Dahlias and cannas go into storage in New York after the first frost that blackens their leaves, while gladiolus can come up once their leaves yellow, often before frost. In New York City, the first fall freeze typically arrives between November 14 and November 27, so lift dahlias and cannas after it. Upstate, frost comes far earlier, and the digging moves up with it. Leave these plants in the ground through a New York winter and the tubers will most likely turn to mush by spring.
Do you have to dig them up in New York?
In practice, yes. The line between “stay in the ground under mulch” and “come up for winter” falls south of nearly anywhere in the state. The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) places New York between zones 3b and 7b. That range covers the whole state, so a gardener in the Adirondacks and one in the city live in very different winters. Yet even at the milder end, the mean daily minimum of the coldest month in New York City is 27.9°F, according to NOAA’s 1991-2020 climate normals. The average coldest night is below freezing, and the soil freezes with it. So plan to lift all three every year, anywhere in New York.
The plants themselves explain the rule. Dahlias grow from tuberous roots, cannas from thick rhizomes, and gladiolus from corms. All three come from warm regions, and none of them has the tissue to take a hard freeze. Ice crystals rupture the cells, and the damage shows up as a gray, watery mush the following spring. Cold, wet soil does harm even before the ground freezes solid, because a swollen tuber sitting in saturated ground is an easy target for rot.
Which part of New York is mildest?
The warmest readings come from the New York City area, but the city is a dense urban site, and its figures flatter the rest of the state. Upstate New York and the Adirondacks see frost far earlier in fall and later in spring, with deeper, longer-lasting frozen ground. A gardener there has even less room to gamble than one in the five boroughs.
Can you gamble on a deep mulch?
Some gardeners in the mildest pockets leave a canna clump under a thick blanket of leaves or straw and get lucky in some winters. A mild winter proves nothing about the next one, and one hard stretch can kill every tuber left out. If you want to test it, treat it as an experiment: leave one clump, and store the rest of your stock indoors as insurance.
Hardy bulbs follow different rules. Tulips, daffodils and crocus want the cold, and they stay put. For how those compare with tender types, see Which Spring Bulbs Survive Your Winter, and for the broader picture, Spring Bulbs.
When to lift them
Watch the plants. The signal is a frost cold enough to turn dahlia and canna foliage black and limp, which gardeners call a killing frost. Lift dahlias and cannas within about one to two weeks after that frost (gladiolus can come up earlier, as described below). In New York City, NOAA’s 1991-2020 normals put the first 32°F freeze between November 14 and November 27 (the 30 to 70 percent probability band at Central Park).
Upstate gardeners should not borrow those dates. Frost reaches the Adirondacks and the colder parts of the state well ahead of the city, and fall jobs move earlier with it. Lift when your own foliage turns black, and use the calendar only as a rough guide. Your county’s frost dates, laid out in First and Last Frost Dates in New York, show how far your garden sits from the city’s window.
Why not lift earlier?
Tops that still look healthy are still feeding the underground parts. While the foliage is green, the plant keeps moving energy into the tubers, and the skin thickens and toughens. A killing frost ends that process, and the week or two afterward gives the tubers time to finish maturing. Dig during that stretch and you get tubers with thin skin and high moisture. Cuts and scrapes heal slowly on them, and in storage they rot, usually starting at the crown or at a broken neck.
Dahlias are fussier than the other two. Their new shoots form at the crown, where the tuber meets the old stalk, and that spot rots first if it is wet or damaged. The neck is also thin and breaks easily, and a tuber with a broken neck will not sprout. That is one more reason to let the plant finish before you dig.
What about gladiolus?
Gladiolus follow a slightly different clock. The leaves yellow and fade on their own, often before the first killing frost, and the corms can come up at that point. Waiting for a hard freeze gains little and risks frozen soil around the corms. Many gardeners lift gladiolus first, then cannas and dahlias.
How do you lift them without damage?
Cut the stalks back to a few inches above the soil. Choose a dry day, push a garden fork into the ground well out from the stem (the tubers spread wider than you expect), and ease the clump up from below. Never pull on the stalk. Shake off the loose soil and move the clumps to a shaded, sheltered spot for curing.
Storing them over winter
Storage comes down to three steps: cure, clean lightly, and store cool, dark and slightly moist. Cool means a place that stays above freezing but well below room temperature, such as an unheated basement, a root cellar or an insulated garage that never freezes. Dark keeps the tubers from sprouting early. Slightly moist keeps them from drying into hollow shells, while too much moisture invites rot. Many losses come from getting that balance wrong.
How do you cure and clean the tubers?
Curing means letting the surface dry in a sheltered, airy spot out of direct sun, until the skin feels dry and the cut stalk ends have sealed. Dahlias and cannas need a short stretch of this, while gladiolus corms need longer, until their husks turn papery. Then brush or rub off loose soil. A light cleaning is enough, since scrubbing and soaking add moisture and strip the protective skin. Cut away any soft or damaged parts first, and discard anything that is already mushy.
How do dahlias, cannas and gladiolus differ in storage?
Dahlias and cannas keep best in a barely damp medium. Gladiolus want the opposite: dry, airy storage.
| Plant | What you store | Storage setup | Moisture |
|---|---|---|---|
| Dahlia | Clumps of tuberous roots, divided now or in spring | Crates or boxes, packed in peat moss, vermiculite or wood shavings | Barely damp, never wet |
| Canna | Thick rhizome clumps, kept large | Boxes or paper bags with slightly damp packing material | Barely damp; large clumps resist drying better than small pieces |
| Gladiolus | Corms with the old shriveled corm and the tiny cormels removed | Mesh bags, paper bags or open trays | Dry, with good airflow |
Dahlia clumps are easiest to divide in spring, when the eyes are visible and swollen. Cannas do best stored in big clumps, because small pieces dry out quickly. Gladiolus corms should go into storage clean and dry, with the spent old corm snapped off the bottom.
How often should you check stored tubers?
A shelf of tubers can look fine from across the room while one rotten piece spreads to its neighbors. Check them regularly through the winter. Pick up a few from each container and press gently. Firm and plump is right. Soft, smelly or moldy tubers go in the trash, and surrounding ones get a wipe and a bit more air. Wrinkled ones need a light mist on the packing material. This is quick, and it often saves much of the stock.
What goes wrong
Almost every failure traces back to one of four causes, and each leaves a clear sign on the tuber. Here is what to look for and how to head it off.
Why do stored tubers rot?
Rotten tubers feel soft or mushy and often smell sour, with gray or white mold on the surface. The cause is excess moisture, poor airflow or damage that never healed. Prevention starts at lifting: dry the tubers properly, pack them in barely damp material (not wet), and give the container some air. Remove a rotting piece right away. If the rot is small, cutting back to firm, healthy tissue sometimes saves the rest.
Why do they shrivel?
Shrivelled tubers look wrinkled, leathery and light for their size, because the storage spot is too dry or too warm. A tuber that is wrinkled but still firm at the center will usually sprout, so lightly mist the packing material and move the box somewhere cooler. One that is hollow and papery is finished.
What happens if you lift too early?
Tubers dug while the foliage is still green have soft skin and have not finished maturing, so they rot or shrivel in storage even when everything else is done right. The cure is patience. Wait for a frost that blackens the foliage, then lift within the following week or two.
What if you leave them in the ground one zone too far north?
The result shows up in May. The soil warms, nothing comes up, and when you dig down you find mush or empty skins. This trap catches gardeners who moved from a milder state, or who had one easy winter and assumed it was the norm. Anywhere in New York, the safe move is to lift. A mulched clump that survives in a mild year is luck, and a hard winter ends it.
Common questions
Can dahlias stay in the ground in New York City?
Plan on lifting them. The city’s coldest-month nights average 27.9°F (NOAA, 1991-2020), so the ground freezes, and a wet, cold soil rots tubers even when the cold is not extreme. A few gardeners in the mildest, sheltered spots overwinter a mulched dahlia or canna clump in easy winters, but that is a gamble, not a method.
What if the first frost comes late?
Wait for it. The first killing frost in New York City arrives between November 14 and November 27 in a typical year, and some years run later. Keep the plants going until the foliage blackens. If the ground freezes hard before that happens, cut the tops back and lift anyway, since tubers in frozen ground are at risk.
Do you wash tubers before storing them?
Only lightly, and only after they have cured. Brush off the dried soil and trim away damaged parts. Washing leaves the tubers wet and rinses off the skin that protects them from rot, which is why most growers avoid it.
Is lifting time the same as planting time for spring bulbs?
The two jobs overlap in fall, but they follow different logic. Tender bulbs come up after frost, while tulips and daffodils go into cool soil around the same weeks. For that side of the garden, see Planting Spring Bulbs in New York, and for more regional timing, browse the New York guides.