Dahlia tubers

Dahlia tubers can be started in pots indoors or in a frost-free greenhouse from March or early April, giving them a head start before summer. They can also be planted directly into the ground from around mid to late April, but emerging shoots must be protected from frost. Plants started under cover should only be moved permanently outside once the risk of frost has passed, often from late May onwards in much of the UK.

Position the tuber horizontally with the old stem or crown facing upwards, where the new shoots will emerge. When starting dahlias in pots, cover the crown with only a shallow layer of peat-free compost and keep them somewhere bright and frost-free. Water sparingly at first, increasing the amount once leafy shoots are actively growing.

The cluster of long, fleshy tubers should sit below the crown, with the old stem and growing points uppermost. New shoots emerge from the crown rather than from the ends of the individual tubers. If the tuber looks confusing, use the remains of last year's stem as your guide to the top.

Dahlias usually begin flowering in summer and continue through autumn until the first frosts, with exact timing depending on the variety and how early the tubers were started. Plants started under cover in spring generally flower earlier than tubers planted directly into the garden.

Pinching is not essential, but it is a useful way to encourage bushier plants with more flowering stems. Once a young dahlia has developed several pairs of leaves, remove the central growing tip just above a pair of leaves. The plant will then branch from lower down rather than continuing as one dominant stem. RHS

Deadhead regularly and keep picking flowers for the vase. Removing spent blooms prevents the plant from putting energy into seed and encourages it to continue producing new buds. With regular deadheading, healthy dahlias can keep flowering well into autumn until frost finally brings the display to an end.

You can in some milder, well-drained UK gardens, but there is always a risk from severe frost or prolonged winter wet. If leaving tubers in place, cut back the frost-damaged stems and cover the crown with a generous insulating mulch. In colder gardens or heavy, wet soil, lifting the tubers is the safer option.

After the first frost has blackened the foliage, lift the tubers carefully and remove most of the soil. Allow them to dry before storing them somewhere cool, dark, dry and frost-free for winter. Check stored tubers occasionally and discard any that develop significant rot before starting the healthy ones back into growth in spring.

Yes. Dahlias can make excellent container plants, particularly compact and medium-sized varieties. Choose a generous pot with good drainage and use peat-free multipurpose compost. Container-grown dahlias need more regular watering than plants in the ground and may benefit from a potassium-rich feed once flowering begins.