My aunt is a dahlia breeder, avid grower and exhibitor of prized dahlias in Whatcom County, WA. Many of my favorite childhood memories include my cousins and I playing in her 7-acre dahlia farm while our parents sat and talked in her glass greenhouse or around a bonfire. Dahlias seem to be a family pastime, if not obsession.
Even with an “expert” in the family my mom and I learned a lot through trial and error. We stored the clumps uncovered and unprotected in our well’s pump house each winter, losing many tubers and entire clumps as they were alternately too dry or too moist. A few years back my aunt told us about a new technique where growers were dividing their tubers in the fall and then wrapping each variety in plastic wrap, keeping a layer of plastic around and between each tuber. The logic was that if one tuber rotted it would be segregated from the other tubers and that the plastic wrap protected the tubers from desiccating. We have used this method for four seasons now and it works well! However, the quest to continually improve storage methods and reduce waste continues.
Some areas of the world where winter temperatures rarely go below freezing (USDA zones 9-10) don’t have to dig their dahlia tubers in the fall. Some growers in zones 7-8 heavily mulch their plants and leave the tubers in the ground over winter, too. Here in Bothell, WA, which is located about 30 minutes north of Seattle our winters are wet, wet, wet. My soil is heavily clay-based, which increases its ability to hold water. Therefore, I dig my tubers so they don’t rot in the ground over the winter.
The digging process begins before my first frost. All throughout the growing season I’m making notes about my dahlias and am keeping track of their names. When I plant them, I make a map of where each variety is in my garden/yard. They all have plant picks with their variety names on them written in grease pen. I use the corral method for staking them instead of giving each plant its own support structure. The resulting “corral” of string provides an easy spot to hang a marking tape with the dahlia variety name on it, preventing me from digging at the base of the plant to “remember” the variety name mid-season! I keep those tape markers and tie them to the base of the plant before the first frost. I try to make sure I have a photo of each of my dahlia varieties so I can more easily remember the ones I really loved, ones I don’t want to grow the next season, and ones that were diseased or attracted pests more than the others.
A side note on sanitation: we recently learned about the dahlia virus, a group of plant viruses that strike the dahlia plant as it is growing. These viruses live in live tissue (plant, flower, stems, and tubers) and are spread through contact. Thankfully, the viruses are killed through contact with soapy water solution and through a light bleach solution. I’ve started keeping an up-cycled cottage cheese container with soapy water with me in the garden. Using 2 snips/shears I keep one in the solution and then swap when I switch to harvesting or cutting a new plant. That way I stop any transmission from a potentially infected plant to a healthy plant. I also dip my knife and shears/snips between clumps of dahlia tubers when I divide in the fall. For more info on the dahlia virus, I recommend the American Dahlia Association’s website and the Sustainable Flower Farmer’s podcast episode on dahlia virus.
After your first frost (or late October, whichever comes first), cut back the dead/green growth to just above soil level and above your marking tape/label. Leave them in the ground for 3 days to one week so they can get their tubers ready for storage (the plant will redirect its energy into the tubers making the eyes easier to see).
Dig with a garden fork, gently lifting the clumps from the soil.
I wash the soil off the clumps as it lets me see the eyes better and I divide my tubers in the fall. I've dug all of my tubers and washed them all in one day and then I usually divide them a couple days later. Some growers dig, wash & divide all in one day!
I then divide my tubers, trying to make sure there is at least one eye on each one I cut.
I cut all the tubers I can from each clump, but if you don't intend to share or sell your tubers you can keep as many as you want and compost the remaining ones. Floret, Santa Cruz Dahlias, Triple Wren Farms, the American Dahlia Association and many more have resources on how to dig, store & divide tubers. I let my tubers dry for a day or so--until the cut part is dry to the touch--and then wrap them in plastic wrap. Pulling a long piece off the roll, I wrap one completely and then tuck another in, rolling the tw
o together with wrap separating them. I also wrap my tag for that variety after the last tuber has been "jelly rolled" in :) Then store in an area that stays 40-55F for the winter. They don't like to be too warm or they'll sweat/mold/grow and they will freeze if they're too cold (32 and below) and then turn to mush.
This fall I am experimenting with three other ways of storing tubers – in a
paper bag with pine shavings, in a plastic tub with pine shavings and in a
plastic tub with potting soil. Next spring I'll know if any of them work better than
plastic wrap! I also discovered a recycle facility for plastic wrap (after I am done with it and clean it) so I feel slightly less wasteful using the cling wrap now that I have a way to recycle it!
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