If you grow dahlias and live in a cold climate, you’d do well to learn how to overwinter dahlia tubers. With their remarkably colorful, large blooms, it’s no wonder that dahlias cost as much as they do, and buying new ones each year is simply not possible for most gardeners. Fortunately, with a little elbow grease and some attention to detail, you can successfully overwinter these Central American beauties in your attic, basement, garage, or similar frost-free place and then bring them out of storage for re-planting in your garden next year. You’ll find lots of helpful advice below on how to overwinter dahlia tubers.

Why save your dahlia tubers

Averaging about $10 per tuber, filling your cut flower garden with dahlias can really add up. That’s why knowing how to overwinter dahlia tubers just makes sense. Financial reasons aside, you also might want to store dahlia tubers that have performed especially well in your garden. Or you might choose to save varieties that are somewhat difficult to find from year to year. (Some fantastic dahlia types to look for include “The Big Wow,” “Bodacious,” and “Autumn Sunburst.”)

Another reason to save your dahlia tubers? One day you might want to divide a particular tuber clump to share with others or to multiply your own dahlia numbers. (Pro-tip: If you have more than one kind of dahlia in your garden, label the plants before their foliage dies back so that you’ll be able to tell them apart when it’s time to put them in your storage area.)

How to overwinter dahlia tubers indoors step by step

Ready to find out exactly how to overwinter dahlia tubers? Although you may come across some slight variations in what’s recommended, the following five steps for how to overwinter dahlia tubers are fairly tried-and-true. To start, you’ll need a shovel, hand trowel, or garden fork, a sharp knife, hand pruners, or loppers, some mulch material, and plastic bins, bulb crates, or clean, dry cardboard boxes.

Step 1: Dig up the tubers

The magic of dahlias stems from their underground tubers. (These contain the energy needed to start next season’s flower show.) You’ll find clumps of tubers growing about six inches below ground level. When the first frost of the season hits, your dahlias’ above-ground foliage will blacken and die back. Use loppers or pruners to cut the dahlia stalks and leaves back. Leave just two or three inches of stalk intact. As long as additional freezing isn’t in the immediate forecast, you can give your dahlia tubers a couple of weeks to toughen up underground before you dig. (But if freezing temperatures are in the forecast, don’t wait!)

Using your shovel, hand trowel, or garden fork, carefully dig into the soil near the dahlia tubers. You don’t want to get too close, as you can easily knick or cut the delicate tubers. Once you’ve lifted out the clumps of dahlia tubers, it’s time to remove the excess dirt from them. You can either gently spray them off with a garden hose or keep the dahlia clumps dry and gently brush away the extra soil with your hands.

Step 2: Handle the tubers with care

Examine each tuber clump for signs of damage or disease. If you see that some tubers have begun to rot, separate these from the others and discard. You should also cut away any badly damaged areas you notice. Next, place your dahlia clumps upside-down inside open paper bags or cardboard boxes. Store these in a dark, cool place for about a week. (This will allow trapped moisture to drain out of what remains of the central stalks.)

After this drying period has passed, use garden shears or a clean, sharp knife to trim the stalks back to about an inch long. Now the tubers are ready to pack up for the winter.

Step 3: How to pack dahlia tubers for overwintering

When it comes to packing the tubers, you have several good options. You can simply wrap each tuber clump in newspaper or a paper bag and then pack these into cardboard boxes or bulb crates. Alternatively, you can line your storage boxes or crates with newspapers, heavy craft paper, or burlap, and then layer the clumps of tubers in a medium like peat moss, vermiculite, sand, or even very fine wood shavings. If your storage area is a little on the dry side, you may want to very lightly mist this packing medium.

Step 4: Where to store the box of tubers

The longterm storage area you choose for your dahlia tubers could be an out-of-the-way closet, attic, garage, basement—anywhere that stays cool and dark. Ideally, the temperature should remain between 40 and 50 degrees F (4.4 and 10 degrees C) with about 70 percent humidity. 

Wherever you put them, do look in on your tubers periodically. If you notice signs of mold, your storage spot likely is too humid. You may need to choose a different location or try to adjust the humidity levels with a dehumidifier. If, on the other hand, your tubers look exceptionally dry or shriveled, conditions may not be moist enough. Use a spray bottle to lightly mist overly dry tubers.

Step 5: What to do with your dahlia tubers in the spring

Adhere to this sure-fire method for how to overwinter dahlia tubers and your dahlias should be raring to go again by springtime. To be on the safe side, don’t plant your dahlias in the garden until the soil has warmed up. Also wait until your average last frost date has passed. Want to give your dahlias a little head-start? You can always re-start them indoors in nursery pots during very late winter or early spring and then plant them outside once the coast is clear.

How to overwinter dahlia tubers in the garden for warm-climate gardeners

The instructions regarding how to overwinter dahlia tubers are a little different for gardeners living in a warmer climate. If you live in USDA Plant Hardiness Zone 8 or greater, you can usually get away with leaving your dahlias in place. Overwintering dahlias in these areas is as simple as cutting back the foliage and then adding a layer of bark or other protective mulch over the garden bed. Your dahlias will naturally begin to do their thing again in spring.

More tips for saving dahlias over the winter

Dahlias grow perfectly well when planted in large containers. If you’re an avid container gardener, you can overwinter dahlias in their pot. However, you’ll need to move and store it. Rather than dig up and remove potted dahlia tubers, you need only let the first hard frost hit your potted plants and then trim back the frost-killed foliage. Next, move all pots into a suitably cool, dark area for winter storage. There’s no need to water—just let your potted tubers rest. When the danger of frost has passed next spring, you can put your dahlia containers back outside.

A recap of how to overwinter dahlia tubers

Having learned how to overwinter dahlia tubers, now you should be in good shape for next season. Remember, if you live in Plant Hardiness Zone 8 or below, you’ll likely need to baby your dahlias. A big part of understanding how to overwinter dahlia tubers successfully includes digging them up without damaging them, allowing them time to cure, and then packing and storing them appropriately. Dahlia tubers keep best in a cool, dark spot—think 40 to 50 degrees F and roughly 70 percent humidity. By protecting these valuable tubers, you can save money and grow bigger, more robust dahlias—suitable for splitting and sharing—year after year.

For more in-depth advice on overwintering plants from your garden, check out these articles:

• 4 ways to overwinter tomato plants
• Overwintering hibiscus: Tips for success
• Learn how to overwinter geraniums: 5 easy methods
• How to overwinter pepper plants