Digging and Storing Dahlia Tubers After Frost
In Zones 3 through 7, dig dahlia tubers about one to two weeks after the first frost blackens the foliage, let them dry for a day or two, then store them in barely damp peat moss, vermiculite, or wood shavings at 40 to 50°F until spring. In Zones 8 and warmer, dahlias can usually stay in the ground with a thick mulch, as long as the soil drains well.
The two things that ruin stored tubers are rot from too much moisture and shriveling from too little. Everything in this guide is about steering between those two.
Why wait for frost before digging
- Frost signals dormancy. A killing frost stops top growth and tells the tubers to finish ripening their skins.
- The wait toughens the skin. One to two weeks in cold soil after frost helps the tuber skins set, which reduces shriveling in storage.
- Eyes become easier to see. By late fall, the growth buds at the crown are visible, which matters if you plan to divide.
- Digging too early shortens storage life. Immature tubers dug in September tend to wrinkle by January.
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- After frost blackens the plants, cut stems to about 4 to 6 inches and label each clump by variety.
- Wait one to two weeks, then loosen soil in a wide circle with a digging fork about a foot out from the stem.
- Lift the clump gently from underneath; do not pull by the stem, which can snap the neck.
- Rinse or brush off soil and let clumps dry upside down for a day or two in a frost-free spot.
- Divide now or in spring; each division needs a piece of crown with at least one eye.
- Pack tubers in bins with barely damp peat moss, vermiculite, or shavings, not touching each other.
- Store at 40 to 50°F and check monthly for rot or shriveling.
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Should you divide dahlia clumps in fall or spring?
Both work. Fall division is easier because the tubers are softer and the soil washes off cleanly, and divided tubers take less space in storage. Spring division is easier on beginners because the eyes have swelled and are easy to spot. If you divide in fall, use a clean, sharp knife or pruners, work on a stable surface, cut away from your hands, and wear gloves. Discard any tuber with a broken neck, since it will not sprout.
Where should you store dahlia tubers?
An unheated basement, an insulated garage that stays above freezing, or a cool closet against an outside wall all work. The target is 40 to 50°F with moderate humidity. Avoid furnace rooms (too warm and dry) and refrigerators that also hold fruit, since ripening fruit gives off ethylene. Many gardeners store tubers in plastic bins with the lid cracked open, or in paper bags inside cardboard boxes.
| Storage medium | Best for | Watch for |
|---|---|---|
| Peat moss | Most homes | Too dry in heated spaces |
| Vermiculite | Damp basements | Mist lightly if tubers wrinkle |
| Wood shavings | Large collections | Keep shavings barely damp |
| Plastic wrap | Individual tubers | Rot if wrapped wet |
What do you do if tubers start to rot or shrivel?
Check monthly. Cut out soft or moldy spots with a clean knife, let the cut dry, and dust with sulfur or cinnamon. Shriveled tubers need a light mist on the packing medium. A tuber that is mushy all the way through should go in the trash, not the compost.
Dahlias are listed as toxic to dogs and cats by the ASPCA, usually causing mild stomach upset or skin irritation. Keep stored tubers out of reach of pets, and if a pet chews one, call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435. The same storage method also works for canna rhizomes and gladiolus corms.
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Zone and timing notes
Zones 3 to 6 should always dig. Zone 7 is borderline: tubers in sharp-draining soil under 4 to 6 inches of mulch often survive, but wet clay winters rot them, so dig your favorites. Zones 8 to 10 can leave dahlias in the ground with mulch, though digging and dividing every few years keeps clumps vigorous. No plant is truly deer-proof; deer browse dahlia foliage in many regions.
Bottom line
Wait one to two weeks after frost, dig gently with a fork, dry the clumps briefly, and store tubers at 40 to 50°F in barely damp peat or vermiculite. Check them monthly and you will have more plants to put back out after your last spring frost.
Related reading
- Divide perennials in early fall
- Digging spades and forks
- Potting benches and stations
- Forced amaryllis bulbs
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