Dormancy And Winter Treatment In Gardening Approaches
Where they are grown in border setting tender summer flowering plants, such as dahlias, begonias, cannas and gladioli should be lifted in autumn and brought into growth again in spring if they are to flower once more in the summer. The tubers and corms of these plants should be lifted, dried and stored in dry, cool, frost free conditions.
Begonias and gladioli are stored dry, dahlias and cannas should be stored in barely moist peat or coarse vermiculite. Most bulbs and tubers should be lifted before the first frosts. Dahlias, however, will benefit if the foliage is actually killed by frost. When this happens, the leaves become blackened. If your dahlias have stopped flowering but there have still been no autumn frosts, lift them anyway.
In some mild areas it is possible to cut off the dahlia foliage and leave the tubers in the ground, protecting them with a mulch of grit with a layer of leaf mould or bark chipping, in the same way that nerines, crinums and the hardier types of agapanthus are left in the ground. Dahlias treated in this way are always at risk, especially if the winter happens to be severe.
When green shoots begin to emerge on lifted dahlias in spring, water sparingly to keep the compost moist. Then in late spring or early summer, after all risk of frost has passed, choose a sunny, sheltered spot and prepare a planting hole. Cannas should be treated in the same way as dahlias, except that the stalks of cannas are not hollow and it is not necessary to hang them upside down to drain.
Moreover, cannas produces rhizomes, not tubers, and these are easily separated in spring when the new shoots start to emerge to produce new plants.