In Wyoming, dahlias, cannas and gladiolus come out of the ground every fall. Nights in Cheyenne’s coldest month average 18.1°F (NOAA NCEI 1991-2020 normals), far too cold for tender tubers, rhizomes and corms to sit in frozen soil. The cue is a frost that blackens the foliage. At Cheyenne the first fall frost arrives between September 24 and October 5, so lifting happens in the days after that frost, from early October into mid-October. For other seasonal jobs, browse the Wyoming guides.
Do you have to dig them up in Wyoming?
Yes, and the answer does not change from one corner of the state to another. The USDA Plant Hardiness Zone Map 2023 places Wyoming in zones 3a to 6a. That system is built on a single variable, the average annual extreme minimum temperature. Leaving these plants in the ground under mulch only works where the soil does not freeze deeply, and nowhere in that range does it get that easy. Lift all three every fall, whether the garden sits in a sheltered valley or on open high plains.
The Cheyenne numbers show why. NOAA’s 1991-2020 normals put the mean daily minimum of the coldest month at 18.1°F. That is an average, so cold snaps run well below it, and the soil spends long stretches frozen. Dahlia tubers, canna rhizomes and gladiolus corms are mostly water. When that water freezes, the cells burst, and the tissue turns to gray mush by the time the soil thaws in spring.
All three come from warm climates. They behave like perennials in mild-winter regions, which is where the “just mulch them” advice in a lot of garden writing comes from. That advice was written for somewhere else. Mulch slows the rate at which ground freezes, but it cannot stop a Wyoming winter from reaching a tuber. An occasional survivor in a sheltered bed doesn’t change the odds, and a plant that comes back one year in five is not a plan.
Hardy spring bulbs are a different story. Tulips, daffodils and many of their relatives need the winter chill and stay in the ground, and Which Spring Bulbs Survive Your Winter sorts out which ones. The three plants here belong in the other category, the tender bulbs that take a winter vacation indoors.
Elevation moves the calendar, not the verdict. The Cheyenne station sits near 6,000 feet and NOAA’s normals there show roughly 130 frost-free days. At higher elevations frost is possible in any month. Higher and farther north, the first fall frost comes earlier, so lifting moves earlier. Lower and warmer parts of the state get a little more time before the same job is due. In every case the plants come up and the storage season begins.
When to lift them
The signal is a frost that kills the top growth. Dahlia leaves and stems turn black and limp, canna foliage collapses into a dark mush, and gladiolus leaves go brown and flop. At Cheyenne, NOAA’s 1991-2020 normals (station USW00024018) put the first 32°F freeze in a band from September 24 to October 5, the stretch where the probability of a freeze runs between 30 and 70 percent. Lift a week or two after the first frost that blackens the foliage, which in Cheyenne means early to mid-October.
That is a reference-city window, not a statewide date. Gardeners in colder, higher or more northern parts of Wyoming see frost sooner and should lift sooner. Those on lower, warmer ground can wait a bit longer. The surest way to place yourself is your own first frost, and First and Last Frost Dates in Wyoming gives the dates for towns around the state.
Why the wait matters
A frost on the leaves does not mean the underground part is finished. While green growth lasts, the plant keeps sending sugars down into the tuber, rhizome or corm. A frost cuts off the supply and signals dormancy, and the storage organ then firms up its skin over the next several days. Lift too soon and you get thin-skinned, watery pieces. They lose moisture fast, and the same wounds that heal on a mature tuber become entry points for rot on an immature one. Gardeners call this the classic failure of the eager lifter: the tubers looked fine in October and were soft by January.
Waiting has a limit. A week or two after the frost is plenty, because a long run of hard freezes will eventually chill the soil around the roots, and cold, wet ground invites rot of its own. If a hard freeze is forecast and no killing frost has arrived yet, covering the plants with a sheet for a few nights buys time and keeps the foliage working. Gladiolus can start browning before frost, but in Wyoming’s short season many are still green when the first freeze comes, so frost is the more reliable cue.
How to lift
Pick a dry day. Cut the stems down to a short stub, then work a garden fork into the soil well outside the clump and lever it up. Dahlia tubers snap at the neck, and a broken neck means a tuber that will not sprout, so loosen the soil more than feels necessary. Cannas form tough, heavy rhizome clumps that take real muscle. Gladiolus corms pull up more easily, often with a small crop of baby corms (cormels) clinging to the base.
Storing them over winter
Curing and cleaning
Curing comes first. Spread the lifted pieces in a sheltered, airy spot out of direct sun and rain, such as a garage bench or porch, until the surface of the skin feels dry. Then clean lightly. Knock off the loose soil with your hands or a soft brush and leave the rest, because scrubbing scars the skin and a soaked tuber starts a rot problem before storage begins. Trim any damaged tissue with a clean knife.
The storage spot matters as much in Wyoming as anywhere. The Cheyenne coldest-month minimum of 18.1°F means an uninsulated garage or shed will freeze, and frozen tubers do not recover. An interior basement, a cool closet or an insulated garage corner that stays above freezing, dark and steady, works best.
What each plant wants
| Plant | What you store | Packing | Moisture | Watch for |
|---|---|---|---|---|
| Dahlias | Tuberous roots, with a piece of the crown | Boxes or crates with lightly damp wood shavings, vermiculite or peat | Slightly moist, never wet | Wrinkling (too dry), soft spots or mold (too wet) |
| Cannas | Rhizome clumps | Boxes with barely damp peat or shavings, left in larger pieces | Slightly moist, a bit more forgiving | Drying out into hard, light chunks, or sour-smelling rot |
| Gladiolus | Corms, once cured and separated from the old shriveled corm | Paper bags, mesh bags or open trays with air around them | Dry and airy | Mold, soft corms, or rubbery shriveling |
Dahlias and cannas want a little humidity because their fleshy tissue dries out in a heated, low-humidity house. Gladiolus corms are the opposite. They store like onions, with air moving around them, and damp packing is the quickest way to lose a bag of them. Leave the baby cormels in their own labeled bag if you want to grow them on.
The monthly check
Storage fails slowly and quietly, which is why checking the containers once a month is the step that saves them. Open each box, look and squeeze gently. Cut away any soft or moldy spot with a clean knife, let the cut dry, and repack in fresh material. If the pieces look wrinkled, mist the packing lightly. If you see mold, loosen the packing or add dry material. Five minutes a month beats replacing a collection in May.
What goes wrong
Most losses trace back to four mistakes, and the best protection is a calendar habit: lift every year, a week or two after the foliage-blackening frost. Each mistake leaves a recognizable sign.
- Rot: tubers feel soft or mushy, smell sour, or grow gray or white mold. The cause is usually packing that is too wet, poor airflow or lifting before the skin matured. Prevent it with thorough curing, slightly damp (not wet) packing and the monthly check, and cut out affected spots early.
- Shrivelling: pieces turn wrinkled, light and rubbery. The storage space is too dry or too warm. Mist the packing lightly, move the box somewhere cooler and keep the packing material, not the tuber, damp.
- Lifting too early: small, thin-skinned tubers that wilt or rot within weeks. Wait for the frost that blackens the foliage, then another week or two.
- Leaving them in the ground: the plants vanish in spring and you find mush where the clump was. Wyoming’s USDA zones run from 3a to 6a, and none of that range is mild enough to make mulch a reliable shield.
Mislabeling is the quiet fifth problem. Dahlia colors look identical as bare tubers, so tag them in the field, before you lift, with a note that survives damp packing.
Common questions
Can I leave dahlias in the ground in Cheyenne under thick mulch?
Not safely. With the coldest month averaging nightly lows of 18.1°F, the soil freezes, and mulch only delays that. Lift them each fall and store them indoors.
Do gladiolus need frost before I dig them?
Not strictly, since the foliage can yellow on its own, but in Wyoming’s short season many are still green when the first fall freeze arrives. Use the frost that browns the leaves as your cue, then give the corms a week or two before lifting.
What if a hard freeze comes before the plants have finished growing?
Cover them with a sheet for a few nights if only one cold night is forecast. If the freeze is likely to last, cut them back and lift. Tubers from a plant cut early may be thinner, so cure them well and give them extra attention at the monthly check.
When do they go back outside in spring?
After the last spring frost, which comes later at higher, colder elevations. Start dahlias and cannas in pots indoors if you want an earlier start. For the hardy bulbs that stay in the ground all winter, see Planting Spring Bulbs in Wyoming and the wider overview of Spring Bulbs.