While Dahlias cannot survive the winter in a cold climate garden, you can dig up the tuberous roots in fall and store them (overwinter) until it’s time plant them again in spring.
For detailed growing tips, see How to Plant and Grow Dahlias.
How to Store Dahlia Tubers for the Winter
Timing
Dahlias are perennial but not hardy below USDA hardiness zone 8 so our workaround is to ‘overwinter’ them.
Lookup United States Hardiness Zones | Canadian Hardiness Zones
Overwintering simply means storing them in a dormant state for winter where the freezing temperatures cannot harm them.
And that means removing the tubers from the ground as first fall frosts set in and keeping them safe in storage.
- During the growing season pay attention to which of your dahlias do best and those that are meh or under-performing.
- Mark the best ones as candidates for winter storage. I use pieces of ribbon tied to their supports to indicate the keepers. A meh tuber is not going to improve next year.
In fall, keep your dahlias growing until the plant has blackened from a few good frosts if you can.
It’s always a juggle to get things done before the freezing temperatures set in, but the initial cold benefits the tubers.
More Dahlia Growing Tips
Overwintering Dahlias in the Ground
Depending on your growing zone and how cold your winters get, you may be able to leave your tubers in the ground for the winter.
Success will depend on a whole bunch of factors including the variety you are growing and how wet and cold it gets.
When I lived in zone 5, I kept my dahlias (variety unknown) in the ground all year-round. To further insulate them in the winter, I covered the area with a foot of straw mulch and they were situated in a well-draining area. This was enough to prevent freezing.
If your ground doesn’t freeze deep down, in-ground storage (leaving the tubers in place) may work. Otherwise, dig them up.
Digging Up Dahlia Tubers
At the end of the growing season, as fall frosts begin, some growers trim off all but about 6-inches of the main stem and wait a week or two longer before digging them up.
Use a spading fork to ease the tubers out of the ground. It’s much like digging up a crop of potatoes. Work at least a foot away from the plant and dig deeply to avoid any chance of injuring the tubers.
At this stage, your single tubers have probably multiplied (yay) and they may emerge from the soil as a bunch all joined together.
Get them out of the ground and prepare them for storage.
Related: How to Overwinter a Potted Tree
Preparing Tubers for Storage
This is another topic where there are as many methods as there are gardeners. Read all the way through to understand why tossing them in the cold room, like our grandparents used to do, may or may not work.
Keep in mind that your tubers may also benefit from dividing before storage.
Storage Prep
Sterilize your gear and wash your hands before handling them to avoid spreading disease.
- After digging up tubers, remove excess soil without causing any damage to the tubers.
- Reduce the stem length to an inch, trim away any roots and unhealthy pieces.
- Divide tubers as needed.
- Optional: bleach treatment or fungicide application.
- Allow time to air dry (a few days), and store them.
Some gardeners just tap off the excess soil before and after air drying, others wash the entire tuber in water and brush away all traces of soil.
Some gardeners also treat the cleaned-up tubers with fungicide or dip them in a 1:10 bleach/water solution.
You always want to discard any dead, damaged, or diseased tubers and just keep the good-looking ones.
Dividing Tubers
You can divide tubers now—before storing them—if the eyes are visible. The video shows helpful examples.
The other option is to divide them in spring but be forewarned that some tubers toughen up so much over the winter that they can be very difficult to slice.
I’m a do-it-now person if the opportunity is there.
Storage Options
“But my grandparents just tossed the tubers in a paper bag and stashed it in the cellar and that worked fine….”
Yes, that easy method can work but only if other conditions happen to be optimal—things we don’t think about if everything is going well.
The optimum storage temperature is between 40-45°F (4-7°C) with medium to high humidity.
The goal is dormancy in a cool, dark place.
Too warm or dry and they may wither or rot. If they freeze, they do not survive.
Even if you provide excellent storage conditions, about 10% of tubers will not grow again, depending on the variety. The plastic wrap method (below) seems to do best with approximately 95% regrowing.
1Plastic Food Wrap Method
Wrap each tuber individually in plastic food wrap, label with names on affixed pieces of tape, place in box one inch apart and store. You can also write the name directly on the dry tuber with a permanent marking pen.
2Paper Bag Method
Place loose tuber or clump of tubers in one bag each and store.
3Newspaper Method
Wrap each tuber or clump in newspaper, store without touching others.
4Container Method
Place tubers (not touching each other) in container filled with any of the following:
Coarse vermiculite, wood shavings for pet bedding, dry (disease-free) leaves, or moistened sand. Peat moss used to be an option but its use is no longer recommended for environmental reasons.
If humidity level is low, cover with lid with air holes.
Maintenance
Check your tubers every few weeks and discard anything moldy or shrivelled. I set a reminder on my phone for this.
If conditions are too dry, add moisture. One way is to put an open jar of water in the store bin.
Spring
As outdoor conditions begin to warm, your storage area may too.
Eyes will begin to develop as the tubers warm up. Be sure tubers do not dry out.
Start your dahlia tubers indoors 4 to 6 weeks before last frost or wait and plant directly outdoors after risk of frost has passed.
Can I Still Grow a Shriveled Dahlia Tuber?
Sometimes. So long as it is not diseased, it is sometimes possible to re-hydrate a shriveled dahlia and grow it as usual. You’ll likely know by looking at it if it is too far gone.
To re-hydrate a tuber:
- Wrap the tuber in a moistened paper towel (not dripping wet) and sit it in an open food bag or container in a warm location like a kitchen cupboard.
- Check daily to see if it is plumping up again. Give it two weeks to recover.
Resources
- Dahlia Societies and Conferences | Canada and United States
- Dahlia Databases and Suppliers | Dahlia Addict (North America)
- Dahlia Research | Researchgate.net
- No Fuss Plastic Wrap Storage | The American Dahlia Society
And that’s a wrap. Go grow some dahlias!
And be sure to sign up for the free creative gardening newsletter for more tips and ideas.
~Melissa the Empress of Dirt ♛
How to Overwinter Dahlias
Supplies & Materials
- 1 Dahlia
Equipment
Instructions
- After first fall frost, trim dahlia stem down to 6-inches tall.
- In the next week or two, carefully dig up tubers using a spading fork.
- Lay tubers out to dry for a day in a sheltered location then gently brush off excess soil.
- Apply bleach treatment (1-part bleach: 10 parts water) or fungicide if disease is a concern.
- With clean scissors, trim away any dead, damaged, or diseased pieces or roots.
- Divide multi-tubers if desired.
- Wrap each tuber in plastic food wrap or paper bags and label with name.
- Store in cool, dark location with temperature of 40-45°F (4-7°C) at medium to high humidity
- Check monthly and discard any rotting tubers.
- Plant indoors in containers 4-6 weeks before last frost to prepare for transplanting outdoors after last frost.
