Dividing Dahlias

Dividing dahlias may seem intimidating, but with a few simple tricks, they are easy to separate for storage and future plants. The first time we pulled tubers, we were surprised to find one tuber in some cases had become 20 or more. We were equally overwhelmed when we unpacked them in the spring.

Its ok. This isn’t as scary as it seems. Breaking down the dividing process into steps, you can cut your tuber clumps easily to divide the plants.

If you are wondering how to begin with getting them out of the ground, start here.

Once the tubers are lifted, many gardeners start with washing. If you are in a climate where the plants come up in dry dirt and you can brush the dirt off, then a wash isn’t required. You can use an old paint brush to gently work the bulk of dirt off the tubers. If you live in an wet area like us, the tubers are going to have mud that will not easily brush off. In this case, start by washing thoroughly. Its important for all soil, organic material and any little rocks to be removed by the necks and stalk of the plant. It’s ok to have a bit of dirt remaining, or dust, but too much dirt will obscure what we are looking for and dull your tools. You need to see where the tubers attach. A good wash probably reveals a tangled mass.

The next step is to cut off all the feeder roots and any stick small tubers. Tubers will lose a bit of moisture over the year. A good rule of thumb is if they are less than a pencil diameter in width, they will likely dehydrate, are prone to breaking, and not worth the storage space. Trimming feeder roots and tiny tubers will help you see more clearly the good tubers. The images before show the tuber mass before and after. It greatly reduces the chaos of the tuber mass by simply clipping the feeder tubers off.

Occasionally a tuber will grow it’s own feeder tuber. It can look like the photo above and on the right, or sometimes you will see 2 or more fat feeders off the tail of the tuber. No matter how pretty these tubers are, they are not connected to the crown and will never have an eye. They are a blind tuber. You can compost them, or eat them like a potato. There are many recipes for dahlia baked goods.

With all the additional material removed, you should now have a clear view of stem and where the tubers attach to the stem. Our goal is to find the eyes before dividing the dahlias. Eyes are the tissue of the plant that will grow stalks next year. Sometimes you will find one eye, but often there will be several associated with each tuber crown. Yet some tubers will not have a crown or an eye. This is why they are called blind tubers.

If you dig your plants within a week of frost or a cut back with the intent of dividing, you will likely have eyes like this. If you wait longer, the eyes will become sprouts which are white until they break the surface and only then make chlorophyll. If you have green sprouts under the surface, this can be an indicator of disease. If you dig after the plant has gone dormant and it is too cool to grow, you may not see eyes until the following year. This makes a fall divide more challenging and you will have to look for swelling of the crown as an indicator of a viable tuber.

Tubers with nice swollen crowns and the white dots of emerging eyes for the next year.

Your turn. Can you find several white eyes which will become next years plants.

The goal from here on out with dividing dahlias is to gently work apart the stalks and use sharp nippers, or a dahlia knife to carefully cut a crown and tuber off the main stalk. Find the one that is easiest to get to. As you start to remove more and more tubers, it gets easier and easier to divide. The images below are a series of divides until the whole plant has been dismantled into tubers for next year.

This clump would not separate by the stalks so I began by cutting into a stalk that had two tubers attached. Just above the two arrows on the right you can see where a diagonal cut was made with disinfected pruning shears. Once this clump of two was removed, it was easy to nip them into their own. You can see two tubers on the left with arrows pointing to their swollen crowns. They were next.

Timber! Or at least it looks like it as you cut through the stalk to pull off side tubers. This makes it easier to get your nippers in place and to make single or double tuber clumps.

I’ve outlined the two crowns I am after next. Depending on the angle, you can use your nippers to divide a couple of tubers off and then separate them. Or use a dahlia knife to carefully make a cut on either side of the crown. We prefer to separate into smaller tuber clusters and then use the nippers again to make single tubers.

Once done, you should be able to identify the mother tuber and all the new tubers. The mother tuber is often tea stained from the soil. It likely is darker and may have a rougher skin as it has survived two growing seasons. Sometimes they will be good for another growing season, but they just as often are hollow in the center and beginning to rot. As you can see below, often there are plenty of new tubers and it’s ok to let the old tuber go. If you do attempt to keep the mother, you can try a float test in pure water or water mixed with dilute bleach. If it floats, it’s rotting and needs to be tossed. You may also want to store it separate from the other tubers in case it does rot.

In the end, there is a nice pile of new tubers and the old mother tuber at the top of the screen. In 5 years, I rarely keep a mother as I find I have plenty of tubers. I divide down to clumps of one, two, or three tubers. These can easily be divided more in the spring and once eyes develop a little more, I get a good feel for where I can make additional cuts. Some of the tubers with narrower necks seem to store better in our humid coastal environment when they are in small groups.

Last, and this is important. Let the open edges heal and dry before storage. In a non-humid climate this may take 2-3 hours. In our humid environment on the coast, over night or up to 24 hours seems to be sufficient. If you divide them and then leave them for a week or more, especially in arid climates, the tubers will desiccate and wrinkle, going soft. Once you divide, you want to make sure you can put them into your storage medium the next day. Some use cinnamon on the open tissue as an antifungal/bacterial. This seems to be successful for many, but we have never had the need for this step.

Cheers and Happy Gardening (or in this case dividing).

This photo shows a clump of freshly washed tubers held up. It still has the green stalks and all the feeder roots attached to the tubers.

This image shows the tubers with feeding roots attached. There is an arrow pointing the darker mother tuber.

This image shows the rounding bulge of the crown of two different tubers and the white spots are the eyes. Eyes can be white, but may darken as they dry and go dormant for storage.

Here the feeder roots have been removed and now you can see the tubers. This image shows a feeder tuber off the mother tuber.

There are four tubers with swollen crowns and eyes. An initial cut has been made to pull two tubers off with their stalk.

A cut was made here to separate the stalks and tubers attached to that stalk.

With the first stalk removed, two more tubers with swollen crowns and bumpy white eyes are ready to be cut off the plant.

The top of the image has the old mother tuber, darker and rough skinned. The bottom of the image has tuber singles, doubles or triples separated for storage.