overwinter dahlias

Overwinter Dahlias

If you want to see those fat pom-pom dahlia blooms the size of a soup plate in your garden again next year, you have to care for the dormancy period of dahlia tubers. You can overwinter dahlias in two ways:

Leave them in the ground

Just leaving them to go to sleep where they grew is fine in temperate climates with no or light frost, as long as the soil is not constantly wet or cold, or of heavy clay.

Do this:

  • Cut the stems back to ground level.
  • Mark the spots where the tubers are with bamboo sticks and labels to remind you of their whereabouts.
  • Mulch the soil’s surface thickly with leaf mould, bark or compost.

Lift and store

You can overwinter dahlias by lifting the bulbs and storing them. This is recommended for very cold climates with heavy frost. Even though the tubers are underground, freezing soil temperatures will kill them off.

Do this:

  • Wait until after the first frost, which will damage the last bits of top growth, before cutting the stems back to just a few centimetres above ground level.
  • Use a fork to gently loosen the soil around the plants, taking care not to pierce the tubers, and lift them out.
  • Knock off as much of the soil as you can and gently wash the remainder off with your hosepipe.
  • To protect them against rot, dip the tubers in a fungicide – use Efekto’s Virikop or Kumulus WG.
  • Turn the tubers upside down on thick layers of newspaper so that the remaining stems are facing downwards, allowing all moisture and remaining sap to drain away. The tubers might take as long as two weeks to dry out completely in a dry, cool and shady place.
  • Store the tubers in flat boxes, brown paper bags or wooden crates in a dry, well-ventilated place like a garden shed or garage.
  • Use packing material like dry potting soil, pet bedding, perlite or vermiculite in layers between the tubers.
  • If the packing material is very dry, moisten it very lightly.
  • Inspect your tubers monthly for rot, and if you see any signs of rotting, discard them, as it will spread to others. If they look very shrivelled and dry you can very lightly moisten again.
  • Plant the tubers once more in late spring when all danger of frost is over.

Caution! Tools like secateurs, which you will be using to cut the old stems back, must be sterilised thoroughly all the time. Dip them in a mix of 1 part bleach and 10 parts of water to do so.

The Gardener