In Ireland’s cool, damp winters, the safest approach is to lift and store dahlias (tubers) and cannas (rhizomes) once foliage is blackened by the first frost or by early–mid November at the latest. Plants in pots are more vulnerable to cold and waterlogging, so prioritise lifting those first. A frost-free greenhouse is an excellent place to overwinter clean, dry tubers/rhizomes.
Quick check: can I lift now?
- Pots: Yes—lift now. Pots are at high risk from cold and persistent rain.
- In-ground plants: Lift after the first frost blackens foliage or by early–mid November in most areas.
- Soil too wet to work? Cut stems back, lay a temporary mulch, and lift as soon as workable.
How to lift & store Dahlia tubers
- Cut back stems to 10–15 cm.
- Lift gently with a fork, keeping clumps intact; avoid stabbing the tubers.
- Dry in a cool, airy, frost-free place for ~7 days. Brush off loose soil.
- Pack in boxes or crates with barely-moist peat-free compost, wood shavings, or perlite. Keep the crown just above the medium. Add labels.
- Store dark and frost-free at roughly 4–8 °C. Check monthly:
- If shrivelling: lightly mist the packing medium (not the tubers directly).
- If rot appears: cut back to sound tissue and dust the cut with sulphur or ground cinnamon.
- Divide in late winter/early spring when growth “eyes” are visible; each division needs a piece of crown with at least one eye.
How to lift & store Cannas (Canna rhizomes)
- Cut back stems to 10–15 cm and lift clumps.
- Clean & dry for 2–5 days somewhere airy and frost-free.
- Store slightly drier than dahlias: either wrapped in dry paper, in perlite, or in barely-moist compost.
- Temperature: aim for 5–10 °C, dark and frost-free. Check monthly for rot or severe shrivelling.
- Divide in spring, each piece with 2–3 eyes. Pot up indoors for a head start.
Using a frost-free greenhouse
- Bench, not floor: keep boxes off the ground (bench or pallet) to avoid cold/damp pockets.
- Vent on mild, dry days to reduce condensation; good airflow prevents mould.
- Keep it dark to avoid premature sprouting—store under benches or cover crates with card/newspaper.
- Have fleece ready as a backup for rare cold snaps or power cuts.
- Pots vs. bare storage: empty wet pots; store cleaned tubers/rhizomes in crates or boxes instead of leaving them planted.
Troubleshooting
- Rotting tubers/rhizomes: remove affected parts, dust cuts, and increase airflow. Check that your medium isn’t wet.
- Shrivelling: mist the storage medium lightly and reduce ventilation on very windy/dry spells.
- Mice: use mesh lids on crates and set traps; mice love dahlia tubers.
- Mould on stems: harmless on the cut stem; trim back to clean tissue and discard the rest.
Re-starting in spring
From late February to March, pot up divisions in peat-free compost indoors or under cover. Grow on with good light, minimal watering, and plant out after the last frost risk for your area. Harden off for 7–10 days before planting outside.
