In Portland and the milder ground west of the Cascades, dahlias, cannas and gladiolus can often stay put under a thick mulch. Where the soil freezes deeply, they have to come up. The signal is the first frost that blackens the leaves. In Portland that frost arrives between November 11 and November 27, so lifting runs from mid-November into the first part of December. Central and eastern Oregon lift earlier.
Do you have to dig them up in Oregon?
The USDA Plant Hardiness Zone Map 2023, built on 1991-2020 normals, runs Oregon from 4a to 9b. Hardiness zones rest on a single variable, the average annual extreme minimum temperature, so a dated recommendation needs a reference city, and Portland is the one used here. Its coldest month, according to NOAA NCEI Climate Normals 1991-2020, has a mean daily minimum of 36.2°F. That is above freezing. A few nights still dip below 32°F, which is why frost shows up in November, but the ground rarely freezes deep enough to reach a tuber set several inches down. In Portland and similar mild sites, leave dahlias, cannas and gladiolus in the ground under a thick mulch, and lift them everywhere the soil freezes deeply.
Plenty of Oregon gardeners fall outside that mild pocket, so the rest of this guide covers the lifting side. Other parts of the state differ a great deal from the Portland numbers, and the broader Oregon guides sort the state region by region.
Where does the line fall between leaving and lifting?
Roughly along the Cascades. West of them, the Portland pattern holds: mild winters, rain instead of deep cold, and soil that stays workable. Central and eastern Oregon are high desert, with a far shorter growing season and hard winter freezes. Tubers left there are exposed to frozen ground and will not come back. Higher elevations on the west side behave more like the east, and colder spots anywhere get their first fall frost earlier, so the lifting window moves earlier there too.
If your garden sits near the line, such as a foothill lot, a frost pocket or a north-facing slope, lift. Losing a season of tubers costs more than an afternoon with a garden fork. Your county extension office can tell you how deep the ground typically freezes at your elevation. Gardeners in eastern Oregon who want a neighboring-climate comparison can read about lifting tender bulbs in Idaho.
Does mulch work in a wet Oregon winter?
Cold is rarely what kills tubers on the west side. Rain does it. Dahlia tubers and gladiolus corms sitting in cold, waterlogged clay rot long before frost reaches them. Mulch of shredded bark, straw or leaves sheds some of that water and blankets the crown, but it cannot fix a bed that holds puddles. If your soil drains slowly, lifting is the safer call even in Portland.
Hardy bulbs such as tulips and daffodils follow different rules entirely. For those, Which Spring Bulbs Survive Your Winter sorts out what stays in the ground.
When to lift them
Wait for a frost that blackens the foliage. Frost shrivels the tops of dahlias and cannas overnight, and gladiolus leaves yellow and flop. That is the plant’s own message that the season has ended. For Portland, NOAA NCEI U.S. Climate Normals 1991-2020 put the first 32°F freeze between November 11 and November 27 (the 30-70% probability band). Lift one to two weeks after the frost blackens the foliage, which in Portland means mid-November into the first part of December.
Those dates belong to Portland and the lowlands west of the Cascades. Central and eastern Oregon get their first frost sooner, so the lifting window there arrives earlier, often well before Portland’s. Use your own first frost, not Portland’s, and check First and Last Frost Dates in Oregon for your area.
Why does lifting early cause rot in storage?
Foliage keeps feeding the tubers until frost ends it. During those last weeks the plant moves sugars down into the roots and corms, and the skins thicken. A tuber dug in September or early October, while the tops are still green, has thin skin and a high water content. It loses moisture fast, or it picks up fungus at a cut or bruise, and by January it has turned to mush in the box. The week or two after frost gives the tubers time to finish. It also lets the stems dry back so that cutting them is clean.
Waiting too long has its own cost. A hard freeze that reaches the ground can damage tubers, and long stretches of cold rain invite rot in the bed. Dig on a dry day, when the soil is crumbly instead of sticky.
How do you lift them without damage?
Cut dahlia and canna stems down to a few inches. Push a garden fork into the soil well outside the clump and lever it up gently, since dahlia necks snap easily and a broken neck will not sprout. Gladiolus corms lift with a fork or a trowel, and the dead tops can be cut off right at the corm. Shake off loose soil but leave the rest. If frost never comes before December, lift once the foliage has yellowed and collapsed on its own, because that is the same signal.
Storing them over winter
All three need the same three things: cure, clean lightly, store cool and dark. Cool means above freezing and out of any heated space. Dark keeps them from sprouting early. Slightly moist keeps them from shriveling without inviting rot. Where they differ is in how much moisture each one wants.
How do you cure and clean them first?
Lay the clumps in a sheltered spot out of the rain, such as a garage, a porch or a covered bench, for several days so the skins dry and any cuts seal. Brush off soil with your hands. Skip the hose, because wet tubers headed for a box are a recipe for mold. Cut off damaged pieces with a clean knife. Throw away anything soft, black or sour-smelling right now so it cannot spread.
How do dahlias, cannas and gladiolus differ in storage?
| Plant | What you store | Packing material | Moisture |
|---|---|---|---|
| Dahlia | Tuber clumps with a stub of stem | Barely damp peat, vermiculite or wood shavings in a box or crate | Slightly moist, never wet |
| Canna | Whole rhizome clumps, some soil left on | Barely damp peat or sawdust, or a paper bag | Slightly moist, since the fleshy rhizomes shrivel quickly |
| Gladiolus | Corms, old shriveled corm removed after curing | Mesh bag or paper sack, open to air | Dry, with good airflow |
Dahlias are the fussiest about moisture. Too dry and the tubers wrinkle, too wet and they rot. Cannas hold more water and do best with a little soil still clinging. Gladiolus corms, once cured dry, store like onions. They want airflow and a place where they will not sweat.
Label each box by variety or color before you close it. In April, a box of unlabeled brown lumps tells you nothing.
Store the boxes somewhere cool and dark that stays above freezing, such as an unheated garage, a basement or a closet on an outside wall. Then check them once a month through winter. That single habit saves more tubers than any packing material. Remove anything with mold or soft spots at once, and mist the packing material lightly if the tubers feel wrinkled. Hardy spring bloomers are a different story, and Spring Bulbs covers the ones that stay in the ground all year.
What goes wrong
Most losses come from four causes, and each leaves a clear mark on the tuber.
- Rot. Tubers turn soft, dark and sour-smelling, often with gray or white mold. It comes from storing wet, from packing material that never dried or from poor airflow. Cut away small spots, let the cut dry, and move the rest to a drier, better-ventilated box.
- Shriveling. Tubers wrinkle and feel light or hollow. The storage spot is too dry or too warm, so mist the packing material lightly and move the box somewhere cooler.
- Lifting too early. Thin-skinned tubers dug while the foliage was still green shrink or rot within weeks. Wait for the frost that blackens the leaves, then give them the extra week or two.
- Leaving them in one zone too far north. Frozen tubers turn to mush and nothing sprouts in spring. It looks like a bare patch where the dahlias used to be.
The last one deserves a closer look, because the line moves with your garden. In central and eastern Oregon, lift every year, since the soil there freezes. Gardeners in far colder climates such as Quebec treat tender bulbs the same way, with no exceptions. West of the Cascades, the choice depends on drainage as much as cold, which is why a raised bed with fast-draining soil can overwinter bulbs that a heavy clay bed cannot. Planting Spring Bulbs in Oregon explains how to match a planting spot to your drainage.
Common questions
Can I leave dahlias in the ground in Portland?
Often yes. Portland’s coldest month has a mean daily minimum of 36.2°F, so the ground rarely freezes deep. Add a thick mulch and make sure the bed drains well. Wet clay is a bigger threat than cold, and tubers in a soggy bed should come up.
What if frost has not come by December?
Lift once the foliage has yellowed and collapsed. The frost is only the usual trigger. What the tubers need is the plant’s own signal that growth has ended, and a dry day to dig.
Do I lift all three at the same time?
Roughly, yes. Dig all of them in the week or two after the first frost blackens the leaves. Gladiolus corms can come up as soon as the tops yellow. Keep each type separate when you store them, since dahlias and cannas want a slightly damp medium and gladiolus want dry air.
Do tulips and daffodils need lifting too?
No. Hardy spring bulbs stay in the ground through Oregon winters, and many need the cold. The lifting routine here applies only to tender summer bulbs. For help sorting which is which, see Spring Bulbs.