OVERWINTERING CANNAS
Cannas are not generally regarded as hardy, and the first frost of autumn will turn the leaves to mush. Cannas can be left in the ground in mild areas, where winters suffer few frosts, and if the rhizomes are well below the soil surface, or mulched with compost or bark as soon as the weather gets cold, the plants can survive outside in all but the coldest areas. It is a risk, however, and has a disadvantage in that the plants will not come into leaf until very late in spring, and do not always manage to produce flowers before the cold weather of late autumn prevents more growth. If they have to be left in the ground, it is best to cover clumps, once the foliage has been frosted, with a loose mulch of straw or bark chips, being sure to protect the new shoots from slugs in spring. It is better to lift the plants, either before or just after the first frost, and keep them in a frost-free place. They can then be dried off or kept slightly moist over winter. If dried, so that all foliage withers, the rhizomes can be stored in dry compost in a shed. The disadvantage is that not all the rhizomes will sprout, and it will take longer to grow a large plant than if the rhizomes had been kept moist in a light place, at a temperature of 5°C or more. If kept ‘ticking over’, the foliage is cut back in autumn and the rhizomes kept in boxes of compost, and watered just enough to keep the plants alive. In early March, the plants can be divided, potting the divisions and starting them into growth at a temperature of 10°C or higher, if possible. Cannas grown in containers are more prone to frost damage, so must not be left outside over winter.