Dig dahlias, cannas and gladiolus after the first frost blackens the foliage, within a week or two of it. Around Milwaukee, NOAA’s 1991-2020 normals put the first fall freeze between October 17 and October 29, so that is when the fork comes out. Inland and farther north, the calendar moves earlier. All three have to come up, because Wisconsin ground freezes. After that, curing, storage and regular checks decide whether the tubers last until May.
Do you have to dig them up in Wisconsin?
Yes, everywhere in the state. Lift dahlias, cannas and gladiolus every fall, from Milwaukee to the northern counties, because none of the three survives a frozen root zone. Where the ground never freezes deeply, these plants can sit out winter under a layer of mulch. Wisconsin is not that place.
What the zone and the winter numbers say
The USDA Plant Hardiness Zone Map 2023 places Wisconsin between zone 3b and zone 6a. That system rests on one variable, the average annual extreme minimum temperature. It describes the coldest night of a typical winter and says nothing about how long the cold lasts or how wet the soil stays. For that, look at the NOAA NCEI Climate Normals for 1991-2020. At the Milwaukee station, the mean daily minimum of the coldest month is 17.2°F. That is not a record low. It is the average night in the worst month.
Milwaukee also sits toward the milder side of the state, with Lake Michigan taking some of the edge off. Move inland or north and winters get harsher, so the verdict only firms up. Other parts of Wisconsin differ from the Milwaukee figures, and they differ in the direction that makes digging more necessary.
What freezing does to a tuber
A dahlia tuber is a bit like a sweet potato, a fat storage organ packed with water. Canna rhizomes and gladiolus corms are built on the same plan. Freeze one and ice crystals rupture the cells. Thaw it in April and what you find is gray mush with a sour smell.
A few clumps do come through mild winters in sheltered corners, and gardeners retell those stories for years. They are luck, though, and nobody can predict which winter or which spot in the yard will allow it. A clump you paid for or spent a summer admiring should not depend on that.
Hardy bulbs like tulips and daffodils can stay in the ground all winter, and Which Spring Bulbs Survive Your Winter sorts out which ones. Dahlias, cannas and gladiolus belong to the tender summer group, which is why they run on their own calendar rather than the one for Spring Bulbs.
When to lift them
Wait for the frost that blackens the foliage. That is the signal for all three. Dahlia leaves turn dark and limp, canna leaves go translucent and slimy, and gladiolus foliage collapses if it has not already yellowed. The tubers underneath are fine at that point, and the plant has finished sending energy down to them. Lift within a week or two after that first blackening frost, not much sooner and not much later.
For the calendar, NOAA’s 1991-2020 Climate Normals for the Milwaukee station put the first fall freeze (32°F) between October 17 and October 29. That range is NOAA’s 30-70% probability band, the stretch in which a freeze goes from fairly possible to more likely than not. In the Milwaukee area, then, lifting starts once a frost lands somewhere in that stretch and wraps up within a week or two after it. A warm fall pushes the work later, and an early freeze pulls it earlier.
Lakeshore, inland and north
Milwaukee is one reference point, not the whole state. Lake Michigan delays the first fall freeze along the lakeshore, so gardeners right on the water often get extra weeks of bloom. Inland southern Wisconsin typically freezes in early October, and the north freezes far earlier. Colder places get an earlier first frost, so lifting there moves earlier as well, never later.
A gardener in the northern counties may be digging tubers while a lakeshore neighbor still cuts dahlia bouquets. Look up your own dates in First and Last Frost Dates in Wisconsin, then watch the thermometer and the plants rather than the calendar.
Why lifting early gives tubers that rot
Digging on a pleasant weekend while the plants are still green is tempting. Resist it. Until frost shuts the plant down, the foliage keeps feeding the underground parts, and the skins thicken and the tissue firms up as that happens. Tubers pulled from a green plant have thin skins and a lot of water in them. Dahlia crowns, where next year’s buds form, may not be fully set.
In storage those tubers lose moisture unevenly, bruise at the slightest handling and tend to rot from the stem end. Waiting for the frost is free insurance.
Waiting too long has its own cost. Cold, wet soil after a frost sits against the tubers, and a hard freeze that penetrates the ground can reach them. Pick a dry day, loosen the soil with a garden fork well away from the stems, lift the clump gently, and cut the stalks back to short stubs. Do not pry on the stalk, since dahlia necks snap easily.
Once the bed is empty, it can take tulips and daffodils. Planting Spring Bulbs in Wisconsin covers the timing for those.
Storing them over winter
The routine has three steps: cure, clean lightly, then store cool, dark and slightly moist. The goal is to avoid two opposite failures. Too wet and tubers rot, and too dry and they shrivel into wrinkled husks. The safe middle is narrow, which is why checking on them during winter matters more than any special material.
Curing and cleaning
Spread the clumps in a sheltered, airy spot out of rain and direct sun, such as a porch, a garage floor or a spare room, until the skin feels dry and loose soil crumbles away. Dahlias and cannas need a modest curing time. Gladiolus corms need longer, in a warm, airy place, until the husks turn papery and the old shriveled corm at the base pulls away easily.
Clean lightly. Shake or brush off the soil and skip the hose or pressure washer. A damp tuber going into a box in November is a rotten tuber by February. Leave a short stub of stem on dahlias, and do not snap the neck, because the buds sit right there.
Where and how for each plant
Pick a spot that stays cool, dark and above freezing. An unheated basement away from the furnace works well for most Wisconsin homes. Detached garages and sheds are riskier. NOAA’s normals show a mean daily minimum of 17.2°F in the coldest month at the Milwaukee station, and an uninsulated outbuilding will follow the outdoor temperature down on the cold nights.
The three plants do not want quite the same conditions:
| Plant | What you store | Packing | Moisture |
|---|---|---|---|
| Dahlias | Tuber clumps with the crown | Vented boxes or crates, packed in barely damp wood shavings, peat or a similar medium | Slightly moist. Thin skins shrivel fast if the air is dry. |
| Cannas | Fleshy rhizome clumps | Boxes or paper-lined crates with barely damp packing | Slightly moist, a little more forgiving than dahlias |
| Gladiolus | Cured, cleaned corms | Paper or mesh bags, or open trays | Dry and airy. Damp packing invites mold and rot. |
Gladiolus is the outlier. Dahlias and cannas are storage organs that must not dry out, while gladiolus corms are dormant bulbs that do best left alone in dry air.
Whatever the plant, open every box and check it once a month all winter. That habit is what saves the clumps. A soft spot caught early can be cut away and left to dry. If you wait until spring, the whole clump is usually gone. Wrinkled dahlia tubers get a light mist on the packing material, and fuzzy mold calls for more ventilation and a closer look at how damp the packing is.
What goes wrong
Rot and shriveling
Rot looks like soft, dark patches, a sour or musty smell and sometimes gray fuzz. It comes from tubers packed too wet, boxes with no air movement, or tubers lifted before they matured. Prevention is the routine above: cure properly, pack barely damp rather than wet, ventilate, and cut away any soft spot as soon as you find it.
Shriveling is the mirror image. Tubers turn wrinkled, leathery or hollow-feeling because the room is too warm or too dry. A light mist on the packing, or a move to a cooler spot, usually stops it if you catch it early. Badly shriveled tubers rarely recover.
Timing mistakes
Lifting too early shows up as mushy, thin-skinned tubers by midwinter. The cure is patience: wait for the blackening frost. Leaving clumps in the ground is the other mistake, usually because the advice came from a gardener in a milder climate. In Wisconsin, with USDA zones running from 3b to 6a, that advice does not hold. The result is a bed in spring where nothing comes up and the digging turns up gray mush.
If a clump matters to you, lift it. That is the safer default anywhere in the state, even at the lakeshore, where the first freeze comes last.
Common questions
Can I leave dahlias in the ground in Wisconsin if I mulch heavily?
Not reliably. Mulch slows how fast ground freezes, but Wisconsin winters are long and cold enough to get through it. At the Milwaukee station, the coldest month has a mean daily minimum of 17.2°F (NOAA NCEI 1991-2020), and that is one of the milder spots in the state. Treat any clump left outside as a gamble you will probably lose.
What if frost arrives before I am ready to dig?
Nothing is lost yet. A frost that blackens the foliage kills the tops but leaves the tubers underground intact. Cut the stalks back and lift within a week or two. Waiting much longer lets cold, wet soil sit against the tubers and raises the risk of a hard freeze reaching them.
Do gladiolus come up at the same time as dahlias?
Usually close to it, though gladiolus is less fussy. Leaves often yellow around the same stretch, and the corms are lifted once the foliage has died back. They then need a longer cure than dahlias and cannas and go into dry storage rather than damp packing.
Where in my house should I store them?
An unheated basement away from the furnace suits most homes, as long as it stays cool, dark and above freezing. Avoid unheated garages and sheds, which follow outdoor temperatures down on the coldest nights. For more fall timing by region, the Wisconsin guides cover the rest of the calendar. Whichever spot you pick, one detail matters most: put a box where you will walk past it, since a box you see monthly is a box you will actually check.