Traditional subtropical gardening, it must be confessed, generally requires a high input of water to be successful. In western climates, this means that irrigation is required to sustain the garden through the summer. Subtropical gardening requires about as much water per land unit as keeping a green lawn. A few require much more. Most plants used in subtropical gardens will survive without summer water in a dry summer climate, but will not thrive so that the garden is lush and achieves its full potential. Many xeric plants can of course be used in subtropical gardens, and are often under used (7).
In considering the effects of the prediction on subtropical gardening, one must be careful to remember that subtropical gardening is primarily an urban phenomenon. So the part of the prediction which states that less water will go to irrigated agriculture does not directly apply to subtropical gardening in the sense that the two are closely related. Subtropical gardening falls under the category of urban water usage, and can be included in those activities such as golfing that take water away from farmers. "The largest single residential use of water is landscape irrigation, accounting for 40-70% of domestic water use for typical residences. These quantities can be reduced through careful design and management" (3).
Nevertheless, subtropical gardening may not be considered an urban water need once the stresses are high enough, and thus, it will be affected dramatically. That is, if there is only enough water to drink, wash and cook with; no one is going to squander it on thirsty plants when other possibilities exist. To begin with, many would consider the health of their gardens so much less important to their well being than the more obvious water needs people have, that they would be inclined to neglect their gardens completely. This is debatable, and fortunately there are alternatives.
Xeriscaping
Xeriscaping is a viable alternative to traditional subtropical gardening, and deserves to be covered in detail. It is a gardening technique which takes into account the saving of water and the adaptation of the garden to a region's natural cycles of wet and dry seasons, and drought (13). In drought prone climates (which includes almost all climates people garden in), it means that drought tolerant plants must be used, and other measures taken to maximize the conservation of water (2, 13).
There are seven basic principles to xeriscaping, which are reasonably self-explanatory:
One key concept in an xeriscaping scheme is the oasis (2, 13). Xeriscaping does not completely exclude the use of thirsty plants--it simply demands that they be kept to a minimum, and kept in one small area, or perhaps two, in the garden (13). Thus, oases of more thirsty plants can be incorporated into the landscape to include some of the usual water-loving subtropical plants such as palms and bananas. If oases are incorporated into the garden plan such properly, they can drastically effect the overall appearance of the garden. Generally they tend to be located close to the house, so that evapo-transpiration can help keep the house cool (13).
Xeriscaping can even be applied in climates that are thought of as "wet", such as western Washington (10). Native Washingtonians know that it does not really rain all the time in western Washington, and that lawns and gardens must be watered copiously if they are to remain green throughout the summer and fall. However, there is a large spectrum of plants that tolerate wet winters and dry summers both, and many of them remain very underused, and look very subtropical in appearance. Such genera as Arctostaphylos, Fremontodendron, Carpenteria, Convolvulus, Cistus, and Eucalyptus come to mind.
Other applications
Even if the idea of xeriscaping does not have appeal for a given situation, one can still consider pushing the limits to see just how little water the existing garden will survive on before it starts to suffer. Frequently it is discovered that the garden may be living on twice as much water as it really needs. This is especially the case with lawns, which are often grossly overwatered by ignorant people.
The wasting of water through plumbing and other water transport systems has already been mentioned. It is important to ensure that one's irrigation equipment functions properly and does not waste water (13).
A vast knowledge of plant material, and especially of drought tolerant plants, is essential to a subtropical looking xeriscape. So many potentially useful plants exist and yet remain rare for no legitimate reason.
In a world where water use continues to deplete the available amount of water in the ecosystem, xeriscaping can without question be considered the gardening trend of the future. When people run out of water, they will have to change their gardening habits whether they want to or not.
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