HARVESTING AND DIVIDING DAHLIA TUBERS
It’s important to know that there’s no single right way to divide and store tubers. Below is the method that works for me. You’ll want to experiment with what suits your lifestyle, schedule, and energy. Any method will most surely result in a few lost tubers over the winter, so don’t get discouraged if that happens.
Supplies
It’s wise to gather everything before the first frost. Below is a list of supplies I use.
Garden gloves.
Loppers to cut the stalks down to 3-6 inches.
A garden fork to gently dig up the tuber clumps.
Water and a soft toothbrush.
A place to dry them (not on concrete!) until they are no longer wet to the touch.
A pair of finely pointed snippers (bonsai scissors are excellent).
A bowl of cinnamon as an anti-fungal coating on the freshly cut ends.
Plastic wrap.
Plastic containers with lids.
A dark place to store them that is ideally 45-50 degrees Fahrenheit, with some humidity in the air.
A space where you can easily check on them every few weeks over the winter and immediately dispose of any that are rotting or molding.
Labels
It’s easy for labels to become separated from their plants, completely removing your confidence of which dahlia is which when you go to plant in the Spring. If you care about knowing which specific cultivar a plant was, you’ll want to label your dahlia plants when they are in full bloom. You’ll want these labels to be secured at the base of your plant. Flag tape is a great choice.
Timing
When to Cut Back. Knowing the forecast for your first frost and for rain will help you plan your entire digging, dividing, and storing process, which should ideally take roughly three weeks. (Though I’ve managed to stretch it out to five weeks because it’s just me dividing thousands of tubers, and they’ve come through fine.)
Many gardeners know their USDA “Zone.” From there, you can learn when your first frost usually is. A good rule of thumb for most of my clients will be to take loppers and cut their plants down to 3-6” in mid- to late October. Make sure those label tags stay put!
After you cut your plants back, you ideally want to let them “cure” for a week or two before lifting them out of the ground. During this two-week window, the roots will be feeding and strengthening the tubers instead of the whole plant.
You may have heard that it’s important to wait until the first frost to cut your plants down, but what is truly important is that you not leave them in the ground so long that there is a hard freeze. There’s nothing wrong with harvesting early. Ideally, the tubers will have been in the ground for 120 days. So if you planted them May 1, you can safely dig up your tubers in September, even. This is important because life throws us curveballs—whether it’s a vacation or an unexpected illness, you have more flexibility than you think around when you harvest.
You also don’t want them sitting in too much rain after the first frost. You want to avoid rain because they are vulnerable to rot, and also, you don’t want to be digging them up in the cold rain. Believe me. I’ve done it.
The importance of planning here will make this process much smoother for you. When you factor in your other obligations and the weather from mid-October to mid-November, you will discover an ideal window of time for you to do this work.
Digging and Rinsing
Use a garden fork to gently start to separate the clump from the soil. You’ll want to push the fork into the ground in a roughly 12” radius around the central stalk.
Use the fork as many times as you need to in order to loosen the soil enough so you can grab the cut stalk and gently pry the tuber clump out of the ground. Where you had planted one tuber, you now may see three, or ten, or over twenty tubers! Don’t worry if your garden fork has pierced a tuber—this is inevitable, and in many cases, the tuber can be salvaged.
Lift the tuber clump as a whole out of the ground. If you are not ready to divide just yet, you can keep the dirt on the clumps until you are ready to process them. I’ve done this and they’ve kept for a month just fine. I’ve heard of people storing them in their own dirt all winter! (Remember, there is no one right way. This is just my way.)
If you plan on drying, dividing, and storing right away, you’ll want to wash off all the dirt, either with the force of hose water or with a basin of some kind and a small soft brush like a toothbrush. (I’ve even heard of people using an air compressor!) Then you’ll set them aside on the ground, grass, cardboard, paper towels, terry towels—anything but concrete, which will dry them out and spoil them in the blink of an eye.
As they dry, you’ll want to keep watch. Every person’s ideal drying time will be dependent on the relative humidity where you are drying them. Some tubers will dry in a few hours, others may take a day or two. You want to catch them when they are no longer wet to the touch, but have not started to shrivel up.
Guess what? Through all of this, mind your labels! I’m telling you!
Dividing
I like to try and precisely save each tuber, but many people are willing to forego a few tubers in the interest of time. Such people will take the loppers or hoof clippers or even a power tool and quarter each clump into four smaller, more manageable clumps. You inevitably lose a few tubers, but gain time.
With either method, you’ll get to a point where you’ll need to rinse off the bits of dirt stuck in the tuber crevices. This is where a soft toothbrush comes in especially handy.
With the tubers cleaned off, trim off all of the skinny, hairy roots, and also cut off any tuber that is thinner than a pencil, or any tuber with a floppy, broken neck.
Now look for the eyes. This is where future stalks will originate from. You can find many video tutorials online that show closeups of what you’re looking for.
You need five parts of the tuber for your best success rate: 1) the body for energy storage, 2) the neck for energy transport, 3) the crown that looks like a raised ridge, 4) at least one visible eye on each crown, and 5) a wee bit of the central stalk attached to the crown. (But not too much! Possible rot conductor!) You want just enough of the stalk so that the crown has a bit of heft to it so that it’s less likely to break during storage and spring planting.
Now get in there with your finer bonsai scissors. You want to take your time for safety reasons and also to not damage the tubers.
Storage
Congratulations! You divided your tuber clump! You’re looking at several individual tubers that are probably wet because you were rinsing off dirt. So you’ll want to dry these, but they will probably dry fairly quickly, either in a few hours or overnight, again depending on the relative humidity.
A lot of people (myself included) like to dip any exposed cuts in cinnamon, which has natural anti-fungal properties.
Cut off a stretch of plastic wrap. (I know. I know! This method has given me a 95% survival rate in overwintering. I’m experimenting with compostable wrap.) Lay the first tuber on a corner of the wrap and roll it up a few turns. Then add another tuber with the crown on the opposite side and give it a few turns. Fold the sides in and continue adding tubers until you run out of plastic wrap. Pro Tip: Twist or fold the pointy end flap to make for easier unwrapping in the Spring.
Label your wrapped tubers. Some people simply tuck the tag they made into the plastic wrap. Others place each cultivar in its own plastic bin with a lid and label the outside of the bin. (I do both.)
Put them to bed in a dark place that is ideally 45-50 degrees Fahrenheit, with 80% humidity. I store mine in my apartment and keep it at 60 degrees, with humidity around 40%. (The higher temperature could lead to moisture issues, so that’s why I keep my. humidity lower.)
Check on them every couple of weeks at first, then every month. Clear plastic containers are helpful because you can more easily see condensation that might indicate a rotting tuber in the bunch. If this happens, unwrap the tubers until you find the culprit. Make sure to wipe down any condensation before putting the lid back on. You may find that you can snap the lid shut, or perhaps the air in your storage area is damp and you need to drill holes in the lid or simply tilt it at a little angle, or even run a fan to reach ideal humidity. A well-placed paper towel in a bin can absorb rogue moisture as well.
Sometimes tubers from certain plants will just rot. This often happens when the plants have been cut back, there has been frost, and there has been a lot of rain, and you left them in the ground for 3 weeks or so—the center stalk probably started to rot a bit. You’ll know it’s happening because suddenly an entire box will be plagued by moisture. It happens.
This does take time, but you will save money in the long run, and will have a gorgeous field of dahlias you can sell or share with friends!