Ali, the safest method is to **lift the tubers, dry them off and store them somewhere cool and frost-free**, especially if your soil stays wet in winter. ([rhs.org.uk](https://www.rhs.org.uk/plants/dahlia/growing-guide)) ### Step by step 1. **Wait until frost blackens the foliage.** Then cut the stems back to about **10–15cm (4–6in)**. If you’re gardening in the UK and frost is late, lift them by late November. ([rhs.org.uk](https://www.rhs.org.uk/plants/dahlia/growing-guide)) 2. **Lift carefully with a garden fork.** Work around the clump, avoiding the fleshy tubers, and gently remove loose soil. Label each clump with its variety or flower colour. ([rhs.org.uk](https://www.rhs.org.uk/prevention-protection/overwintering-tender-plants-lifting-or-mulching?adlt=strict&toWww=1)) 3. **Dry them upside down under cover**, somewhere cool and frost-free, so moisture drains from the hollow stems. Allow a couple of weeks, checking that they are dry before packing. Leave healthy clumps intact; dividing is best left until spring. ([rhs.org.uk](https://www.rhs.org.uk/plants/dahlia/growing-guide)) 4. **Pack into an open-topped box or crate.** Surround the tubers with dry spent potting compost or dry sand, leaving the cut stalks exposed. Store somewhere dark, cool and reliably frost-free—a garage or shed is suitable only if it doesn’t freeze inside. ([rhs.org.uk](https://www.rhs.org.uk/plants/dahlia/growing-guide)) 5. **Check regularly through winter.** I suggest a monthly check: remove any tubers showing rot before it spreads. ([rhs.org.uk](https://www.rhs.org.uk/plants/dahlia/growing-guide)) In a mild, sheltered UK garden with free-draining soil, you can instead leave them in the ground beneath **15cm (6in) of mulch**, but a very wet or severe winter can still cause losses. ([rhs.org.uk](https://www.rhs.org.uk/plants/dahlia/growing-guide))