In Tennessee, wait for the first frost that blackens the foliage of your dahlias, cannas and gladiolus, then lift them within about a week or two. At Nashville’s frost normals, that puts the job in November, and earlier on the Cumberland Plateau and in the cooler parts of East Tennessee. Only the mildest lowland beds can leave them in the ground under mulch. Skip the calendar and watch the leaves, because the plants announce when they are finished.
Do you have to dig them up in Tennessee?
The USDA Plant Hardiness Zone Map 2023 puts Tennessee anywhere from zone 5b to zone 8a. That system rests on a single number, the average annual extreme minimum temperature, so it tells you how bad the worst night gets, not how long the cold lingers. For a plant that stores energy in a fleshy root, the lingering is what counts.
What the Nashville numbers say
Nashville is the one place with a clean reading. NOAA’s 1991-2020 Climate Normals put the mean daily minimum of its coldest month at 30.1°F. An average January night there lands barely under freezing, which sounds forgiving until you remember that an average hides the cold snaps on either side of it. Soil in the lowlands usually freezes shallowly and thaws again, and a dahlia tuber, canna rhizome or gladiolus corm sitting a few inches down can sometimes ride that out. Sometimes is the operative word.
Where the line falls
The honest line runs between the warm lowlands and everything cooler. In the mildest, best-drained, most sheltered beds of the warm end of the state, cannas can stay put under a thick blanket of mulch, and a gardener willing to lose a few plants can try the same with dahlias. Gladiolus corms are the least dependable of the three left in the ground. Across the Cumberland Plateau and the higher ground of East Tennessee, which run cooler than Nashville, the ground freezes harder and longer, and all three have to come up. The zone 5b end of the range is nowhere near a gamble.
Winter wet matters as much as winter cold. Tennessee’s heavier clay soils hold water through a mild, rainy January, and a tuber that sits in cold, saturated ground rots whether or not it freezes. A bed that drains poorly changes the verdict even in a warm spot. For how other bulbs handle the same winters, see Which Spring Bulbs Survive Your Winter.
The rule most Tennessee gardeners can write down is this: lift all three wherever the ground freezes deeply, and mulch in place only in the mildest, well-drained lowland beds. When in doubt, dig. Lifting costs an afternoon, and a frozen tuber is gone for good.
When to lift them
The signal is a frost hard enough to blacken the foliage. A light touch of frost that nips a few leaf edges is not it. You want the whole top of the plant limp, dark and collapsed, the way a basil plant looks after the first real freeze.
The window, set by the first frost
NOAA’s 1991-2020 Climate Normals for the Nashville station give the first fall freeze, meaning 32°F, a probability of 30 to 70 percent between October 28 and November 8. Treat that as the stretch in which the frost that ends the season usually arrives. Lift one to two weeks after the first blackening frost, which at Nashville falls between October 28 and November 8, so the digging lands in November. Colder places get their first frost sooner. On the Cumberland Plateau and at elevation in East Tennessee, expect that frost before the Nashville range and move your lifting earlier by the same margin. The Nashville window is a reference point, not a statewide calendar, so your own garden’s first blackened leaf is the better clock. If you want the local dates for your county, see First and Last Frost Dates in Tennessee.
Why waiting beats rushing
The pause after frost is not laziness. Until the foliage dies back, the plant is still moving sugars down into its storage organs, and the skin of a dahlia tuber or a canna rhizome is still thin. Dig a tuber in September because the bed looks tired and you get a soft, waterlogged, underfed lump. Soft tissue breaks, and broken tissue invites rot in storage by February. The extra week or two lets the skin toughen and the energy settle in.
Dahlias have a second reason to wait. Their stems are hollow, and cutting them while the plant is still green leaves an open pipe straight to the crown, where water and fungi can follow. A frost-killed stem has already begun to seal itself.
The wait has a limit, though. If the forecast shows a hard, sustained freeze after the first frost, do not leave the roots to see what happens. A frost that only blackens leaves is not a threat to the roots under mulch or soil, but a freeze that lasts through several nights is. Dig when the weather turns, not when the calendar permits.
A practical sequence works well. Cut the stalks back to a short stub, loosen the soil around the clump with a garden fork set well out from the plant (a spade slices through tubers far too easily), and lift from the side. Shake off the loose dirt and stop there. Do not wash yet.
Storing them over winter
Storage comes down to a short list: cure them, clean them lightly, then keep them cool, dark and just moist enough that they neither rot nor shrivel. The three plants want slightly different treatment, and treating them the same is where most losses start.
Curing and cleaning
Curing means letting the surface dry in a sheltered, airy spot out of the sun and out of the rain, such as a garage, a porch or a covered shed. Dahlia tubers and canna rhizomes need the skin dry to the touch and no more. Gladiolus corms need a thorough cure, until the husks feel papery and the old, spent corm underneath the new one snaps off easily. Clean lightly by brushing off dry soil. Soaking and scrubbing leaves wet crevices, and wet crevices are where rot starts. Remove any piece that is already soft or mushy and dust cut surfaces if you wish.
How the three differ
| Plant | What you store | Moisture | Packing |
|---|---|---|---|
| Dahlia | Tuber clump with a short stem stub | Slightly moist | Boxes or crates with a barely damp material such as peat, vermiculite or wood shavings |
| Canna | Thick rhizome clumps | Slightly moist, forgiving | Similar to dahlias, or wrapped loosely in newspaper inside a crate |
| Gladiolus | Corms, with the old spent corm removed | Dry and airy | Mesh bags, paper bags or open trays, never sealed in plastic |
Dahlia tubers are the fussiest. They shrivel quickly in dry air and sulk in wet packing, so they want a medium that is damp only in the way a wrung-out sponge is damp. Cannas are easier on you, since the big rhizomes carry plenty of water and tolerate a bit of neglect. Glads sit at the other end. A gladiolus corm is a dry, papery little onion of a thing, and it keeps best when stored the way you would store a shallot.
The place matters as much as the packing. Look for a spot that stays cool, dark and above freezing, and that does not swing from warm to cold. A basement corner, an unheated but insulated room or a closed cabinet against an interior wall all work in Tennessee. An attached garage works if the coldest nights never reach it. A spot beside a furnace or water heater dries everything out.
Then comes the step that saves more tubers than any other: check them once a month. Open the boxes and look. Pull out anything soft, moldy or smelly, and if the rest feel light and wrinkled, mist the packing lightly. If the packing looks wet, open the lid for a day. A monthly look costs about ten minutes, and it is the difference between a box of healthy tubers in April and a box of compost. When spring comes, the tulips and daffodils that never left the ground will be up well before you replant these, and Spring Bulbs covers that side of the garden.
What goes wrong
Almost every failure in storage and in the ground traces back to one of four causes. Each leaves recognizable signs.
Rot
Rot is the most common loss. You find a tuber that is soft, discolored, sometimes slimy, often with a sour smell, and the rot spreads to neighbors in the same box. It comes from packing too wet, storing before the surface dried, lifting wet and sealing the clump in plastic, or lifting too early when tissue was still immature. Prevent it by curing first, packing barely damp, using breathable containers and cutting out soft spots at once. A single bad tuber left alone can ruin a crate.
Shriveling
Shriveling is rot’s opposite, and it looks like a raisin. Tubers turn wrinkled, light and hard, and may never wake in spring. It happens in a dry, warm room or with too little packing material. If you catch it in time, a light misting of the packing and a move to a cooler place can revive a tuber that is only starting to wrinkle. Gladiolus corms are the exception, because they are meant to stay dry.
Lifting too early, or leaving them in too far north
Lifting too early gives you immature, thin-skinned tubers that rot in storage, which is why the rule is to wait for the blackening frost, then dig within one to two weeks. The mistake in the other direction is leaving tubers in the ground where winters run too cold. The mild-winter advice that works near Nashville does not transfer to the Cumberland Plateau or the colder parts of East Tennessee, and a clump left in frozen ground turns up in spring as mush. If your garden sits on a hilltop, a north slope or a frost pocket, treat it as colder than the nearest town.
Common questions
Can I leave cannas in the ground in Tennessee?
In the mildest lowland beds with good drainage and a heavy mulch, many gardeners do, and cannas are the best of the three for the experiment. Nashville’s coldest-month mean minimum of 30.1°F (NOAA, 1991-2020) suggests a shallow, brief freeze there. On the Plateau and in higher East Tennessee, dig them. If the bed stays wet in winter, dig them anywhere.
Do I have to wait for frost, or can I dig when the plants look tired?
Wait for the frost that blackens the foliage, then lift within about a week or two. Early digging produces immature tubers that tend to rot in storage. If a hard, sustained freeze is forecast, do not wait out the full stretch, because the roots matter more than the leaves.
My dahlias were killed by an early frost. Is it too late?
No, that is the signal you were waiting for. Cut the stalks back to a short stub, give the clumps a week or two, and then lift on a dry day. Colder parts of Tennessee get this frost sooner than Nashville’s October 28 to November 8 range, so the timing moves earlier there.
When do the stored tubers go back out?
After the last spring frost has passed and the soil has warmed. Cooler parts of the state get that last frost later, so replant later there. For help with spring planting across Tennessee, see Planting Spring Bulbs in Tennessee, and for more regional gardening, browse the Tennessee guides.