In most of Maryland, yes: dahlias, cannas and gladiolus corms come out of the ground every fall. The signal is the first hard frost that blackens the foliage. Around Baltimore that frost arrives between October 26 and November 5, according to NOAA’s 1991-2020 normals. Lift the plants within a week or two after it, cure them, and store them cool and barely damp until spring. The reasoning behind that answer, and what changes in the mountains or on the Shore, is below.
Do you have to dig them up in Maryland?
Maryland sits between USDA zones 5b and 8a on the USDA Plant Hardiness Zone Map 2023, and the verdict depends on where you fall in that spread. Where the ground does not freeze deeply, tubers and rhizomes can overwinter under mulch. Where it does, they have to come up. Most of the state is in the second group, so plan on lifting all three every fall, starting after the first killing frost in late October or November.
The zone number needs a caveat. The USDA system is built on one variable, the average annual extreme minimum temperature. It tells you about the single worst night of a typical winter, not how many weeks the soil stays cold. A better everyday gauge is the mean daily minimum of the coldest month. At Baltimore, NOAA’s 1991-2020 climate normals put that figure at 25.4°F. That is well under freezing, and it describes a normal January night, not a freak one.
Where the line falls
Baltimore is the reference point here, and other parts of the state differ. Western Maryland (Garrett and Allegany counties) is mountainous and colder. Frost arrives there earlier than in the Baltimore range, so the lifting calendar shifts earlier too, and leaving anything in the ground is not a serious option. The Eastern Shore runs milder, and the mildest pockets toward the bay are the only places where mulching becomes a real conversation. Even there, it is a bet on one winter at a time.
If you are not sure which side of that line you are on, look up your own zone on the USDA map before gambling a season’s worth of tubers. The same logic sorts hardy bulbs from tender ones, which Which Spring Bulbs Survive Your Winter walks through for the daffodils and tulips that do stay put.
What mulch can and cannot do
Mulch slows the cold. It does not stop it. A thick blanket of shredded leaves keeps the top few inches of soil from swinging between freeze and thaw, but a long cold snap eventually works through it. Dahlia tubers and canna rhizomes are mostly water. When that water freezes, the cells burst, and the result in spring is a mushy lump that never sprouts.
Wet soil is the second threat, and in Maryland it may be the bigger one. Heavy clay, common across the Piedmont, holds cold water around tubers for weeks. Tubers can rot there even in a winter that never gets truly hard. That is why gardeners in the milder parts of the state who do try overwintering in the ground usually do it only in raised, fast-draining beds.
When to lift them
The cue is the weather, not the calendar. A frost hard enough to turn dahlia and canna foliage black signals that the plant has stopped feeding the root system. Lift within about a week or two of that frost, and the tubers have had a short stretch to firm up and mature. At Baltimore, NOAA’s 1991-2020 normals put the first 32°F freeze between October 26 and November 5 (the 30 to 70 percent probability band). So expect to lift from late October into November, a week or two after the first frost blackens the leaves.
Reading the frost, and your corner of the state
Treat that range as a Baltimore-area figure. Gardeners in Garrett and Allegany counties should expect the blackening frost, and therefore the digging, to come earlier. On the Eastern Shore it may come later. A thermometer on the porch beats any printed date. If you want the full picture for your county, First and Last Frost Dates in Maryland lays out the first and last freeze windows.
The three plants do not all follow the frost the same way. Dahlias and cannas wait for it. Cut the blackened stems back to a short stub and lift carefully with a garden fork set well outside the clump, because the tubers spread wider than most people expect. Gladiolus corms follow their own clock, and many gardeners dig them when the leaves begin yellowing and browning, which can happen before a frost. Leaving glads in too long invites thrips and rot, so do not wait on a frost that may be weeks away.
Why lifting early backfires
Digging the moment the plants look tired feels responsible. It usually backfires. Green foliage is still sending sugars down to the roots, and tubers pulled early are thin-skinned and underfed. They shrivel faster than mature ones, and their skins are slow to heal around cuts and breaks, which gives rot an entry point. A tuber dug before the plant has finished maturing it often looks fine in November and is a soft, gray-brown mess by January.
The other side of the margin matters too. Waiting a week or two after the frost is fine. Waiting for the ground to freeze solid is not. A soil freeze reaches the crowns and kills them, and a stretch of cold, soaking rain after the foliage dies is almost as bad. Pick the first dry day after the frost, let the clumps sit in the open air for a few hours, and move them indoors before dark.
Storing them over winter
Storage does three jobs: cure the skins, hold the right moisture, and keep temperatures cool but frost-free. Get those three right and the details by plant are minor. Get one wrong and the whole stash suffers. A cool, dark, frost-free spot such as an unheated basement, a root cellar or an insulated garage works well. A heated room is usually too warm and too dry.
Curing and cleaning
After lifting, shake or brush off loose soil and leave the clumps somewhere sheltered and airy so the skins dry and toughen. Skip the scrubbing. Soil in the crevices does no harm, and aggressive washing damages skins and leaves moisture where you do not want it. If you do rinse (some gardeners do, to inspect for damage), dry everything completely before it goes into storage. Dahlia necks, where the tuber meets the stem, are brittle and break easily. Handle them like glass.
How the three differ
Dahlias and cannas want slight moisture, because their fleshy tissue shrivels in dry air. Gladiolus corms want to be dry and well ventilated, because they rot in anything damp. That difference is the reason not to throw all three into one box.
| Plant | What you store | Curing | Packing |
|---|---|---|---|
| Dahlias | Clumps of tubers, divided now or in spring | Air-dry until the skins feel dry to the touch | Barely damp peat moss, vermiculite or wood shavings, in a ventilated container or paper-lined box |
| Cannas | Whole rhizome clumps with a little soil left on | Brief air-dry, then keep slightly moist | Lightly damp medium or paper-wrapped, never soaking |
| Gladiolus | Corms, with the old shriveled corm removed and the small cormels saved | Longer and drier than the others, in a warm airy spot | Dry, in mesh bags or open trays so air moves |
The monthly check
Storing them is half the job. Looking at them is the other half. Check the boxes once a month through winter, and handle each piece. Soft, sticky or smelly spots mean rot starting. Cut it out with a clean knife, dust the cut with a little sulfur or let it dry, and move the piece to a drier spot. Wrinkled, rubbery tubers mean the packing medium is too dry. Mist the medium lightly, not the tubers themselves. Gladiolus corms that feel clammy need more airflow.
That ten-minute monthly look is what separates a spring full of sprouting eyes from a box of compost. Catching one rotting tuber in January saves the ones touching it.
What goes wrong
Most winter losses trace back to four mistakes, and each one leaves a recognizable clue.
Rot and shrivel
Rot shows up as soft, dark patches, a sour smell, and sometimes gray or white mold. The usual causes are packing too wet, sealing tubers in plastic with no air, or storing before the skins dried. Prevent it with a barely damp medium, a ventilated container, and the monthly check. Shriveling is the opposite problem. Tubers go wrinkled and light, like a raisin, because the air or the packing is too dry. Lightly dampen the medium, or move the box to a spot with steadier humidity such as a basement corner away from a furnace. Once a tuber has lost most of its moisture it rarely recovers, which is why catching it early matters.
Lifting too early, or leaving them in a zone too far north
Early lifting produces tubers that look fine and fail in storage, as covered above. The cure is patience: wait for the frost to blacken the foliage, then lift within a week or two. The fourth mistake is leaving them in the ground on the strength of a neighbor’s success or a mild winter or two. Maryland’s range runs from the cold mountains of the west to the milder Shore, and a method that works near the bay can fail in the hills. One cold January can wipe out a whole planting. The same lesson applies in reverse to bulbs meant for the ground. The Planting Spring Bulbs in Maryland page covers the ones that can stay, and the broader Spring Bulbs section sorts them by hardiness.
Common questions
Can I skip digging if I mulch heavily?
In most of Maryland, that is a poor bet. Baltimore’s coldest-month mean minimum is 25.4°F, and the colder parts of the state run lower. Mulch softens the swings but does not keep the soil above freezing through a long cold spell. The mildest pockets toward the bay are the exception, and even there good drainage matters as much as mulch depth. If you want to test it, leave a few spare tubers in place and lift the rest.
What if the first frost comes late?
Frost dates are probabilities, not promises. NOAA’s range for Baltimore, October 26 to November 5, marks where freezes become likely, and some years run past it. If the foliage declines or gets damaged by disease, you can lift anyway, but the tubers will be less mature. Otherwise, keep waiting for the blackening frost. For ranges across the state, the Maryland guides are a good place to start.
Do I have to wash the tubers?
No. Brush or shake off loose soil and let them dry. Washing is optional, and only worthwhile if you want a close look for damage. If you wash, dry them completely before storing. Moisture trapped against the skin is one of the quickest routes to rot.
Should I dig gladiolus at the same time as dahlias?
Not necessarily. Gladiolus corms are usually lifted when the foliage yellows and browns, which can come before the first frost. Dahlias and cannas wait for the frost to blacken the leaves. Cure the corms drier and longer than the dahlias, store them in open mesh or trays, and keep the small cormels if you want to grow more.