For many gardeners, dahlias are the superstars of the garden. Big, beautiful, long-blooming, and rich in a rainbow of colors, dahlias make summer to fall a colorful ball. And with just a little special care, the dahlias that made this summer special can come back next year to do an even better job.

Dahlias by Marie Woodward

Proper winter care of the tuberous roots of dahlias (which for this blog we will just refer to as tubers) will determine their success in the growing season. With careful preparation and regular vigilance, gardeners can enjoy this year’s dahlias for many years to come. Just follow these sometimes surprising instructions:

First, don’t dig up dahlia tubers until after a killing frost. Tubers can be left in the ground from a few days up to a few weeks after the frost as long as the ground itself doesn’t freeze. The longer you leave the tubers in the ground the larger the eyes (growth buds) will swell, making the plant’s tubers easier to divide. A good indicator it’s tuberous root digging time is when the flowers die and turn brown. 

Dahlias blackened by frost. Photo: The Martha Blog

When you are ready to dig up the tubers (they’ll be in clumps), use a pruner or lopper, and cut the plant’s stem to about 4 inches above the ground. The stem will serve as a handle to help lift the tubers out of the soil. Next, using a long shovel or garden fork, (the latter is preferred), dig a circle around the plant about one foot away from the stem. Dig deep, and gently lift the tubers up to the surface from below the plant. If you had stuck labels in the ground when planting dahlias, be sure to keep the label with the roots so you know what you are planting where next year.

Holding the stem, shake any loose soil off the tuber clumps. Then rinse them gently with water. (A clean tuber is a happy tuber.) This can be done with a garden hose or in utility sink. Leave the tubers to dry, but for no more than 24 hrs. Caution; Don’t let them dry to the point of wrinkling (a sign of dehydration) which could cause damage to the tuber. Also don’t leave them to dry outside in freezing weather.

After they dry, carefully inspect each tuber clump. Trim any roots growing from the end of the tubers. If one or more tubers in a clump are damaged or show signs of rot and cut the affected tubers off. Such damaged tubers can spread rot to other tubers. (think of that one bad apple – thanks, Osmond Brothers).  

Once the clumps are dry and inspected, cut the stem (your former handle) low enough so it’s not hollow and make sure it’s free of any rot.

At this point you must make a decision. Some gardeners like to divide tubers in the fall (to increase the number of dahlias they have) because they are easier to cut. However, it’s hard to see the “eyes”- the swelling that shows where next year’s growth will come from – in the fall. A tuber without an eye will never flower That’s why other gardeners prefer to wait till spring to divide their tubers when the eyes are swollen. The plant is more difficult to divide after winter hardening, but in spring the eyes are easier to see. 

Whichever you decide, carefully consider the pros and cons of each approach.

After the tubers are dug out, rinsed off, dried, and inspected (and perhaps divided), it’s time to make a nice bed for them to sleep in through the winter. Almost any non-plastic container will do so long as it’s not airtight.  Plastic containers are not a good choice because they won’t provide circulation. Cardboard boxes or a crate will do just fine. 

Dahlias tucked in for the winter. Photo: Dahlias.com

Line the bottom and sides of the box or crate with about 8-12 layers of newspaper. (Burlap is another good choice if newspaper is difficult to come by.) Then, choose a medium to nest the tubers in. Freshly purchased peat moss, pine shavings, or coarse vermiculite are all good choices. The American Dahlia Society even suggests wrapping tubers in saran wrap:  https://www.dahlia.org/docsinfo/articles/no-fuss-store-your-tubers-in-plastic-wrap/

No matter what medium you choose, it’s critical that it be moist without being wet. A five-gallon bucket of vermiculite mixed with one cup of water, for example, will give tubers an ideal moisture content for storage 

Line the bottom of the box with medium and nest the tubers or clumps of tubers in the mix, giving them plenty of space between each clump. If the box is deep enough, you can layer the clumps but, make sure you have plenty of medium between the layers. Next, cover the tuber layers with the medium, and cover the medium with paper bags to keep light out. Store tubers on a shelf in an area with a temperature between 40-50 degrees.  It’s very important not to let the tubers freeze. Freezing will destroy them.

 Also, DO NOT store tuber boxes or crates on cement. Cement will draw moisture out of the medium and dehydrate the tubers. Check your tubers about once a month. If they show any sign of shriveling, spray the clumps and medium lightly with water and keep an eye on the temperature. One trick to help monitor temperature is to keep a spray bottle next to the tuber box. If the bottle shows signs of frost crystallizing, move the box to a warmer area. You can also monitor temperature using a remote wireless thermometer. Keep your dahlias dry, unfrozen, and in the dark till spring, and you’ll be ready for a dahlia explosion in the summer to come. The process of preparing dahlias for winter is not hard. It just requires more steps to ensure success for the next growing season. I’m sure, like me, you will find the reward of seeing your dahlias blooming happily in the garden well worth the winter effort. 

Marie Woodward