In most of Illinois, dahlias, cannas and gladiolus have to come out of the ground every fall. Wait for the first frost that blackens the foliage, then lift them about a week or two later, which lands in early to mid November around Chicago. Dry them briefly, pack them cool and dark, and check them monthly. The reasons behind each step decide whether you get tubers in April or a bag of mush.
Do you have to dig them up in Illinois?
Yes, for nearly every Illinois garden. The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) places Illinois in zones 5a to 7b, a wide spread, but the rule that matters is simple: where the ground does not freeze deeply, these plants can stay put under mulch, and where it does, they must come up. Most of the state falls in the second group. Plan to lift dahlia tubers, canna rhizomes and gladiolus corms every fall, once frost has killed the tops.
Chicago shows why. NOAA’s 1991-2020 Climate Normals put the mean daily minimum of the coldest month at 18.8°F at the Chicago reference station. That is a monthly average, not a record low, so many individual nights run colder, and a month of lows that far under freezing is enough to freeze the soil where these storage organs sit. Dahlia tubers and canna rhizomes are fleshy and full of water. Once frozen, they thaw into brown, odorless slush that never sprouts.
Where the line falls
The USDA system rests on a single variable, the average annual extreme minimum temperature, so it says nothing about how wet or heavy your soil is. Within Illinois, the north sits at the 5a end and the far southern tip reaches 7b. Gardeners at the southern end have a better argument for leaving things in the ground, with a thick layer of mulch and well-drained soil. Even there, a stretch of hard cold can still reach the tubers, so treat it as an experiment: leave a few and lift the rest. A mild winter can fool you, and one cold snap undoes it.
Gladiolus is the one most often left in by mistake. Gardeners see it described as a bulb and assume it behaves like a tulip. A gladiolus corm is a tender summer-flowering plant, and the cold tolerance that lets daffodils sit through a Chicago January does not apply to it. The hardy group is covered in Spring Bulbs, and Which Spring Bulbs Survive Your Winter sorts out which ones need no lifting at all. The three plants here belong on the other side of that line.
Gardens differ from the airport station, too. The Chicago figures come from a weather station at the airport, and suburban and rural gardens often see their first fall frost one to two weeks earlier. A low-lying yard in the collar counties or a farm field in the north of the state may get its killing frost well before the reference dates. Check your own county’s normals before you commit to a date.
When to lift them
The signal is a frost that blackens the foliage. Dahlia leaves turn dark and limp, canna leaves collapse into a gray-green slump, and gladiolus leaves yellow and brown. That frost does not hurt what is underground. It tells the plant to stop growing and send its reserves down into the tubers, rhizomes and corms.
NOAA’s 1991-2020 Climate Normals for the Chicago reference station put the first fall 32°F freeze between October 24 and November 3, based on the 30 to 70 percent probability band. Your lifting window follows that frost by about a week or two. Counted from the frost range, that puts lifting in early to mid November around Chicago, and a little earlier in the northern part of the state, where fall comes first. Lift roughly one to two weeks after the first killing frost, which means early to mid November at the Chicago reference figures.
Some gardeners are tempted to lift in September or early October, before the first frost, to beat the weather. Skip it. A plant still in active growth has tubers with thin skins and soft tissue. They bruise easily and lose moisture quickly, and once stored they either shrivel or rot from the cut stem end. The extra week or two in the ground lets the skins toughen and the energy settle, so the stored pieces last until spring.
The waiting has limits. You do not want to leave tubers in soil that is wet and cold for a long stretch, or in ground that is starting to freeze hard. If a frost is forecast to be very severe soon after the first one, lift sooner. A warm, dry day is best, because soil falls off more easily and the pieces go in storage drier.
How to do it
Cut stems down to a few inches. For dahlias, push a garden fork in a foot or so out from the stalk and lever the clump up gently. The necks break easily, and a snapped neck rarely grows. Cannas are tougher: fork up the whole mass of rhizomes and shake off loose soil. Gladiolus corms lift from the soil with a trowel or fork once the leaves have died back, and the old corm underneath can be broken off later.
If you are unsure about timing in your own yard, the First and Last Frost Dates in Illinois page lists dates by area so you can adjust from the Chicago figure. Cold pockets and city-warmed lots can differ by more than a week.
Storing them over winter
The goal is storage that is cool, dark and slightly moist, so the tubers neither rot nor shrivel. The steps are the same for all three: cure, clean lightly, pack, and check. What changes from plant to plant is how much moisture each one wants.
Start with curing. Let freshly lifted pieces sit somewhere sheltered, such as a garage or porch, until the surface feels dry. Do not wash dahlias or cannas hard with a hose; brush off loose soil and leave the rest. Washing pushes water into cuts and nicks, which is where rot begins. Gladiolus needs the longest cure and the driest conditions, and it is finished when the husks feel papery and the small new corms separate from the old.
| Plant | What you are storing | Packing | Moisture | Main risk |
|---|---|---|---|---|
| Dahlia | Tuber clump with neck | Loose in a box or crate with a dry or barely damp material such as peat, shavings or vermiculite | Slightly moist; never wet | Rot at the neck, or shriveling |
| Canna | Rhizome clump | Same approach as dahlias, in a box or paper-lined crate | Slightly moist; dries out faster than you would expect | Shriveling, then rot if it gets damp |
| Gladiolus | Corms, old corm removed | Paper or mesh bags, or a shallow tray, in a single layer if you can | Dry and airy | Mold from trapped moisture; hidden insects |
Dahlias are the fussiest of the three. Pack them so the pieces do not touch, leave the neck exposed to air, and keep the medium just barely damp. Cannas tolerate a bit more handling, though their rhizomes dry out in a heated basement within weeks. Gladiolus corms are the opposite. Moisture trapped around them invites mold, so use paper or mesh and good air. Check corms for silvery streaks or scarring, which can mean thrips, and discard any that look suspect.
The place matters as much as the packing. A cool, dark spot that stays above freezing suits all three: an unheated basement, a cellar room, or an insulated garage that does not go below freezing. A heated, bright, dry room will shrivel them, and a cold one will turn them to mush. Avoid places where temperature swings a lot, like a garage wall that gets sun in the afternoon.
Check your stored pieces once a month through the winter. Look for soft spots, mold or wrinkling. Cut off any rotting section down to firm, clean tissue and let the cut dry before returning it to storage. If everything looks plump and a little firm, leave it alone. If the skins are wrinkled, mist the packing lightly. If anything smells sour or feels slimy, take it out before it spreads to its neighbors. That monthly look is the step that saves them.
What goes wrong
Most failures come from four mistakes, and each one leaves a clear sign. Knowing the sign tells you what to fix before the plant is lost.
Rot
Rotted tubers feel soft or mushy, sometimes with fuzzy mold or a sour smell. The causes are excess moisture, too little air, or storing pieces before they had cured. Prevent it with a dry cure, loose packing and a cool, ventilated spot. Cut away small soft areas to clean tissue and dry the cut before replacing the piece.
Shriveling
Shriveled pieces look wrinkled and leathery, with a hollow feel. The packing was too dry, the room too warm, or the tubers were lifted before their skins hardened. Light misting of the packing helps if you catch it early, and a cooler spot slows further loss. Badly shriveled pieces with no firm tissue left rarely recover.
Lifting too early or too late
Pieces lifted before frost have thin skins, and many shrivel or rot by midwinter. Lifting too late, after soil has frozen hard, risks damaged tubers and broken necks. The window is the one or two weeks after the blackening frost.
Leaving them in one zone too far north
Gardeners in the north of the state sometimes copy advice written for milder places and mulch their dahlias in the ground. The Chicago reference station averages 18.8°F for its coldest month’s lows, and farther north runs colder, so a layer of mulch cannot hold the cold back from the roots. In spring the clump shows up as a brown, collapsed lump. Treat any Illinois garden as a lift-and-store garden unless it sits at the far southern end of the state, and even there, keep a few pieces indoors as insurance. For more local planting advice, see the Illinois guides.
Common questions
Can I leave dahlias in the ground in Illinois if I mulch heavily?
In most of the state, no. Chicago’s coldest month averages lows of 18.8°F, according to NOAA’s 1991-2020 normals, and the soil freezes deep enough to damage fleshy tubers. Mulch slows the freeze but does not stop it. Only the far southern end of the state, near the 7b end of the USDA range, offers a realistic chance, and even there a few spare tubers kept indoors are wise.
What if frost has not come by mid-November?
Wait for it, but not forever. The Chicago reference station’s first 32°F freeze falls between October 24 and November 3 in the 30 to 70 percent probability band, so a late frost is unusual but not rare. If the ground is cold and wet and no frost has come, you can cut the plants down and lift them anyway, since the tubers will have matured. Do not leave them in ground that is starting to freeze hard.
Do gladiolus corms need lifting every year?
In Illinois, yes. They are tender and will not come through a typical winter in the ground. Lift them after the foliage browns, cure them in a dry airy spot, remove the old shriveled corm, and store them in paper or mesh. While the fork is out, fall is also the time to plant hardy tulips and daffodils, covered in Planting Spring Bulbs in Illinois.
When do I plant them back out?
After the last spring frost has passed and the soil has begun to warm. Tender tubers planted into cold, wet ground tend to rot before they grow. Suburban and rural gardens usually see the last spring frost later than the airport reference, often by one to two weeks, and the colder north is later still, so check your own county. Starting dahlias and cannas in pots indoors a few weeks ahead gives them a head start without risking them to a cold snap.