Lift dahlias, cannas and gladiolus after a frost has blackened the foliage, then dig within one to two weeks. Around Seattle, the first fall frost typically arrives between November 13 and November 30, according to NOAA’s 1991-2020 Climate Normals, so the digging window runs from late November into mid-December. East of the Cascades the frost comes sooner and the digging moves up with it. Whether you dig at all depends on which side of the mountains your garden sits.
Do you have to dig them up in Washington?
In the mild lowlands west of the Cascades, dahlias, cannas and gladiolus can stay in the ground under a thick mulch; east of the Cascades, where the ground freezes deep, all three must come up. That split matters more than any date on the calendar, because the same plants that come through a Seattle winter turn to mush in a high-desert freeze.
The USDA Plant Hardiness Zone Map 2023, built on 1991-2020 normals, rates Washington from 4a to 9a. A hardiness zone rests on a single variable, the average annual extreme minimum temperature, so a range that wide tells you the state has very different winters in different places. The maritime lowlands west of the Cascades sit toward the warm end of it. The interior east of the mountains runs far colder, and so do higher elevations on either side.
Can dahlias stay in the ground around Seattle?
Usually, yes. NOAA’s 1991-2020 Climate Normals for the Seattle station put the mean daily minimum of the coldest month at 37.1°F. That is above freezing. In a typical winter a few inches of shredded leaves or bark mulch adds a cushion for the cold snaps that do slip through.
The threat in western Washington is water. Winter rain on heavy clay or poorly drained beds keeps soil cold and saturated for months, and that is where tubers rot in place. Dahlias and cannas in raised beds or sandy, fast-draining soil have the best odds. Gladiolus corms are usually the first to give out.
Average temperatures also hide the odd hard freeze. Many western Washington gardeners hedge by leaving most of the planting in the ground and lifting a few clumps of anything they cannot replace. Lifting is also the easiest way to divide crowded dahlia and canna clumps, which is a good reason to dig even where winter would be survivable.
What about eastern Washington and higher ground?
East of the Cascades the land is high desert with a much shorter growing season, earlier fall frosts and winters cold enough to freeze the soil well below planting depth. Mulch will not save a dahlia tuber there. The same goes for foothill and mountain gardens on the west side. Anywhere that winters are colder than the Seattle lowlands, treat all three as plants that must be lifted, and lift them earlier in fall than the Seattle window below. For other seasonal jobs in your part of the state, the Washington guides collect local timing, and your county extension office can confirm the first-frost habits of your specific valley.
When to lift them
The signal is a frost hard enough to blacken the foliage. A light touch that leaves some leaves green does not count. Once the tops turn black and limp, dig one to two weeks after that frost, which around Seattle works out to roughly late November through mid-December. That timing comes from the first-frost band of November 13 to November 30, the stretch where NOAA’s 1991-2020 normals put the odds of a first 32°F freeze at the Seattle station between 30 and 70 percent. It is a window, not a deadline. Frost dates for other towns are laid out in First and Last Frost Dates in Washington, and colder spots will see the signal earlier than Seattle does.
Why not lift dahlias early?
Because the tubers are not finished. Until frost kills the top growth, the leaves keep sending sugars down into the roots. After the foliage dies, a short rest in the ground lets the skins toughen and the starch settle. Tubers lifted while the plant is still green have thin skins and a lot of water in them. They look fine on the day you dig them. In a box in the garage, they go soft and moldy by midwinter.
Cannas behave the same way. The rhizomes need the full season to fill out, and a rhizome dug before frost has less stored energy to restart in spring. If a gardener lifts early just to be safe, the tubers pay for it.
Gladiolus follow their own clock. They do not need a frost at all. Lift the corms once the leaves have turned yellow and begun to brown. Digging corms with green leaves still attached leaves them underdeveloped.
How do you lift them without damaging the tubers?
Pick a dry day, or at least a gap between rain showers, since western Washington autumn soil is often soaked. Cut dahlia and canna stems down to a short stub. Push a garden fork into the soil in a wide circle well away from the crown, then rock it to loosen the ground and lift the whole clump. Dahlia tubers snap off at the neck with very little force, so never pull on the stem.
Label each clump before you set it aside, especially if you grow more than one color. For gladiolus, loosen the soil beside the row and lift the corms by hand or with a fork, then trim the dead foliage off. If the window passes and no frost has arrived, cold rain and shortening days will eventually collapse the foliage anyway. Dig then, rather than leaving tubers sitting in sodden ground.
Storing them over winter
Three steps cover all three plants: cure, clean lightly, then store cool, dark and slightly moist so nothing rots and nothing shrivels. Check the stored bulbs once a month through winter, because that single habit rescues more tubers than any packing material does.
How do you cure and clean them?
Curing means letting the surface dry in a sheltered, airy spot out of sun, rain and frost, such as a garage bench or covered porch, until the skin feels dry and firm. The soil that clings to the clump should dry enough to crumble away. Brush off loose dirt with your hand or a soft brush. Skip the scrubbing and the hose. A bruised or scraped skin is an open door for rot, and tubers packed wet will spoil.
Gladiolus corms need a bit more cleanup. Set aside the small cormlets if you want to grow more. Let the corms dry in a well-ventilated place until the husks are papery.
Do dahlias, cannas and gladiolus store the same way?
Close, but not the same. Dahlia tubers and canna rhizomes are fleshy and lose moisture quickly, so they want a little dampness around them. Gladiolus corms hold their water, and in damp packing they mold. The table lays out the differences.
| Plant | What you store | Packing | Moisture | Warning sign |
|---|---|---|---|---|
| Dahlia | Clump of tubers | Ventilated box with barely damp peat, wood shavings or vermiculite | Slightly moist | Wrinkled skin means too dry; soft spots or mold mean too wet |
| Canna | Rhizome clump | Box or crate with lightly damp packing, or a pot of just-moist soil | Slightly moist | Shriveled, hard rhizomes mean too dry |
| Gladiolus | Corms | Paper or mesh bags, or trays in a single layer | Dry and airy | Mold or soft corms mean too humid |
All three want a cool, dark place that stays above freezing. In the Seattle area, with a coldest-month mean daily minimum of 37.1°F (NOAA NCEI 1991-2020), an unheated garage or shed can work through a normal winter, though a hard cold snap can get in. East of the Cascades garages and sheds often freeze, so a basement, a closet against an interior wall or an insulated crawl space is the safer spot. A heated room is too warm, and the tubers will wake up early.
On each monthly check, lift the lid, look and feel. Firm and plump is the goal. If the packing is bone dry and the tubers are wrinkling, mist the packing lightly. If you see condensation, mold or a sour smell, open the container, remove the damp medium and cut away any rotted spots down to clean, firm flesh before you repack.
What goes wrong
Four problems account for most lost tubers. Each one is easy to see if you look and easy to prevent if you know what causes it.
How do you spot rot and shriveling?
Rot shows up as soft, dark patches, often with a sour smell and sometimes a fuzz of gray or white mold. It starts at the neck of a dahlia tuber or at a wound on a rhizome. Packing that is too wet, tubers lifted wet, and containers with no air all cause it. Curing properly and checking monthly prevent most of it, and tubers that feel soft or smell sour should be cut back to firm, clean flesh or thrown out, since a rotting piece can spoil the rest of the box.
Shriveling is the opposite. The skin wrinkles, the tuber feels light and rubbery, and eventually it turns hard and will not sprout. Air that is too dry or warm, or packing with no moisture at all, causes it. A light misting of the packing and a cooler spot stop it if you catch it early.
What if you dug too early or left them in too long?
Tubers lifted before frost has done its work usually look healthy for a few weeks, then collapse in storage with soft necks and mold. The remedy comes next year. Wait for the blackened foliage, then give the clumps their one to two weeks. Gladiolus are the exception, since they signal readiness with yellowing leaves rather than frost.
Leaving plants in the ground one zone too far north is the costliest mistake. A gardener east of the Cascades who copies a Seattle neighbor’s mulch-and-leave routine finds mush in spring, because deep soil freezing kills tubers outright. If your winters are colder than the western lowlands, lift them every year. The local county extension office can tell you how cold your valley or hillside runs.
Common questions
What if frost has not come by the end of the window?
Watch the plants instead of the calendar. Cold rain and short days will eventually collapse dahlia and canna foliage even without a freeze. Once the leaves have gone limp and dark, lift the clumps. Leaving tubers in cold, saturated ground in western Washington risks rot.
Do tulips and daffodils need lifting too?
No. Hardy spring bulbs stay in the ground through winter and need the cold to bloom. Which Spring Bulbs Survive Your Winter sorts out which ones are truly hardy, the broader Spring Bulbs section covers the full range, and Planting Spring Bulbs in Washington covers fall planting in the state.
When can stored bulbs go back out in spring?
After the last spring freeze, once the soil has warmed. A mild frost date in western Washington does not mean an early planting date, because cold, wet soil and low spring light hold tender bulbs back well past the last freeze. Tubers set into cold mud sit and rot. Start them in pots under cover if you want a head start.
Should I wash the tubers before storing them?
Brushing off loose soil is enough. If you do rinse a clump to see the eyes or divide it, let it dry fully before packing, because any leftover moisture on the skin invites rot. Divide dahlia clumps in spring, when the eyes are easier to find, so each piece carries a bit of crown.
Related guides
- When to Dig Up Dahlias, Cannas and Gladiolus in Oregon
- When to Dig Up Dahlias, Cannas and Gladiolus in Idaho
- When to Dig Up Dahlias, Cannas and Gladiolus in West Virginia
Sources : dahliamayflowerfarm.com | dahlias.com