Dig dahlias, cannas and gladiolus after the first frost has blackened the foliage, and only where frost actually arrives. In Los Angeles and across the frost-free coast and south, nothing has to come out of the ground. In Northern California, the Central Valley and the Sierra, the work starts with the first hard freeze. The colder and higher your garden sits, the earlier that freeze comes, and the sooner you will be out there with a garden fork.
Do you have to dig them up in California?
California has no single answer, and the hardiness map shows why. The 2023 USDA Plant Hardiness Zone Map (a system built on one variable, the average annual extreme minimum temperature) places the state anywhere from 5a to 11a. That is a territory-wide range, not a zone you can plan around. Where the ground does not freeze deeply, dahlias, cannas and gladiolus can stay in the soil under mulch; where it does freeze, they come up every fall. Other parts of the state sit on the opposite side of that line from Los Angeles, so one city’s habits should not be copied statewide.
The frost-free coast and south
Take Los Angeles as the reference. NOAA’s 1991-2020 Climate Normals put the average overnight low of its coldest month at 49.1°F. NOAA’s daily records show zero days at or below 32°F in 30 years, and the frost-free season is listed as 365 days. A freeze simply does not happen in an average year there, so the northern ritual of lifting, curing and boxing tubers has no job to do. (You can read the underlying NOAA station normals yourself.)
What matters instead is heat, drought and water restrictions. Mulch in these gardens holds moisture and keeps roots cooler; it is not insulation against cold. Without a frost to shut the plants down, you end the season yourself. Ease off irrigation as autumn goes on, let dahlia foliage decline, then cut it back. Cannas tend to keep growing, so remove tired stalks as they tatter. Gladiolus corms stay put and often multiply underground.
Where the line falls
Northern California, the Central Valley and the Sierra do freeze, and the Sierra freezes hardest. We can’t hand you a zone number as the cutoff, because the facts here don’t support one. A practical test works better. If your yard sees freezing nights in a normal winter, treat these three plants as lift-and-store. Mulch over a tuber buys a margin against a light frost. It does not save one from a deep freeze.
To see where your own garden stands, start with the First and Last Frost Dates in California and compare them against last winter’s coldest nights at your address. Hardy spring bulbs follow different rules entirely; Which Spring Bulbs Survive Your Winter covers that side of the question.
When to lift them
The signal is not a calendar date. It is a frost that turns dahlia, canna and gladiolus leaves black and limp. That blackening tells you the plant has stopped growing and is done sending energy down to its roots. The facts here carry no single first-frost date for the freezing parts of California, and any date we invented would be wrong for half the readers. The timing is relative: lift a short while after the first frost has blackened the foliage and the stems have collapsed, and before the ground freezes hard.
Reading your own frost
Direction matters. Higher elevations and spots farther north get their first fall frost earlier, so the lifting window opens earlier there too. Sierra gardens may be lifting while a valley-floor garden is still blooming. The same plant, the same job, a different week. Look at your local first fall frost and count forward from it.
On a dry day, cut the stalks back to a few inches above the soil. Push a garden fork in well away from the clump, since dahlia necks snap easily and a broken neck means a tuber that won’t sprout. Loosen the soil all the way around and lever the clump up gently. Cannas are tougher: lift the rhizome mass with soil attached, then shake it free. Gladiolus corms should be pulled when the leaves turn yellow-brown. They don’t need to wait for a killing frost, but in freeze country they must be out before the ground freezes.
In the frost-free south there is no frost to watch for. If you lift anyway, to divide a crowded clump or because winter-wet clay is rotting tubers in place, wait until the foliage has clearly declined and the plant has gone dormant.
Why lifting early backfires
Pulling tubers while the plant is still green feels responsible. It isn’t. A tuber lifted too soon has thin skin and has not finished filling with stored energy. It also carries more moisture, and moisture in a storage box is what feeds rot. A mature tuber, lifted after the foliage dies back, has firmer skin that cures properly and shrugs off the long winter.
Waiting too long has its own cost, but the frost-blackened foliage gives you a margin. The tubers sit insulated by soil for a short stretch after the first frost. Use that stretch to schedule the work for a dry day rather than rushing it in a soggy one. A wet dig makes for muddy tubers that are slow to cure. It is better to lose a couple of days to the weather than to store tubers that are still soaked.
Storing them over winter
Stored tubers need to be cured, lightly cleaned, then kept cool, dark and slightly moist so they neither rot nor shrivel. Skip any one of those and the box turns into a compost bin by midwinter.
Cure and clean, lightly
Set the lifted clumps in a sheltered, airy spot out of sun and rain, such as a covered porch or a garage, and leave them for a few days. The surface should dry and the skin firm up. Then brush off the loose soil. Scrubbing is a mistake, because it scars the skin. If you do rinse, dry the tubers completely before they go in a box. Cut away anything soft or damaged, and label each clump by variety now, while you still remember which is which.
Three plants, three storage styles
Dahlias and cannas want a little moisture around them. Gladiolus corms want to be dry. Mixing them in one box is the usual way people lose one of the three.
| Plant | What you store | Packing | Moisture | Warning sign |
|---|---|---|---|---|
| Dahlia | Tuber clump with fragile necks | Boxes with barely damp wood shavings, peat or vermiculite | Slightly moist | Wrinkled skin means too dry; soft spots mean too wet |
| Canna | Rhizome mass, tougher than dahlia | Similar packing, kept from drying out entirely | Slightly moist | Shriveling rhizomes; mold at cut ends |
| Gladiolus | Corms, old base removed after curing | Mesh or paper bags, airy, no damp medium | Dry | Soft, moldy or hollow corms |
Keep every box cool and dark, but never frozen. Inland California garages can run warm even in winter, and warmth is how dahlia tubers shrivel. A closet against an inside wall or a shaded, unheated room is often the better spot than a sun-exposed garage.
The monthly check
Storage is not a set-and-forget job. Open every box once a month all winter. A tuber that has started to soften goes in the trash before it passes the rot along. One that has begun to wrinkle gets a light mist or a slightly damper packing medium. Mold on gladiolus corms means the air is too still and damp, so open the bags and let them breathe. Ten minutes a month is the difference between a full box in spring and a box of mush.
Empty beds in fall are also the time to think about what replaces these plants. Hardy spring bulbs (more under Spring Bulbs) can go in as the summer tubers come out, and Planting Spring Bulbs in California sorts out what suits each part of the state.
What goes wrong
Rot is the most common failure, and it comes in two forms. In storage, it shows up as soft, dark, sometimes sour-smelling spots on tubers that were packed wet or lifted before they matured. In the ground, it happens in frost-free gardens where winter-wet clay never drains, and tubers turn to mush without ever feeling a freeze. The fix is the same: cure thoroughly before boxing, and plant in soil that drains.
Shriveling is the opposite problem. Tubers go wrinkled and light, like dried fruit, because the storage space is too warm or too dry. A tuber that is only wrinkled can still be saved with slightly damper packing and a cooler spot. One that has gone hollow and papery cannot.
Lifting too early, as covered above, gives you immature tubers that rot or fail to sprout. The cure is patience. Wait for the frost-blackened foliage and a collapsed stem.
The last mistake is geographic: leaving tubers in the ground one zone too far north. A gardener in a freezing part of the state sees a neighbor on the coast leaving dahlias in the ground and copies the habit. After a hard freeze, the tubers come up translucent, mushy or blackened. Don’t rely on mulch to cover the gap. If your yard sees freezing nights in a normal winter, lift. Los Angeles’s frost-free record does not travel to the Central Valley or the Sierra.
Common questions
Do I need to dig up dahlias in Los Angeles?
No. Los Angeles has had no days at or below 32°F in 30 years of NOAA daily records, so the tubers can stay in the ground under mulch. Lifting is optional there, for instance to divide a clump that has grown crowded or to move it to better-draining soil. For other fall chores in your region, browse the California guides.
Can I leave cannas and gladiolus in the ground in the Central Valley?
The Central Valley does freeze, so treat it as lifting territory unless your own yard rarely sees a hard freeze. Mulch over cannas can carry them through a light frost, but a deep freeze is a gamble, and a lost rhizome is a lost plant. Gladiolus corms are less forgiving still. If you want to test the odds, leave a few and lift the rest.
What if frost never blackens my foliage but the plants look tired?
Then the plants are telling you the season is over even though the weather isn’t. Ease off watering, let the foliage decline, and cut the stalks back. In a frost-free garden, that is your signal to leave the tubers in place or lift them if you want to divide.
Should I wash the tubers before storing them?
Brush off loose soil rather than scrubbing. If you rinse, dry the tubers completely before packing. For gladiolus, cure the corms until dry, then snap off the shriveled old corm at the base. The plump new corm sitting on top is the one you keep, and the tiny cormels around it can be saved too, though they take longer to bloom.