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Tropical plantings for Southwest patios take extra care

By Merritt S. Keasey III and E. Driscoll HuntSpecial to The Christian Science Monitor / June 6, 1980

The wide-spreading leaves of a banana tree or the brilliant flower sprays of a bougainvillea may not be what one would expect to see in a desert patio or entryway. Yet these are only two of the many types of tropical plants that Southwest gardeners may attempt to grow to add a little more color and lush foliage to their desert homes.

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Often the desert gardener becomes interested in tropical plantings after a visit to one of several nearby Mexican cities, such as Hermosillo, Guaymas, or Obregon.

The courtyards, entryways, patios, and streets are alive with the brilliant colors of hibiscus, royal poinciana, jacaranda, bougainvillea, and even the red bird of paradise.

There are also banana trees, avocado trees, papaya trees, and other large-leaved plants, which not only bear fruit, but also provide cool shade for their owner. It's no wonder then that a Southwest gardener may become inspired to stimulate a patio of this nature in his own home.

While the Spanish-style patio with its luxuriant growth is a very tempting challenge, most of the plants found in the gardens of Mexico are very difficult to grow in the United States. One thing that has to be remembered is that all of the cities named above not only are several hundred miles farther south, but they also are at a lower elevation and have considerably warmer temperatures in the wintertime.

Many of the tropical plants that one may choose originate in parts of the world where rainfall is abundant, humidity is high, cloudy days are common, and temperatures, particularly at the lower end of the thermometer, are moderate.

The desert has none of these features. Here the rainfall is less than 10 inches a year in most places, the relative humidity on a summer day often drops below 10 percent, the sun shines fiercely almost every day, and the temperature can vary from as high as 110 degrees, or even warmer, in the summer to 10 or more degrees below freezing on winter nights.

After carefully considering the above climatic conditions, the gardener who still decides to grow tropical plants is faced with a number of problems. The greatest one of these is location.

Since many of these plants grow in shaded areas in their natural environment, they must have shelter from the intense rays of the desert sun. A few types can be planted in the open, but these are particularly susceptible to damage during the cold winter nights, when frost or subfreezing temperatures can occur anytime between mid-November and mid- March.

Another thing to consider when planning location is the seasonal difference of the sun's angle. Such plants as the split-leaved philodendron, for example, which must have shade, will do quite well in the summer when planted beneath an overhanging roof. But in the winter the sun dips lower in the south and may shine beneath the overhang, causing severe scorching of the plant's delicate leaves.

Sun angle is not the only thing that changes. Desert weather is very unpredictable. A tropical plant that has been growing well for several years may suddenly be killed, or at least badly damaged, by an exceptionally cold winter. This was the case in Tucson and other southern Arizona communities during the winter of 1978-79, when the temperatures plunged to as low as 15 degrees F. in some areas.

Many plants perished, while others were frozen back to a few bare stubs.

Water use is something else to be considered. Tropical plants, especially those with large leaves, use a great deal of water. With water rates rising, and predictions of water rationing in the near future for some desert communities, one must consider this carefully before doing any new landscaping.

Wind also is damaging to tropicals, many of which are protected in their native environment by the surrounding larger vegetation. Plants with delicate leaves or stems should be planted in sheltered areas and staked and tied, or even surrounded with netting to prevent excessive wind damage.

Desert winds are very dessicating, while those preceding a summer thunderstorm often reach extremely high velocities for a short time, tearing off patio awnings and upsetting storage sheds.

They also can make a tattered shambles of delicate-leaved plants.