I have had a few questions about getting the tropical garden ready for winter. Specifically: What do I do with my tropicals when I donít live in a tropical climate? More to the point: Do I have to drag this plant inside in the winter?
Certainly these questions need to be addressed before one acquires tropical plants because each plant has its own requirements. Some plants will be more sensitive than others when it comes to the changing environment winter brings, and others may not be so demanding.
Many of the tropical plants I keep have to be greenhoused. I have a few which exhibit damage at 50į F.
However, many rhizomatous and bulbous plants found in tropical monsoonal Asia do very well when subjected to seasonal cold. A seasonal lack of moisture in their native habitat forces them into a conservative mode where they either donít need as much nutrition or they go completely dormant when rain is scarce. When the rains return, the plants wake up to take advantage of the ready availability of moisture and nutrients and continue their growth cycle. For many tropical plants we can take advantage of this growth and rest cycle by mimicking these conditions and timing them to coincide with our warm and cold seasons.
Many gingers and aroids readily adapt to the monsoonal/seasonal overlay we impose on them and grow in the spring and summer months and go dormant in the fall and winter. Gingers such as curcumas, some hedychiae and some zingibers and a few costaceae will adapt to more temperate regions as will some aroids like a few alocasias and colocasias.
The best way to mimic this monsoonal cycle of dormancy and renaissance outdoors is accomplished through preparation. In coastal Texas, we are subject to wet winter conditions. Wet is the last thing many tropicals want to be in the cold season. If we are to successfully mimic the monsoon, the plants must be as dry as we can make them in the winter. Short of digging them up, which everyone wants to avoid, the standard gardening method of raised beds with high quality well draining soil is the answer.
Too much moisture in winter for hardy tropicals will cause rot. A raised bed with well draining soil ensures that water will quickly run through the bed and not stand around the plant. Plants that exhibit this behavior of dormancy and growth are called deciduous plants. Not all tropicals are deciduous.
What about non-hardy and non-deciduous tropicals? There are methods to keeping non-hardy tropicals outdoors in temperate regions. Pretty much, there is no getting around the fact that if your tropical plant freezes, it will die. You must supply heat to the plant and, on one hand, what many casual gardeners donít want to do is spend time and resources in providing that environment for thier tropical plant. On the other hand, many gardeners want to buy that Zone 10 or 11 tropical plant and keep it outside and yet have it survive the winter.
As mentioned above, a well drained, raised bed is essential but not enough. The method that works for me in zone 9 Houston, takes advantage of the natural heat sink created by my house.
As the winter day progresses, my house both absorbs some heat from the sun and reflects some. When the sun goes down my house gives off heat. It comes from the residual heat absorbed earlier in the day and from inefficiency of my heating system. The extra heat is just enough to maintain a few tropicals immediately next to your house over the winter. This method generally works to keep a plant rated for a zone higher than what the local zone is. For me in zone 9, this means I can keep a yellow Allamanda, rated for zone 10 outside and growing year after year. Yes, it look ratty in the winter but I donít have to lug it in. and it bounces back wonderfully in the spring.
South and Western exposures are usually the best sides to take advantage of when using this method of keeping tropicals plants outdoors in cooler areas.
Not all tropicals will fare well in cooler temperatures and finding information regarding some of the newer introductions will be a matter of your own trial and error in many instances.
How to Grow Globba Gingers
Globbas are easy to cultivate. After a decade of trying different ones, I have come up with several that are incredibly easy to maintain in Zone 8 and higher. The secret to keeping Globbas is in understanding their lifecycle.
All the Globbas I keep in my collection are deciduous. They are a product of their native habitat with distinct rainy and dry seasons. During the rainy seasons, Globbas grow and bloom in a race to reproduce and grow before the dry season sets in. In the dry season, Globbas lose their upper foliage and simply reside underground. During active growth the great foliage and spectacular flowers of Globbas really make up for the lack activity experienced during the dormancy period. The best time to buy Globbas is during the dormancy phase. Roughly, the dormancy and growth periods are about six months.
Globbas like very bright light but direct sun can burn them quickly. In climates like Houstonís I keep them in filtered light for most of the day in a raised bed. I have not heard of Globbas setting seed in North America without hand pollination but the rhizomes can be divided to increase the number of plants as they grow.
A good well draining potting mix or location is essential to successfully keeping Globbas. During active growth, they like consistently readily available moisture and they appreciate regular feeding with a balanced fertilizer. For plants that I keep in the ground outdoors, I water them every day and timed irrigation helps. The enemy of Globbas and nearly all gingers, is too much moisture. The well draining aspect of a Globbaís home is important, otherwise rot can set in.
While dormant, it is critical to lower the frequency and quantity of water without letting the potting mix dry out completely. Globbas kept too wet during dormancy can rot in an astoundingly quick time. As a general rule, never let gingers stand in water. For colder climates, Globbas can be pulled from the ground and kept indoors during the dormancy period. I have actually kept rhizomes in paper bags in drawers until April when I plant them out. It may best to keep them in containers as shortened growing period may affect performance.