In Maine, all three come out of the ground every fall. Lift dahlias, cannas and gladiolus after a frost blackens the foliage, which at Portland falls between October 9 and October 21 in NOAA’s 1991-2020 normals, and earlier inland and north. Let them cure, pack them somewhere cool and dark, and look at them monthly until spring. The ground here freezes too hard for them to overwinter in the garden, even on the coast. So the real decisions are when to dig and how to store.
Do you have to dig them up in Maine?
The USDA Plant Hardiness Zone Map 2023 places Maine between zone 3b and zone 6a, which stretches from the northern interior to the mildest stretch of the southern coast. That system rests on a single variable, the average annual extreme minimum temperature. It tells you whether a plant can take the worst night of a typical year, not how wet the soil stays or how long the ground remains frozen. For tender tubers, the ground is what matters.
Dahlia tubers, canna rhizomes and gladiolus corms all come from warm climates. They store food underground, and that tissue turns to mush once it freezes. Where the ground stays unfrozen or freezes only at the surface, a thick mulch is enough to carry them through. Maine is not that place. At Portland, the mild end of the state, the mean daily minimum of the coldest month is 15.6°F, according to NOAA NCEI Climate Normals 1991-2020. That is more than 16 degrees below freezing on the average January night, and inland and northern Maine run colder still.
So the verdict is simple: lift all three every fall, in every part of Maine. There is no line inside the state where the answer flips to “leave them and mulch.” Some gardeners on the warmest stretch of coast try it anyway, and a few get away with it in a mild winter. One hard, snowless cold snap ends the experiment. Mulch slows the freeze without stopping it, and wet soil around dormant tubers is an invitation to rot even when the cold itself doesn’t do the damage.
What changes from one part of Maine to another is the date, not the decision. Colder ground, farther north or higher up, brings the first fall frost earlier, so the lifting happens earlier too. A dahlia bed in the western foothills may be ready to dig while a coastal bed is still in bloom.
Hardy bulbs are a different story. Tulips, daffodils and crocus want to stay planted through the cold, and Which Spring Bulbs Survive Your Winter sorts out which ones do. The broader Spring Bulbs section covers that side of the garden. Dahlias, cannas and gladiolus belong to the other group, the summer performers that have to be rescued before the ground locks up.
When to lift them
The signal is a frost that blackens the foliage. Dahlia and canna leaves go limp and dark almost overnight, and that is the plant telling you the growing season is over. Lift within a week or two of that frost. At Portland, where NOAA NCEI’s 1991-2020 normals put the first 32°F freeze between October 9 and October 21, that means roughly mid-October into early November. Treat those dates as the coastal window, not a calendar for the whole state. Inland and northern gardens get their first frost sooner, so the same one-to-two-week rule lands earlier there. The First and Last Frost Dates in Maine page gives the local picture for your town.
That frost range, by the way, is a probability band. NOAA’s figure marks where the chance of a 32°F freeze sits between 30 and 70 percent. Some years the freeze arrives before the range and some years well after it. Go by what the plants are doing in your yard rather than by the date on the calendar.
Waiting a few days after the frost is not laziness. While the foliage is still alive, the plant keeps moving energy down into the tubers, and the skins thicken and firm up. Tubers dug while the plant is still green are immature. Their skins are thin, their necks are soft, and they carry more moisture than they can shed in storage. Those tubers are the ones that turn up slimy and moldy by January. Lifting too early, costs you the very tubers you were trying to save.
The wait has a limit, though. Once the foliage has blackened, the clock is running, because a hard ground freeze will reach the tubers next. If the forecast is heading toward a deep freeze and your plants still haven’t been hit by frost, cut them back and lift anyway. A slightly immature tuber handled carefully beats a frozen one.
When you dig, cut the stalks back to short stubs first, which gives you a handle and keeps you from snapping necks. Push a garden fork into the soil well away from the clump, since dahlia tubers spread wider than most people expect, then lever the whole mass up gently. Cannas form dense, heavy clumps that take some muscle. Gladiolus corms sit shallower and come up easily with a trowel or fork.
Gladiolus are the one partial exception to the frost signal. Their leaves often yellow and brown on their own as the season winds down, and late plantings may still be green when the first frost hits. Lift them once the foliage has browned, whether the frost did it or the plant did.
Storing them over winter
Cure first, then clean lightly
Curing means letting the freshly dug roots dry in a sheltered, airy spot (a garage, a porch or a covered bench) until the skins feel dry to the touch. Keep them out of direct sun and out of rain, and never leave them where frost can reach them. Then brush off the loose soil. Skip the hose. A heavy wash leaves water trapped in crevices and raises the odds of rot. If you do rinse off stubborn clay, dry everything thoroughly before packing.
Trim away any obviously damaged or rotting pieces now, and label the clumps by variety while you still remember which is which. Labels written in pencil on a paper tag survive a winter in damp packing better than marker on plastic.
How the three differ
The target is the same for all of them: cool, dark, above freezing, and humid enough that nothing shrivels but dry enough that nothing rots. The balance shifts from one plant to the next.
| Plant | What you store | Packing | Moisture |
|---|---|---|---|
| Dahlias | Tuber clumps, left whole or lightly divided | Boxes or crates with barely damp peat, vermiculite or wood shavings | Slightly moist; the most prone to shrivelling if air is dry |
| Cannas | Thick rhizome clumps with short stalk stubs | Similar to dahlias, in crates or bins with lightly damp packing | Slightly moist; they dry out and wrinkle quickly and dislike chill |
| Gladiolus | Individual corms, old shriveled base removed, tiny cormels saved separately | Paper bags, mesh bags or open trays | Dry and airy; they rot fast if kept damp |
Gladiolus want the driest treatment of the three. After the first curing, pull off the old, withered corm from the bottom of each new one and let the fresh corms dry until they are hard. Stored in a humid box, they mold. Dahlias and cannas are fleshier and lose water steadily, so they need a little moisture in the packing to stay plump. The usual mistake is to overdo it. The packing should feel barely damp, not wet, and a squeezed handful should not leave your palm wet.
The monthly check
Plan to check them once a month from the day they go into storage until they go back into the ground in spring. Open the boxes, look and feel. Soft spots or a sour smell mean rot, so cut it away and let the cut surface dry. Wrinkled, leathery skin means the packing has dried out, so add a light misting to the medium, not the tubers. Mold on a corm usually means too much humidity or too little air, which a day in the open usually fixes. This ten-minute job is what keeps one bad tuber from spoiling its neighbors, and it is the step most often skipped.
What goes wrong
Rot is the big one. A rotted tuber feels soft or mushy and often smells sour, sometimes with white or gray mold on the surface. It comes from storing too wet, packing tubers before they cure, or lifting them before they matured. Cut out small bad spots with a clean knife and let the cut heal over. Toss anything that has gone soft through the middle. Prevention is curing properly, keeping packing barely damp, and giving the box some air.
Shrivelling is the opposite problem. The skin wrinkles and the tuber feels light and leathery. It happens when storage air is too dry or too warm, which is common in a heated basement. A mild case recovers with slightly more moisture in the packing. A tuber that has gone hard and hollow will not sprout.
Lifting too early, before the frost and before the plant has finished feeding its tubers, produces tubers with thin skins and soft necks. They may look fine in October and fail by midwinter. Wait for the frost to blacken the foliage, then lift within a week or two. The exception is a forecast for a deep ground freeze, which overrides the wait.
The last failure is leaving them in the ground one zone too far north, which in Maine means anywhere. Dahlias left in the bed often look fine under mulch all winter, then never appear in June. The digging in spring turns up brown, collapsed tissue where the tuber was. No amount of mulch fixes that, and storing them indoors is the cure.
Common questions
Can I leave dahlias in the ground at Portland with heavy mulch?
It is a gamble, and the numbers are against it. Even at Portland, the mild end of Maine, the coldest month has a mean daily minimum of 15.6°F (NOAA NCEI Climate Normals 1991-2020). Some winters are gentler, and some are not. Lifting costs a few hours each fall, while a lost collection takes years to rebuild.
What if the first frost comes late?
The Portland range of October 9 to October 21 is a central band, not a guarantee. If the frost hasn’t arrived and a deep freeze is in the forecast, cut the plants back and lift them anyway. Slightly immature tubers stored with extra care do better than tubers caught in frozen ground.
Should I wash the tubers before storing them?
Brushing off loose soil after curing is enough for most gardeners. If clay is caked on, a gentle rinse is fine, provided the tubers dry completely afterward. Water left sitting in crevices is a common starting point for rot.
When should I divide them?
Dahlias and cannas are usually easiest to divide in spring, when growth buds, called eyes, are visible and you can see where to cut. Gladiolus need no dividing, only removal of the old corm and the tiny cormels. When it is time to plant them back out, Planting Spring Bulbs in Maine covers timing for hardy bulbs, and more seasonal jobs are collected in the Maine guides.