The simplest way to explain how to overwinter dahlias is this: after frost blackens the foliage, cut the stems down, dig the tubers, let them dry, and store them somewhere cool and frost-free until spring. In mild zones you can skip the digging and mulch them in the ground instead.
Dahlia tubers are not hardy in cold ground, but they multiply year after year, so saving them is far cheaper than buying new plants. This guide covers both methods, a simple storage chart and what to do when tubers shrivel or rot.
Quick Answer: Overwintering Dahlias at a Glance
- Cold zones (6 and below): dig tubers after the first frost and store indoors.
- Zone 7: either method can work; mulch deeply or dig to be safe.
- Zones 8 to 10: leave in the ground with a thick mulch layer, if drainage is good.
- Storage temperature: about 40 to 50°F (4 to 10°C), dark and slightly humid.
- Replant: after the last frost, when soil is around 60°F (15°C).
Should You Dig Dahlia Tubers or Leave Them In?
It depends on how cold and wet your winter is. Look up your zone on the USDA Plant Hardiness Zone Map. In the UK, many gardeners in the south and in sheltered city gardens leave tubers under a deep mulch, while those with cold or heavy, wet soil lift them.
| Climate | Method | Notes |
|---|---|---|
| Zones 3 to 6 | Dig and store | Ground freezes deep enough to kill tubers |
| Zone 7 | Mulch or dig | Depends on drainage and winter lows |
| Zones 8 to 10 | Leave in ground | Add 4 to 6 inches of mulch; avoid soggy soil |
| Wet, clay soil anywhere | Dig and store | Wet winter soil rots tubers |
| Containers | Move pot to a frost-free shed | Keep nearly dry |
How to Overwinter Dahlias by Digging Tubers
- Wait until the first frost blackens the leaves. This signals the tubers to mature. Leave them in the ground another week or two.
- Cut stems down to 4 to 6 inches (10 to 15 cm) and label each variety.
- Loosen the soil about a foot from the stem with a garden fork, and lift the clump gently. The necks snap easily.
- Shake off loose soil, or rinse lightly, and let the clump dry in a sheltered spot for a few days to a week. Do not let them freeze.
- Trim thin roots and remove any soft or damaged tubers. Division can wait until spring, when the eyes are visible.
- Pack clumps in boxes or crates with slightly damp peat moss, vermiculite, wood shavings or dry sawdust, and keep them in a cool, dark, frost-free place.
- Check monthly. Mist lightly if tubers look wrinkled, and remove any with mold or rot.
Storage Materials Compared
| Material | Pros | Cons |
|---|---|---|
| Peat moss or coir | Holds light moisture, easy to find | Can stay too wet |
| Vermiculite | Clean, lightweight, absorbs excess moisture | Costs more |
| Wood shavings | Cheap, breathable | May dry tubers out |
| Plastic wrap | Stops shriveling | Needs checking to avoid mold |
How to Overwinter Dahlias in the Ground
In mild areas, cut the stems down after frost and cover the clump with 4 to 6 inches (10 to 15 cm) of straw, bark chips or leaves. Add a waterproof cover such as a tile or upturned pot over the crown if your winter is wet. Remove the mulch in spring as shoots appear. Slugs love the new growth, so protect it early.
For planting and care through the season, see our guide to how to plant and care for dahlias. You might also like when to plant tulip bulbs to fill the space once dahlias are lifted.
Common Dahlia Storage Problems and Fixes
- Shriveled tubers: storage too dry or warm. Mist the packing material lightly and move somewhere cooler.
- Rot or mold: too damp or poor airflow. Cut away soft spots, dust with sulfur or let dry, and repack in drier material.
- Early sprouting: storage too warm. Move to a cooler, darker spot.
- Broken necks: a tuber without a piece of the crown will not grow. Discard it.
Replanting Dahlias in Spring
In early spring, take tubers out and check them. Divide clumps so each piece has at least one tuber and a bit of the crown with an eye. Start them in pots indoors for an earlier display, or plant directly outside after the last frost, about 4 to 6 inches (10 to 15 cm) deep and 18 to 24 inches (45 to 60 cm) apart. Hold off on watering until shoots show, since wet soil can rot tubers that have not started growing.
Conclusion
Overwintering dahlias is mostly about timing and keeping tubers cool, dry-ish and frost-free. Dig after the first frost in cold zones, mulch in mild ones, check monthly, and replant once the soil warms. A few minutes each month saves you money and keeps your favorite varieties.
FAQ
When should I dig up dahlias?
One to two weeks after the first frost has blackened the foliage. Digging too early gives immature tubers that store poorly.
Do I need to wash dahlia tubers before storing?
It is optional. Rinsing helps you inspect them, but they must dry fully afterward. Many gardeners simply brush off loose soil.
Can I store dahlia tubers in a garage?
Yes, if it stays above freezing and below about 50°F. Insulate boxes or move them if a hard freeze is forecast.
Can I leave dahlias in pots over winter?
Yes. After frost, cut stems down and move the pot, tubers inside, to a frost-free shed or garage and keep the soil almost dry.
How long do stored dahlia tubers last?
Properly stored tubers keep for the whole winter, and healthy clumps can be divided and replanted for many years.
