Tropical plantings for Southwest patios take extra care

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.

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.

Among the most favored of tropical plants in the desert garden is the bougainvillea. This climbing plant greatly enhances the appearance of any carport or patio wall. While its flowers are yellow and quite tiny, it is the leaflike bracts that surround the flowers which are large and colorful.

These vary greatly in color depending on the variety: white, salmon, pink, purple, orange, and bright red.

They tolerate full sun and do well in almost any kind of soil. Yet they cannot take cold temperatures. All but those that are planted in the very warmest and best-protected spots are frozen back almost every winter.

Banana trees are fast-growing, with extremely large leaves, and are therefore an enticement to the desert gardener. They are not readily available in most nurseries, however, and usually have to be ordered. They do quite well in a courtyard or entryway during the greater part of the year, although their leaves may become ragged because of wind damage. Very few desert winters go by without at least a few subfreezing nights. This can reduce the banana plant to a leafless stub, and it will seldom grow to fruit-bearing size.

The flowering hibiscus is another favorite. Several types are available in local nurseries, but the most popular one is that with three- inch-wide scarlet flowers. These flowers and the plant's deep-green foliage combine to make the flowering hibiscus an extremely attractive plant.

In Mexico the hibiscus becomes a bush that grows to well above the height of a man's head. In Arizona, by contrast, it seldom reaches half these proportions , because of the freezing temperatures of winter.

Giant reed and giant bamboo are often grown as screening plants. Because of their rapid growth they can reach extremely large proportions during a single growing season. The edible fig, the silk tree, and Texas ebony are small trees that greatly add to the attractiveness of a yard or patio. All are frost- sensitive, however. Some people plant vegetation of this nature, well knowing in advance that they will lose some of them. What they do is replace them when necessary.

Pampas grass, queen's wreath vine, bottlebrush bush, Natal plum, certain palms, and citrus trees are other tropial plants available in desert nurseries. Some do quite well in certain areas.

One thing that a desert gardener must keep in mind is that not even all parts of the same city are alike when it comes to climate. One may be able to grow many of these plants in one part of town, while a few miles away in another area they are quite impossible to maintain.

The reason for this is that during the night the cold air flows downward from the foothills and mountains, layering in the lowest areas, particularly along arroyo, or riverbed, courses. People who live in these parts simply cannot grow many of the delicate tropical plants. It is interesting to note that residences built in the warmest areas of a desert city -- the so-called banana or citrus belt -- usually bring the highest prices on the real-estate market.

The ideal way to grow tropical is, of course, in a greenhouse. There the gardener can completely control the environment, adjusting the temperature and humidity with the twist of a knob. Greenhouses, however, may be expensive and entirely defeat the original idea of having a patio that looks like something from south of the border.

Often a lath-house-type of covering over part of the patio or entryway will offer a good deal of protection from the desert sun as well as frost.

Tropicals in such areas will still freeze, however, on the coldest winter nights. The answer here is to cover them with blankets or tarpaulins; or, as some homeowners do, protect them with outdoor radiant heaters or sun lamps.

Probably the best solution, although not necessarily the easiest, is to plant all of one's tropicals in containers. This way the plants can be moved to various locations, depending on the time of year. During extremely cold periods they can be grouped together in a garage or carport, or whatever other place offers the most protection.

Too much heat, too much cold, excessive wind and dryness -- these are just a few of the desert conditions that make growing tropical plants rather hard. Still, despite all the problems, many people find it a challenge that's well worth the trouble.