Dig them up. In Newfoundland and Labrador, dahlia tubers, canna rhizomes and gladiolus corms come out of the ground after the first hard frost blackens the foliage, which on average arrives around October 17 in St. John’s. Lift in the week or two after that frost, so late October into early November in the capital region, and earlier in the colder north and uplands. Leaving them in the ground is a gamble most gardeners here lose.
Do you have to dig them up in Newfoundland and Labrador?
Yes, and the numbers explain why. Natural Resources Canada places St. John’s in Canadian hardiness zone 6a, based on its 1991-2020 normals. Environment and Climate Change Canada (ECCC) puts the mean daily minimum of the coldest month there at -8.7 °C (16.4 °F), from its 1981-2010 normals. Those are the nights that decide what survives, and they sit far below what a dahlia tuber tolerates once the ground cools through. The honest answer for this territory is to lift all three every fall and keep them somewhere frost-free until spring.
Why a Canadian zone number is not a green light
Zone 6a is a Canadian zone, and it is not a USDA zone. Natural Resources Canada says outright that there is no simple conversion between the two systems. The Canadian one blends seven climate variables, while the USDA one uses a single winter-minimum figure. NRCan’s own example makes the point: Canadian zone 4a overlaps nine different USDA zones, from 3a to 7a. So a US catalog that calls a dahlia “winter hardy in zone 7 or 8” tells you very little about a St. John’s backyard, and a Canadian 6a on a plant tag does not tell you the tubers will make it through a Newfoundland winter either.
Dahlias, cannas and gladiolus are all tender. Their storage organs hold a lot of water, and when that water freezes the tissue turns to mush as it thaws. Mulch slows the cooling of the soil. It does not stop it across a winter where the coldest month’s nights average -8.7 °C, with plenty of nights colder still. Hardy bulbs like tulips and daffodils are built for that cold, which is why the Spring Bulbs that go in each fall stay put while these three come out.
Where the line falls inside the province
The zone and the temperature above belong to the St. John’s reference city, not to the whole province, and the first-frost date comes from the St. John’s A weather station. Newfoundland and Labrador is not one climate. Farther north, at higher elevation and inland, winter arrives sooner and the first fall frost comes earlier than it does on the Avalon Peninsula coast. That does not change the verdict, it tightens the schedule: where it is colder, the tubers come out earlier, not later. Nothing in the figures for this territory points to a place where leaving them in the ground becomes safe. For other bulb questions across the province, the Newfoundland and Labrador guides cover the wider picture.
When to lift them
The signal is not a date on the calendar. It is a frost cold enough to blacken the foliage of the dahlias and cannas, and gladiolus tops that have yellowed and browned. Once that happens, the plant has stopped sending energy to the storage organ, and the clock starts. Lift within about a week or two of the blackening frost, choosing a dry day when the soil is not sodden.
Reading the St. John’s frost figure
ECCC’s 1981-2010 normals for the St. John’s A station give an average first fall frost of October 17. Treat that as the midpoint of a window, not a safe date. An average means that in about one year out of two, the frost comes later than October 17, and in the other half it comes earlier. Counting forward a week or two from that midpoint puts a typical lifting window in the second half of October, running into early November in years when frost holds off. In a colder or higher district, the same logic applies but the whole window slides earlier, because the first frost lands earlier. The figure also comes from 1981-2010 normals, not the 1991-2020 period used for US figures, so do not line the two up as if they were the same yardstick. A deeper look at local dates is in First and Last Frost Dates in Newfoundland and Labrador.
A single light frost that only nips the leaf edges does not count. Wait for the foliage to collapse and darken. If an early frost is forecast while the plants are still green and you want a few more weeks of flowers, a sheet or frost cloth over the plants for the night can buy time. Once the blackening frost arrives, stop waiting.
Why lifting early backfires
The temptation is to dig the moment the weather turns raw, before the plants look finished. Tubers pulled while the plant is still green have thin skins and high water content, and they have not finished maturing. They look fine on the day, then rot in storage, often from the neck where the stem was cut. The week or two after frost is when the skins toughen and the tissue firms up, which is exactly what gets them through months in a box.
The reverse risk is waiting too long. A second, harder frost or a stretch of cold, wet soil can reach the tubers and set rot in motion. The target is the gap between the blackening frost and the deep freeze, and in Newfoundland and Labrador that gap is real but not generous.
When you dig, work a garden fork well out from the clump and lift gently, because a snapped neck on a dahlia tuber is a tuber that will not sprout. Cut the stems down to a short stub. Gladiolus come out with the foliage trimmed close to the corm. Shake off loose soil but do not wash or scrub at this stage.
Storing them over winter
Lifting is half the job. The sequence is cure, clean lightly, then store cool, dark and slightly moist, so the tubers neither rot nor shrivel. Curing means letting the surface dry in a sheltered, airy place out of rain and out of direct sun, until the skin feels dry and the cut ends have sealed over. It does not mean baking them. Brush off dry soil by hand. Hold off on heavy washing, since wet skin invites rot, and leave the thin skin alone.
The storage spot has to stay frost-free all winter. With the coldest month’s nights averaging -8.7 °C in St. John’s, an unheated garage or shed can freeze solid, so a cool basement, a closet against an interior wall or a cold room that stays above freezing is a safer bet. Darkness matters too, because light and warmth wake the tubers early.
The three do not want the same thing
Dahlia tubers and canna rhizomes are fleshy and can dry out, so they are packed in a barely damp, loose material such as peat, sawdust or vermiculite. Gladiolus corms are different. They want to stay dry and ventilated, because a damp corm molds quickly. Here is how the three compare:
| Plant | What you store | Curing | Packing | Moisture |
|---|---|---|---|---|
| Dahlias | Clumps of tubers with a bit of stem | Dry the surface, then trim | Box or crate with barely damp, loose material | Slightly moist; shrivel if too dry, rot if wet |
| Cannas | Fleshy rhizomes, foliage cut back | Dry the surface in an airy spot | Boxes or paper bags with lightly damp material | Slightly moist; fleshy rhizomes dry out easily |
| Gladiolus | Corms, with the old shriveled corm and small cormlets removed after drying | Longer and drier than the others | Mesh bags, paper bags or open trays | Dry and well ventilated |
Keep each variety labeled, because by February a box of unmarked dahlias is a guessing game, and the colors you planned in the border will not be what you get.
The monthly check that saves them
Set a reminder and check every box once a month through winter. Pick the tubers up and look at them. Soft spots, a sour smell or fuzzy mold mean rot, and a rotten piece will spread it to its neighbors if left alone. Cut away the bad part with a clean knife, let the cut dry, and repack the rest in fresher material. Wrinkled, rubbery skin means the opposite problem, so add a light mist to the packing material, never straight onto the tubers. Gladiolus corms get the same look-over, with a different fix: if they feel clammy, spread them out to dry again. A few minutes a month is the whole difference between a healthy stock in spring and a box of mush.
What goes wrong
Most losses come down to four problems, and each leaves a clear sign if you know where to look. Almost all of them trace back to water, either too much or too little, or to timing.
Problems in storage
Rot shows up as soft, brown or gray patches, a sour or musty smell, and sometimes white or gray mold. It comes from tubers stored wet, packed in sealed plastic, lifted before they matured, or kept somewhere too warm. Prevent it by curing properly, using only barely damp packing material, giving air some way in, and catching it at the monthly check. Shriveling is the opposite: tubers that feel wrinkled, light and rubbery. The cause is air that is too dry or too warm, or packing that has dried out entirely. A light mist on the material and a cooler spot usually bring them back unless they have collapsed completely. A shriveled gladiolus corm, though, is a lost cause if it has turned papery.
Problems in the ground and at lifting
Lifting too early gives soft tubers that rot in storage, even when the storage conditions are perfect. The fix is patience: wait for the blackening frost, then dig within the week or two that follows. The other mistake is leaving them in the ground, trusting a hardiness rating from a US source. Come spring, the tubers are mush or simply gone, and the first sign is a bed where nothing emerges. Because the Canadian system does not convert to USDA zones, lift every fall regardless of what a US zone rating says. Hardy bulbs are another matter, and Which Spring Bulbs Survive Your Winter sorts out which ones can stay. For the fall-planted kind, Planting Spring Bulbs in Newfoundland and Labrador has the timing.
Common questions
Can I leave dahlias in the ground under heavy mulch in St. John’s?
It is not worth the risk. The coldest month’s nights in St. John’s average -8.7 °C, according to ECCC’s 1981-2010 normals, and mulch only slows how fast the soil cools. Tubers that freeze turn soft and rot. Lifting costs an afternoon, and replacing a collection of dahlias costs far more.
Should I dig before the first frost to be safe?
No. Digging while the plants are still green gives immature tubers with thin skin that tend to rot in storage. If a frost is forecast and you want to protect the plants, cover them for the night and wait for the frost that actually blackens the foliage. Then lift within about a week or two.
How often should I check stored tubers?
Once a month. Look for soft spots, mold or sour smells, which mean rot, and for wrinkled, rubbery skin, which means they are drying out. Remove rot with a clean knife and let the cut surface dry before repacking.
When do I plant them back out?
After the last spring frost has passed, since all three are tender. That date comes later in the colder north and at higher elevations, the mirror image of the fall frost arriving earlier there. The St. John’s figures come from ECCC’s 1981-2010 normals and the zone from Natural Resources Canada’s 1991-2020 data, so inland and northern gardeners should treat any St. John’s date as a starting point and adjust later in spring and earlier in fall.