In short: Lift dahlia tubers once the first frost has blackened the foliage (usually between late September and November in the UK), cut the stems back to about 10–15 cm, dry the clumps upside down for a couple of weeks, then pack them in trays of coco coir with the old stems exposed and keep them somewhere cool, dark and frost-free until March. Coir does the job the RHS gives to dry sand, soil or compost — and it is lighter, cleaner and reusable in spring for potting the tubers up. The same method stores cannas, tuberous begonias and gladioli. One 5 kg brick makes about 75 litres, enough to bed down 50 or more clumps.
Why lift dahlias at all?
Dahlia tubers are only borderline hardy. In mild, well-drained gardens many people now leave them in the ground under a thick mulch, and the RHS accepts that as an option. But on clay, in cold areas, or with a variety you cannot replace, lifting is the safer bet: a tuber that sits wet and frozen rots, and you will not know until nothing comes up in May. Storage is about two things — keeping frost off, and keeping the tubers neither so wet that they rot nor so dry that they shrivel to nothing.
What to store them in — and where coco coir fits
The RHS method is to bury the dried clumps in trays filled with dry sand, soil or compost, leaving only the old flower stalks exposed, and for cannas it names trays of sand, coir or vermiculite. All of these are doing the same job: holding the tubers in a dark, insulating, slightly humid cushion that stops them drying out while letting any surplus moisture escape. Coco coir is the peat-free version of that cushion:
| Storage medium | Pros | Cons |
|---|---|---|
| Coco coir | Light, clean, holds a little humidity so tubers do not shrivel, easy to dry to exactly the dampness you want, reusable for potting up in spring | Needs expanding first; must be dried back to barely damp before use |
| Dry sand | Cheap, inert | Heavy, can dry tubers out, no use afterwards |
| Old compost | Free if you have it | Variable moisture, may carry rot organisms from last season |
| Vermiculite | Very light, holds humidity well | Expensive in quantity, dusty |
| Newspaper only | Free | No insulation, tubers shrivel by February |
Getting the coir to the right dampness
This is the one thing to get right. Freshly expanded coir is far too wet for storage. Expand the brick (20 litres of water, 20–30 minutes), then spread it out on a tarpaulin or in shallow trays in the shed for a few days until it is barely damp — a squeezed handful should not release any water and should fall apart when you open your hand. If in doubt, drier is safer than wetter: you can always mist the trays lightly in January if the tubers start to shrivel, but you cannot un-rot a tuber.
How to lift and store dahlia tubers, step by step
- Wait for the first frost to blacken the leaves, or lift in November anyway if frost has not come. Cut the stems to 10–15 cm.
- Lift carefully with a fork, working well out from the stem — the tubers spread wider than you think and snap easily.
- Shake and rinse off the soil, and label each clump with a tag through the stem. You will not remember the variety in March.
- Dry upside down for one to three weeks somewhere frost-free and airy, so that any water in the hollow stems drains out. Stem rot is the main cause of lost tubers.
- Inspect and cut away anything soft or damaged back to clean tissue.
- Pack in coir. Put 3–4 cm of barely damp coir in a seed tray or crate, sit the clumps on it, and fill around them so only the cut stems show.
- Store cool, dark and frost-free — a garage, shed or unheated spare room, ideally somewhere that stays a few degrees above freezing and never warms up enough to start growth.
- Check monthly. Remove anything rotting. If the tubers look wrinkled, mist the coir lightly. If the coir feels wet, tip it out and replace with drier coir.
How much coco coir do you need?
| What you are storing | Coir needed | One 5 kg brick (≈75 L) covers |
|---|---|---|
| One average dahlia clump | ≈ 1–1.5 L | 50–70 clumps |
| A standard 35 × 22 cm seed tray, 5 cm deep | ≈ 4 L | ≈ 18 trays |
| A 60 L crate of cannas | ≈ 20 L | 3–4 crates |
The same method for cannas, begonias and gladioli
- Cannas — lift after frost, keep a little soil on the rhizomes, dry briefly and pack in barely damp coir. The RHS lists coir as a storage medium for cannas. Keep just frost-free; they shrivel if kept bone dry.
- Tuberous begonias — let the stems die back, lift, dry, then store the tubers hollow-side up in dry coir, cool and dark.
- Gladioli corms — dry thoroughly, break off the old corm, and store in coir or paper bags somewhere cool and airy; they prefer drier conditions than dahlias.
- Root vegetables — carrots and beetroot for winter use store well in boxes of damp coir in a cold shed, the traditional sand-box method without the weight.
Waking them up in spring
In March or early April, pot the clumps into a mix of coir and peat-free compost, water once and put them somewhere light at around 15 °C. Shoots appear in a few weeks; you can take basal cuttings when they are 8–10 cm tall, and plant the tubers out after the last frost. The storage coir goes straight into the potting mix, so nothing is wasted. How to make a coir potting mix.
Frequently asked questions
Should dahlia tubers be stored damp or dry?
Barely damp. Bone-dry storage shrivels them; wet storage rots them. Coir that is just moist to the touch, in a cool place, holds the balance — check monthly and adjust.
Can I store dahlias in coco coir?
Yes. Use expanded coir dried back to barely damp, pack the clumps in with the stems exposed, and keep them cool, dark and frost-free. The RHS lists coir among the storage media for cannas, and the method is identical for dahlias.
What temperature should dahlia tubers be stored at?
Cool and frost-free — a garage or shed that stays above freezing but well below room temperature. Warmth starts them into growth early; frost kills them.
Do I have to lift dahlias in the UK?
Not always. In mild areas with free-draining soil, a thick dry mulch over the crown often gets them through. On clay, in frost pockets, or for varieties you value, lifting is safer.
How do I stop stored tubers rotting?
Dry them upside down before storing so water drains from the stems, cut out damaged tissue, keep the coir barely damp rather than wet, and check monthly.
Is coco peat the same as coco coir?
Yes — coco peat and coco coir are the same material.
Washed, calcium-buffered coco coir — 75 litres per 5 kg brick, peat-free, free UK delivery. Store the tubers in it now, pot them up in it in spring.
Shop the 5 kg brick → Coir as peat-free bulb fibre