Dahlias are one of my favorite flowers to grow. There is something about their magnificent sizes and colors that just make me happy every time I see them. Dahlias are easy to grow, come in a variety of colors, and if cared for correctly, you can dig, divide and replant the dahlia tubers year after year for more and more blooms.
Today I am going to teach you the basic steps to prepare your dahlia tubers for winter storage, so they are ready to plant next spring!
What Are Dahlia Tubers?
It’s pretty simple! Dahlia tubers are the root of the plant. They grow in clumps right below the surface. They look like this:
When to Dig Up Dahlia Tubers
In most parts of the US and Canada, winters are too cold to leave dahlias in the ground. Plus, even in zones where they would over winter it’s still advisable to dig and divide your tubers, so they don’t become too large and unmanageable.
After blooming is complete for the season, and you have seen the first 1-2 frosts, it is time to dig up dahlia tubers and store them for the winter.
TIP: Make sure to label your plants BEFORE the frost. Within the first 24 hours after the first frost blooms, stems and all that beautiful greenery turns brown and black, and you won’t be able to distinguish one from the other.
Wait at least 1-2 weeks after the first frost to dig your dahlias. That frost stimulates the tubers and helps them grow “eyes,” which will become their main flower stems for next year. Be sure to get them out of the ground before it freezes because that is what will cause damage to them.
Digging Dahlia Tubers
The first thing we do before digging is cut back the old plant stems down to about 6-8″ above the ground. Then we clean up all the debris tossing it into the compost pile. This makes it much easier to see what you’re digging and makes the tuber clumps easier to handle.
To dig up dahlia tuber clumps we use a pitch fork to gently lift them out of the ground. Be as careful as you can not to nick or chop tubers but don’t beat yourself up too much if you lose a couple—it’s to be expected.
We place the pitch fork into the ground about 6-8″ away from the growing stem. Gently dig the pitch fork into the earth and then start to angle it, your goal being to get underneath of the tuber clump, clear of any deep tubers. Wiggle and shake with the pitch fork as you gently lift from underneath the dirt-filled tuber clump. Sometimes you need two people for this part!
Download my FREE Dahlia Grow Guide below!
The guide includes everything you need to know from planting to caring for to harvesting to vase life tips to digging, diving and storing dahlia tubers plus my sources for buying the best tubers!
Cleaning & Prepping Dahlia Tubers
After digging we gently brush away and shake off any excess soil and then bring them over to the work table to wash all the soil away. This is when we also prune off any long, straggly roots and any tubers that are thinner than a pencil.
At this point you could actually also divide clumps into individual tubers, the eyes are super prominent and easy to spot. The only thing is storage gets a little tricky on fresh cut individual tubers. More advanced growers do it this way but as a beginner its best to store the full clump together over the winter and divide in the spring.
After washing and pruning we allow the tuber clumps to cure, or toughen up, for a few days. Then it’s time to pack them away in their storage crates.
To help prevent rotting during the winter, I highly recommend sprinkling sulfur dust, a fungicide and insecticide, on dahlia tubers before storing them. Sulfur is important because acts as a fungus deterrent. The dusting can be extremely light but try to cover as much of the tuber as possible, especially wherever there may be a nick in the skin.
Storing Dahlia Tubers
We store tubers in bulb crates or plastic bins filled with sawdust, vermiculite or a similar medium. These mediums help to keep just the right amount of hydration, so the tubers don’t rot but also don’t shrivel from dryness during storage. I have even heard of some people saran-wrapping individual tubers—I have too many to make this method worth it but let me know if you try!
Dahlia tubers like being stored in a dark room, between 40-50 degrees and at about 80% humidity all winter. Make sure to label your varieties (we label twice because tags sometimes get lost in the shuffle!), check tubers monthly for rot or dryness and adjust the humidity accordingly.
Winter Care Tips for Dahlia Tubers
During the winter, check on your tubers monthly for their moisture levels. Too dry and the tuber will shrivel and waste away. Too wet and it will rot. If they are shriveling and looking dry, you can spritz your storage medium with water in a spray bottle. Surprisingly, I’ve seen many shriveled, dead looking tubers come back to life in the spring so don’t toss these ones too soon!
In my experience, rot occurs more often than tubers becoming too dry during storage. You can tell if the tubers are rotting if they become mushy or there is visible mold. If they become rotted, toss them out before they can spread the rot to the others.
How to Divide Dahlia Tuber Clumps
Dividing dahlia tubers is a lot of work but it gives you the best bang for your buck. During the growing season, your dahlia plant is not only producing many beautiful blooms above ground, but also many beautiful, swollen roots underground. It always amazes me that I can plant one single tuber in May and dig up a clump of 5-10 more hanging off just that original one!
You can either divide before storing or after. More experienced gardeners can divide before but as a beginner I would wait until early spring to divide. The eyes become much more visible and pronounced as spring approaches so it’s easier to know you’re cutting in the right spot!
To split large clumps, I first cut them straight in half with sharp pruners. This will leave you with two smaller dahlia tuber clumps.
Once you have cut the tuber clumps in half, it’s easier to divide them into individual tubers. First, you need a super sharp and super clean and sterilized knife. The key to a viable tuber is making sure that it has at least one eye (located on the main crown) and an unbroken neck (the part connecting the tuber to the crown). This is why, until you gain experience, it’s easier to wait until spring to divide so you can clearly see the eyes.
I hope I’ve motivated you to elevate your gardening skills and take the next step by digging up and dividing your dahlia tubers. Yes, it does take a little extra energy and care but think of how many more dazzling blooms will adorn your gardens in the spring! I promise you it is totally worth it!!