Wait for a frost that blackens the foliage, then lift dahlias, cannas and gladiolus within about a week or two. NOAA’s 1991-2020 Climate Normals (32°F freeze probabilities) put the median first fall freeze at the Charleston airport station in late November, with early years bringing it in early November and late ones in mid-December. Along the coast you may not need to lift at all, because the average night in the coldest month stays above freezing. Farther inland and up toward the Upstate, the bulbs come out. Where you sit between those two places decides the job.
Do you have to dig them up in South Carolina?
The USDA Plant Hardiness Zone Map 2023 spans roughly 7a to 9b across the state, with Charleston at 9a. That zone system rests on a single number, the average annual extreme minimum temperature, so it says how low the worst night of a typical year gets, not how long the cold lasts or how wet the soil stays. The range is wide, and the decision follows it. Where the ground does not freeze deeply, dahlia tubers, canna rhizomes and gladiolus corms can stay put under mulch. Where it does freeze, they are safest lifted.
Charleston is the useful reference point. NOAA’s 1991-2020 Climate Normals show the mean daily minimum of its coldest month at 38.9°F. That is the mean daily minimum of the coldest month, so some January nights there still dip to freezing. On the peninsula and the milder coastal strip, leave them in the ground under a layer of mulch and lift only the ones you want to move or divide. The airport station sits inland of the peninsula and runs a little colder, so a garden right on the water is milder still.
The Upstate is a different story. Its seasons run several weeks tighter at both ends, with a first fall frost that comes earlier and a last spring frost that comes later. Nights in the heart of winter drop to freezing often enough that the soil gets cold through the top layer, and tubers sitting in it are at risk. Gardeners in that part of the state are safest lifting every fall. Anyone between the two, in the middle of the state, should treat the choice as a judgment call: check your own zone on the USDA map and the climate of your yard before deciding.
Cold is only half the picture on the coast. Winter rain in a heavy, slow-draining soil can rot a dahlia tuber faster than a cold night can, and dahlias are the riskiest of the three to leave in. A raised bed or a sloped spot with sandy, fast-draining soil gives them far better odds than low ground where water stands. Cannas are usually the most forgiving of the trio in the ground along the coast.
If you are unsure where your yard falls, the county extension office can tell you how cold your area gets and how local gardeners handle these bulbs. The Which Spring Bulbs Survive Your Winter guide covers the hardy bulbs that never need lifting at all, which makes a handy comparison. For bulbs beyond these three, see the Spring Bulbs section.
When to lift them
The signal is a frost that turns the foliage black and limp. Dahlias go first, since their leaves and stems collapse into dark mush after a freeze, while canna leaves turn brown and gladiolus leaves yellow and fall over. That frost kills the top growth, but the tubers underground are still alive and keep maturing. Lifting in the week or two after that frost gives the skins time to toughen and the tubers time to finish maturing.
Lift them in the week or two after the first frost blackens the foliage, which at the Charleston airport station means a window that typically opens in late November, a little earlier or later depending on the year. Peninsular Charleston is milder than the airport, so the frost there tends to come later, and some falls bring no freeze at all. In the Upstate the same job falls earlier than the Charleston dates, and the first hard frost comes sooner there. The full set of dates for your area is in First and Last Frost Dates in South Carolina.
Why not lift them earlier?
Digging while the foliage is still green looks like a safe way to beat the cold, but it produces tubers that are not ready for storage. Their skins are thin, they hold more water than they should, and they have not finished moving energy down from the plant. Tubers like that lose moisture through the skin and wrinkle, or stay damp and rot in the box. Rot in storage is a common reason a gardener opens a crate in February and finds mush where a full tuber used to be.
Waiting too long has its own cost. A hard freeze after the foliage has blackened can reach tubers that sit close to the surface, and a long wet spell keeps the soil cold and soggy around them. Aim for a dry day soon after the frost, when the soil is not saturated.
What if frost never comes?
Along the coast, some falls skip the freeze, and the foliage stays green into December. Do not lift on a calendar date in that case. If you plan to lift anyway, wait until the plants have clearly declined, with leaves yellowing and stems browning, and then cut them back and dig. If you plan to leave them in the ground, there is nothing to time: cut the dead stalks to a short stub, mulch, and keep the bed well drained.
When you do lift, work a garden fork in a wide circle around the clump, well outside the stalks, then pry up gently from below. A fork driven too close spears the tubers, and every cut is an entry point for rot. Tag each variety before the foliage disappears, because the colors and heights are hard to recall by spring.
Storing them over winter
The goal in storage is simple: keep the tubers from rotting and keep them from shriveling. Those two problems pull in opposite directions, which is why dahlias, cannas and gladiolus each want a slightly different setup. Cool, dark and slightly moist works for the first two. Gladiolus corms want the same cool and dark but drier.
How do you cure and clean them?
Curing comes first. After lifting, shake off the loose soil, leave the clumps in a shaded, airy spot out of the rain, and let the skins dry. Dahlias have hollow stems, so cut the stalks back to a short stub and let any water drain out before packing. Do not scrub with a brush or spray hard. A light shake and a wipe is enough, and in humid weather a longer drying period is better than a shorter one. Skins that feel dry and a little leathery are ready. A tuber that still feels cool and damp to the touch needs more time.
Do dahlias, cannas and gladiolus store the same way?
Not quite. Dahlia tubers are the most likely of the three to dry out into wrinkled husks, so pack them in a box or crate with a lightly damp medium such as peat moss, wood shavings or vermiculite. The medium should feel barely moist, never wet. Cannas can go in the same kind of packing and tolerate slightly more moisture, but a wet medium rots them quickly, so the same barely-damp rule applies. Large clumps can stay whole until spring, when you divide them.
Gladiolus corms are different. After lifting, cut off the stalk, let the corms cure dry in an airy place, then pull away the old shriveled corm at the base and set aside the tiny new cormels that cling to the sides. Store them in paper or a mesh bag, with no damp packing at all. Because South Carolina’s humid air keeps moisture around stored corms, the main risk for them is usually mold, so airflow matters more than moisture.
Pick a spot that stays cool and above freezing. An unheated basement or a closet on an outside wall suits most gardeners. A garage works along the coast, but in the Upstate a hard cold snap can freeze a garage, and frozen tubers turn to mush when they thaw. Avoid sealed plastic bags and any spot near a furnace or a window.
Regular checks save many tubers. Open the boxes and look at every clump about once a month, from the first month of storage until you replant. Pull out anything soft, slimy or moldy, cut off small damaged spots with a clean knife and let the cut dry. If tubers look wrinkled, mist the packing lightly. If you see condensation on the box or a musty smell, open it up and let it air out for a day.
What goes wrong
Common losses come down to four problems, and each one leaves a distinct sign.
- Rot shows up as soft, mushy tubers, often with a sour smell or white and gray mold. It comes from storing them damp, packing them before the skins dried, or letting them touch a diseased neighbor. Cure thoroughly, use only barely damp packing, and remove any infected piece right away before it spreads through the box.
- Shriveling looks like a raisin: wrinkled, light, hard tubers that feel hollow. Storage that is too dry or too warm causes it, and gladiolus corms and dahlia tubers are both vulnerable. A lightly damp medium and a cooler spot slow it, and a shriveled tuber that is still firm at the center can often be saved with a gentle misting.
- Lifting too early gives thin-skinned, watery tubers that rot or wrinkle within weeks. Wait for frost to blacken the foliage before you dig.
- Leaving them too far north for their hardiness zone means tubers that went into a freezing, wet winter and come out soft and brown in spring. This happens in the Upstate and anywhere the ground really freezes.
The mistake near the coast is the reverse: lifting every year when the mild soil would have kept the plants fine. If you are unsure, lift a few of your best dahlias and leave the rest under mulch for a winter, then compare what comes up in spring. While you are sorting bulbs, fall is also the time to plant hardy bulbs, and Planting Spring Bulbs in South Carolina covers what goes in now. For other seasonal jobs across the state, the South Carolina guides collect them in one place.
Common questions
Can I leave dahlias in the ground near Charleston?
Often, yes. The coldest month there has a mean daily minimum of 38.9°F, according to NOAA’s 1991-2020 Climate Normals, so deep ground freezes are not the main threat. Drainage matters more. In well-drained soil with mulch, tubers usually come through. In heavy clay that stays wet all winter, lift them or move them to a raised bed.
Do I have to wait for frost before digging?
Waiting for the foliage to be blackened by frost gives the tubers time to mature. Where frost comes late or not at all, wait until the leaves have clearly died back before cutting them down and lifting, rather than digging on a set date.
Do cannas and gladiolus need lifting in the Upstate?
Generally yes: lifting is the safer choice for all three there. The first fall frost comes earlier in the Upstate than at the Charleston airport station, winters are colder, and the ground can freeze enough to damage rhizomes and corms. Lift after the frost blackens the foliage and store them the way you would dahlias, with gladiolus kept drier.
What should I do with potted dahlias and cannas?
Potted plants can skip the digging. After frost blackens the foliage, cut the stalks back, stop watering and move the pot into a cool, dark spot that stays above freezing, such as a basement or an unheated closet. Give the soil a light sprinkle once a month so it does not dry to dust, and bring the pot back into the light after the last spring frost has passed.
Sources : ncei.noaa.gov