In Indianapolis, dig dahlias, cannas and gladiolus after the first hard frost blackens the foliage. By NOAA’s 1991-2020 normals, that frost arrives between October 21 and October 30, so lifting falls from roughly the last week of October into the first half of November. Northern Indiana runs earlier, the south later. Yes, you have to lift them across most of the state. Here is why, and how to do it so the tubers are still firm in March.
Do you have to dig them up in Indiana?
Yes. Plan to lift all three from late October through mid-November, once frost has blackened the tops. Indiana’s ground freezes, and these plants are tropical or subtropical in origin. Dahlia tubers, canna rhizomes and gladiolus corms are all storage organs full of water, and water that freezes inside them ruptures the tissue. What looks like a firm tuber in November turns to mush by April.
What the numbers say
The USDA Plant Hardiness Zone Map 2023 puts Indiana in zones 5b to 7a. That system rests on a single variable, the average annual extreme minimum temperature, so it is a blunt instrument for a decision about tender tubers. A second figure is more useful. NOAA’s 1991-2020 Climate Normals for Indianapolis, the reference station here, give a mean daily minimum of 20.9°F in the coldest month. That is 11 degrees under freezing as an average night, before any cold snap pushes lower.
Mulch cannot fix that. Straw or shredded leaves slow the rate at which cold moves down, but they do not warm soil that sits under a cold-air mass for weeks. Because Indianapolis is only one point on a map that runs from the Chicago-influenced north to the Ohio River in the south, conditions in your yard will differ. The reference city tells you the central tendency, not your own microclimate.
Where the line falls, and where it blurs
In the colder northern counties, the answer is simple: everything comes up, every year. In the mildest southern pockets, a canna clump under a thick mulch will sometimes make it through a gentle winter. That is a gamble, not a plan, and the loss comes in the winter you stop expecting it. A hard January can kill a clump that survived five easy ones, and you will not know until June, when nothing sprouts. Dahlias are the least forgiving of the three. If you have a named, hard-to-replace variety, lift it no matter where in the state you garden.
Hardy spring bulbs run the opposite way. Tulips and daffodils need the cold and stay put, which is covered in Which Spring Bulbs Survive Your Winter and the wider Spring Bulbs section. Summer-flowering tender bulbs are the ones with an expiration date on their stay in the ground.
When to lift them
The signal is a frost that turns the foliage black and limp. Dahlia leaves go from glossy green to something resembling wet charcoal overnight. Cannas collapse. That frost does not hurt the tubers, which sit insulated under the soil, and it tells the plant to stop growing and send its last energy downward.
At Indianapolis, NOAA’s normals put the 30 to 70 percent probability band for a 32°F freeze between October 21 and October 30. Lift within a week or two of that blackening frost, which works out to roughly October 28 through mid-November. You can find your own county’s numbers in First and Last Frost Dates in Indiana. The direction matters. Northern Indiana gets its first frost earlier, so lifting moves earlier there. Southern Indiana can run a fortnight or more later in autumn, and a gardener near the Ohio River may still be cutting dahlias in early November while a South Bend gardener has already lifted.
Why waiting for the frost matters
Tubers dug in September, while the plant is still green, are immature. The skin is thin, the tissue is full of sap and the eyes at the crown, where next year’s shoots form, have not fully set. Put that tuber in storage and it respires, sweats and rots from the cut ends inward. The tops do the final work of curing the root system, and cutting that short costs you more than the extra month of waiting.
The wait has a limit. Leaving dahlias in the ground weeks after the frost, through repeated hard freezes, lets the cold reach the tubers directly. A week or two after the blackening frost is the sweet spot. If a prolonged cold snap is forecast right after the first frost, lift sooner.
Gladiolus follow a slightly different cue. Many gardeners lift the corms when the leaves yellow and brown, which can happen before a hard frost, because the corms are done building by then. Cannas can wait until frost blackens them, but do not let the rhizomes sit in saturated cold soil.
Pick a dry day. Dig with a fork, starting a foot or so out from the stem, so you lift rather than stab. Dahlia necks snap easily, and a broken neck means a tuber that will not sprout.
Storing them over winter
All three need the same three steps in the same order: cure, clean lightly, store. Curing means letting the surface dry in a sheltered, airy spot out of direct sun and away from rain. A garage bench or covered porch works. The skin firms up and small nicks seal over. Clean means knocking off the loose soil with your hands. Skip the hose. Washing is where many gardeners start a rot problem, because water sits in the crown and the divisions.
The storage spot has to be cool, dark and above freezing. In an Indiana winter, with a mean coldest-month minimum of 20.9°F at Indianapolis, an unheated detached garage can drop below 32°F on the worst nights and kill everything stored there. A basement, an insulated crawlspace or an interior closet is safer. The target is a place that stays cool without freezing, with some air movement.
The plants differ in what they want around them:
| Plant | Storage medium | Moisture | Main risk |
|---|---|---|---|
| Dahlia tubers | Lightly packed in barely damp peat, vermiculite or wood shavings, in a ventilated crate | Slightly moist | Shriveling if too dry, rot at the neck if too wet |
| Canna rhizomes | Loosely packed in slightly damp material, or in a box with some soil still clinging | Slightly moist | Drying out to a hard shell, or mold |
| Gladiolus corms | Dry, in mesh bags or paper in a single layer | Dry, with good airflow | Rot if any moisture lingers |
Gladiolus are the odd ones out. Once the corms are cured, the old shriveled corm at the base and the husk can be pulled away, and the small cormels can be kept separate if you want to grow more. Corms store like onions, so keep them dry. Dahlias and cannas, on the other hand, need that whisper of humidity because their tubers are fleshy and dehydrate.
Check the whole stash once a month, from December through March. It takes ten minutes. Pick a few tubers from each container, squeeze gently and look for the things covered next. Remove anything soft or moldy before it spreads, and if the rest look wrinkled, lightly mist the packing material. This monthly look saves more tubers than any storage trick, because every problem is cheap to fix when found early.
If you also tuck spring-flowering bulbs into the ground in fall, Planting Spring Bulbs in Indiana covers that side of the calendar, and it runs on a different clock from the one you are keeping for summer tubers.
What goes wrong
Rot is the biggest killer. It shows up as soft, brown or black patches, often at the neck of a dahlia or the cut end of a canna, with a sour smell and sometimes fuzzy gray or white mold. Too much moisture in storage, tubers packed while still wet or lifting before the tops matured all cause it. Cut away small spots with a clean knife, let the cut surface dry, and dust with sulfur if you have it. A tuber that is soft all the way through is finished. Throw out anything mushy right away.
Shriveling is the opposite problem. A dahlia tuber turns wrinkled and rubbery, like a raisin, and cannot push out a shoot if it loses too much water. Cannas dry into a hard shell. The fix is a hint more humidity: a little dampness in the packing material, a loosely closed container rather than an open one. Catch it in January and the tuber usually recovers. By March it may not.
Lifting too early gives you the rot just described, plus tubers with soft skin that never harden properly. If a surprise early frost forces your hand before the tops have fully died, let the lifted clumps sit a little longer in the curing spot before packing them away.
The last mistake is geographic. A tip from a friend two hours south, or a canna that overwintered once in a mild year, can mislead a gardener farther north. Indiana’s hardiness range runs from 5b to 7a in the USDA system, and the north is meaningfully colder than Indianapolis. If you are north of the reference city, assume lifting is non-negotiable, and lift on the early side of the window.
Common questions
Can I leave dahlias in the ground in southern Indiana?
You can try, and some gardeners get away with it in mild winters, but no source in the data here supports it as reliable. The coldest-month mean minimum is 20.9°F even at Indianapolis, and the south is only a bit milder. Lift anything you would be sorry to lose, and treat a leave-in-ground clump as a bonus experiment.
What if a hard freeze hits before I get to them?
A freeze that blackens the foliage is the normal signal, not an emergency. The tubers are insulated by soil. Cut the stalks back, wait a few days for a dry spell, and lift within a week or two. If the ground freezes solid before you lift, wait for it to thaw enough to dig without tearing the roots.
Do I have to wait for frost to lift gladiolus?
No. Gladiolus corms are commonly lifted once the leaves turn yellow and brown, which can come before a killing frost. Dahlias and cannas are the ones that benefit most from waiting for the blackening frost.
When do they go back out in spring?
After the last spring frost date for your area. Even then, Purdue notes that roughly a 10 percent chance of a 32°F event remains after the published spring date, so keep a sheet or bucket ready if you plant on the early edge. Start dahlias and cannas indoors in pots earlier if you like, but harden them off before they go in the ground. More local guidance lives in the Indiana guides.