Dahlias are frost-tender tuberous plants that can overwinter if the weather is mild. However, a severe winter can can result in losses, so many gardeners prefer to lift their tubers, but are unsure how to keep them.
When to lift dahlias
Once frost has blackened the dahlia, cut down the stems to four to six inches (up to 15cm) and then lift the tubers - making sure that they are labelled.
How to store tubers
Dry the dahlia tubers off by upending the tubers, so the stems face downwards, for at least two weeks in a dry frost-free place.
Once the tubers look and feel dry, shake off any remaining soil and place them into containers of dry, peaty compost so the stems stick out above the compost.
Store in a frost-free place. Polystyrene fish boxes are excellent, or use plastic trays used for delivering bread etc.
Keep the tubers dry and cool, but frost-free.
Getting dahlia tubers ready for planting
Begin to water them, still in their boxes, from mid-March onwards.
They will need a warm, light position and a frost-free greenhouse is ideal.
Grow them on and then pot them on when the shoots are three inches high.
Pinch out the shoots when they are six inches tall, to produce bushier plants.
Read our guide to growing dahlias
What to do with dahlias in spring
Your dahlias will only begin to grow again in warmth so they must be kept as warm as possible. The slightest hint of frost will check their growth and blacken their foliage. Use thick fleece on cold nights.
Do not plant outside until the first week of June. Harden them off for at least a week before planting, by placing them somewhere sheltered outside. This toughens the foliage, deterring slugs.
Stake as you plant. Use three canes, about one metre in height, and create an equilateral triangle. Cap them with protective tops and then tie two separate lines of string round the canes - one higher than the other.
Water well in the first half of summer so that your plants establish themselves.
Feed with a potash-rich plant food, either home-made comfrey tea or liquid tomato feed, once buds appear.
Once flowering, deadhead every few days.
The pointed seed heads (which feel soggy to the touch) can look very similar to the bun-shaped buds when you’re a novice. So get your eye in before you start.
Taking dahlia cuttings
Look for new shoots reach about three inches in length (75mm). Fill three-inch plastic pots with John Innes no 1 and water them with a fine rose.
Using a sharp knife, cut away the shoot just above the base where they join the crown. Do not damage the crown. Discard any hollow-stemmed cuttings.
Trim the cutting just below the lowest pair of leaves and remove the leaves carefully. Dampen the end of the cutting and dip into hormone rooting powder. Insert the cutting into the pot, making a hole with a dibber, and firm with your fingers. Label them. One pot can house several cuttings from the same variety.
Place in a warm propagator if possible, away from direct sunlight. Cuttings should root within twenty days.
Once new leaves appear pot them up individually into John Innes 2. Stop your young plant once only, by pinching out the growing tip. This will make plants bushier.
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