. Sometimes they will even pull apart along those lines.
Once your dahlias are divided, you may have questions about whether some of the tubers are good or not. A viable tuber needs a firm, not squishy body, a neck, a head, and an eye. It takes some practice finding eyes as mentioned before, and sometimes the neck is not very defined on long, slim tubers ou can always keep a tuber and throw it out later, but if you are selling tubers, sell only the ones that you are sure about. I always have a nice little dahlia patch in my compost pile where I throw out all the waste tubers from dahlia dividing, so I guess sometimes you may toss some that would have been good. It's always a learning process that gets easier and easier with practice.
One thing I learned last year is that when tubers are grown from cuttings, the tubers they produce don't always have a defined neck, especially certain varieties. In this instance the tubers are more ball shaped and have eyes where they were attached to the stem, but no visible neck. You can always let your tubers come out of dormancy by warming them up and letting the eyes develop more so you aren't throwing out viable tubers.
After the tubers are divided, we count them record the number in a notebook as well as writing the number on two stickers, one we attach to the outside of the crate we store them in, and the other we place inside the crate. We like to double label everything in case one label fails.
I keep our dahlias at about 85-90% humidity and 47 degrees, I do not add anything to the storage containers with the dahlias because I have found it leads the tubers to rot easier.