Dahlias are a popular summertime flower grown for their beautiful blooms in a variety of colors, shapes, and sizes. As the end of the growing season approaches, many gardeners face the question of whether to dig up the dahlia tubers or leave them in the ground over winter.
Do you have to dig up dahlias for the winter?
Dahlias are not winter hardy in most climates and will not survive freezing temperatures in the ground. The dahlia tubers, stems, leaves, and flowers will die back with the first fall frost. If left in the ground through the winter, the tubers will rot and decay.
For this reason, it is generally recommended to dig up and store dahlia tubers over the winter in climates with freezing temperatures. If you want to replant the same dahlias the following spring, they will need to be dug up and properly stored indoors over the winter.
What happens if dahlias are left in the ground over winter?
If dahlia tubers are left in the ground over winter, they will be exposed to freezing and thawing cycles as well as increased moisture. This leads to the tubers rotting away by springtime. The tubers will not survive the winter to sprout new growth in spring.
Specifically, here is what will happen over the winter if dahlia tubers are left in the ground:
- The above ground plant parts die back after the first hard frost in fall.
- The tubers are subjected to freezing and thawing as winter temperatures fluctuate.
- Excess moisture in the soil leads to rotting of the tubers.
- Tubers start to shrivel up and decompose over the winter months.
- By spring, only mushy remnants of the tubers will remain in the ground.
- No viable tubers will be left to sprout new dahlia plants in spring.
Will dahlias survive the winter if mulched?
Simply mulching dahlia tubers in the ground will not provide enough protection for them to survive the winter in climates with freezing temperatures. The insulation from mulch may help protect against minor cold snaps, but will not prevent the soil from eventually freezing.
Once the soil freezes, the dahlia tubers will freeze as well. Alternate freezing and thawing will damage the tuber. Excess moisture under the mulch can also lead to rotting over winter. Leaving the tubers in the ground over winter, even if mulched, results in death of the tubers in most cases.
Can you leave dahlias in pots over winter?
Dahlias left growing in pots can also be damaged or killed over winter if left outdoors. Potted dahlias should be treated similar to those growing in garden beds.
Pots provide insulation to the roots, but once the soil freezes, tubers left in pots will also freeze. The freeze/thaw cycles will damage the tuber. Additionally, excess moisture from rain or snow can accumulate in pots and lead to rotting.
Potted dahlias left outside over winter will likely not survive just like those left in the ground. They need to be brought indoors and stored properly for the winter.
Storing dahlia tubers over winter
To save dahlia tubers for replanting the following year, they need to be dug up in fall and stored over winter protected from frost. Here are some tips for overwintering dahlia tubers:
- Dig up tubers after first frost when stems are damaged.
- Cut stems back to about 6 inches.
- Brush off excess soil but don’t wash tubers.
- Allow to dry out for a few hours before storage.
- Sort by viable healthy tubers and discard any rotted ones.
- Pack in peat moss, vermiculite, or wood shavings.
- Store in a cool, dark place like a basement or cellar.
- Ideally keep at 40-50°F over winter.
- Check periodically for rotting and discard affected tubers.
- Replant the following spring after danger of frost has passed.
Proper care when digging up and storing the tubers will result in healthy dahlia plants that can be replanted for the next growing season.
Reasons some choose to leave tubers in the ground
Given that dahlia tubers rarely survive winter conditions in the ground, why do some gardeners choose to take the chance and leave them in place?
Here are a few reasons why you may want to experiment with leaving dahlias in the ground:
- Leaving tubers in place saves the work of digging them up and replanting in spring.
- Some varieties are cheaper and not worth the storage effort.
- You have an abundance of tubers and are willing to sacrifice some.
- Your climate experiences occasional mild winters.
- You forget or run out of time to dig them up.
- You don’t have a good place to store the tubers over winter.
- You want tubers to naturalize in the garden.
While leaving dahlia tubers in the ground is risky, gardeners may opt to do so for the reasons above or just to see if they happen to survive.
Locations where dahlias may overwinter
While dahlias are not winter hardy in most climates, there are some locations where they have a better chance of making it through the winter in the ground:
- Warmer coastal climates like the maritime Pacific Northwest, parts of Europe, and British Columbia. The winter temperatures are more moderate and the ground rarely freezes.
- Southernmost USDA zones 8 and 9. Areas like southern Texas, Arizona, south Florida and California. Winters are typically brief and mild.
- Microclimates with protection from wind, frost pockets, heat reflection off structures, and proper drainage.
- Periods of drought winter where the ground stays frozen can help prevent tuber rot.
- Heavier mulching provides insulation and drainage.
- Raised garden beds or mounded soil improves drainage.
While not guaranteed, dahlias left in the ground through winter have a higher survival rate in these types of locations.
Caring for dahlias left in the ground
If you choose to experiment with leaving your dahlia tubers in the ground over winter, here are some tips to give them the best chance of survival:
- Wait until after the first frost to cut back the stems to about 6 inches.
- Mound soil, compost, or mulch over the tubers for insulation.
- Add extra mulch as additional insulation if extreme cold is expected.
- Cover the bed with leaves, straw, or evergreen branches for protection.
- Surround with a mesh cage to prevent rodent damage.
- Ensure the tubers are in well-draining soil or raised beds.
- Water the soil thoroughly in fall and allow it to drain fully before ground freezes.
- Uncover beds in early spring to allow soil to thaw and dry out.
- Watch for sprouts to emerge when soil warms up.
- Be prepared to replace tubers if none survive.
Even with the best care, there is no guarantee dahlias will make it through winter in the ground. But taking these steps can increase your chances of success.
Signs of survival
If you left your dahlia tubers in the ground, watch for these signs in spring to see if they survived:
- New sprouts emerging from the ground as soil temperatures rise.
- Leaves appearing above ground when sprouts reach 3-4 inches tall.
- No signs of rotting or mushy plant material where tubers are located.
- Firm tubers still intact when checking below the soil surface.
- Tubers resume growing larger as sprouts continue to develop.
You will know fairly early in spring if your dahlias survived the winter based on this new growth. If no sprouts appear, the tubers likely succumbed to the cold weather.
Caring for dahlias after winter
For dahlia tubers that do make it through winter in the ground, resume normal care when spring arrives:
- Fertilize the soil to replenish nutrients.
- Water regularly as the weather warms up.
- Watch for pests and diseases.
- Pinch out the center sprout to encourage branching.
- Stake plants as they grow taller.
- Deadhead spent blooms to promote more flowers.
The tubers that survived over winter should be stronger plants in spring. With proper care, they should flourish and produce another season of beautiful dahlia flowers.
Reasons dahlias may not survive
If your dahlias failed to come back in spring despite your best efforts, here are some reasons the tubers may have perished over winter:
- Extreme cold temperatures reached the depth of the tubers in the ground.
- Frequent freeze/thaw cycles caused damage.
- Excess rain or snow led to tuber rotting.
- Lack of drainage in the site allowed water to pool.
- Mulch or soil mounding didn’t provide enough insulation.
- Rodents like voles chewed through the tubers over winter.
- The tubers froze and didn’t receive enough protection.
- Preexisting disease such as bacterial soft rot spread through the tubers.
Even if you followed best practices, the winter conditions may have simply been too harsh for the dahlia tubers to survive in the ground. When in doubt, always dig them up instead of chancing a loss.
Replacing tubers that didn’t make it
If your dahlias didn’t make it through the winter, all is not lost. You have a couple options to still enjoy those favorites again next year:
- Buy new tubers – Visit your local nursery or online retailer to purchase replacement tubers of the same varieties you lost.
- Divide existing tubers – If you have any viable dahlias left, you can divide their tubers in spring to propagate more plants.
- Take cuttings – For some dahlia varieties, you can take cuttings off new sprouts and root them to generate new plants.
With a little effort and expenditure, you can rebuild your dahlia collection even if your tubers met an untimely end over the winter.
Key takeaways on leaving dahlias in the ground
Here are the key points to understand when it comes to leaving dahlia tubers in the ground over winter:
- Dahlias are not winter hardy in most climates and will die back after frost.
- Leaving tubers in the ground often causes them to rot and decay over winter.
- Milder climates increase chances of survival when left in the ground.
- Take steps to insulate and protect tubers if attempting to overwinter them.
- Check for sprouts next spring to see if tubers survived.
- Be prepared to replace tubers that don’t make it through winter.
While not usually recommended, leaving dahlias in the ground can work in some scenarios. Just be aware that you risk losing your tubers and may end up buying replacements come spring.
Conclusion
Dahlias brighten up gardens with their late season blooms, but require some extra care when it comes to handling their tubers through winter. Tubers left in the ground through winter often rot and die off. While gardeners may get lucky in milder climates, the safest approach is carefully digging up tubers and storing them properly indoors until spring planting time returns. With a little diligence in fall and tender care in spring, dahlia tubers can reemerge reliably for many years of beauty.
