Dormancy in Cold Hardy Tropical Plants
From TejasTropicals Articles
There are a large number of tropical plants that can tolerate considerable cold. How is it that some tropicals die at temps below 32F degrees and others can be grown in zone 8, some even in zone 7?
It has to do with dormancy as opposed to evergreen continuously growing tropicals. Dormancy in tropical plants usually occurs in tropical regions that experience monsoonal and then dry seasons. During the dry season the plants are stressed and shutdown. This usually takes place at the same time as our winter. Cold temps stress the plants similar to drought and so they go dormant.
These areas include parts of Africa and Asia but the epicenter for these plants are in India,northern SE Asia, and China. There are two groups of plants from this region that include a large number of species that go dormant; these are the Gingers and Aroids. Within the Gingers the dormant genera include Curcuma, Globba, Hedychium, Kaempferia, and many of the Zingibers. Of the Aroids the most dramatic genera are the Amorphophallus and Elephant Ears or Colocasias.
Since dormancy is caused by dry conditions in these plants, in habitat, we need to take this into account in cultivation. Most areas of the US in zone 7-8 and warmer experience wet winters. Since these plants go dormant during a dry season they require dry conditions during our winters to prevent root or rhizome rot. This can be accomplished in several ways.
They can be planted in well drained or raised beds. They can be grown in containers that are stored dry for the winter. Lastly, the rhizomes or tubers can be dug up after the first hard frost and stored in semi dry bark mulch in a garage or basement similar to storing spring bulbs, such as tulips, for the winter. The picture demonstrates how we utilize rubber tubs with composted pinebark to store our rhizomes and tubers. They are uncovered for demonstration and will be completely covered and kept barely moist until spring. We utilize all three of these methods successfully.
Buying dormant rhizomes have many advantages. Shipping costs are greatly reduced since you are only buying the growing point of the plant. The size of the plant can be considerably larger, especially compared to small tissue culture plants which have become the norm with online nurseries of late. The rhizomes we sell are from mature plants so they will attain a much larger plant size during the growing season. You don’t have to plant the rhizome right away or care for it until planted in the spring. With all these advantages why not give them a try in your garden this year.