IN THE SOUTHWEST

by M. Douglas Bryant and Ricardo E. Gomez.

M. Douglas Bryant and Ricardo E. Gomez are Extension Horticulturists, New Mexico State University, Las Cruces.

The Southwest region has many plant growth zones because of temperature and precipitation differences due to great variation in elevation. Deciduous tree fruits with high chill requirements such as apples, pears, peaches and cherries are grown in the mountain valleys of Colorado, New Mexico, Arizona and California. Citrus is grown in selected low areas of southern California, Arizona and Texas. Vegetables and fruit crops are grown from below sea level to above 8,500 feet where frost-free days range from 365 to less than 60.

Carefully choose types and varieties of fruits and vegetables adapted to your specific locality.

The Southwest has low rainfall, extremely low relative humidity (often as low as 4 percent), sunny days, high solar radiation, temperatures that are high in daytime but drop as much as 50 F at night, and periods of drying winds that are often hot during summer. Warm, sunny days in mid-winter and late winter followed by sub-freezing temperatures at night make fruit production hazardous in many localities.

Rainfall is usually low and erratic, requiring at least supplemental irrigation. Water for irrigation is limited in most areas and even critically low in places. Water is impounded in reservoirs and dispersed through canals to fields, orchards and gardens, turning barren deserts into lush production.

Areas without access to reservoir water must rely on pumping from underground supplies. However, much of the underground water is high in salts, possibly toxic to plants.

With the rising demand for water by agriculture, industry, and domestic use, most States have passed water use regulations that allocate given amounts of water to each user. Many water/irrigation districts have been closed to additional expansion because of limited water supply.

Some growers and gardeners have installed "drip" or "trickle" irrigation systems which meter a very small amount of water to plants daily. These systems use only a fourth to a tenth the total amount of water applied by the conventional furrow and flood irrigation systems, but are more expensive to install. Mulching with plastic, straw, or grass clippings is a common technique practiced by gardeners to conserve moisture in the and Southwest.

Prevailing wind east of the Sierra Nevada Mountains is from the southwest and is very dry and strong especially during spring. Low rainfall combined with strong, dry winds makes gardening difficult in spring. Soil moisture is lost very rapidly, requiring frequent irrigation for young plants. Blowing sand is a problem from early March to mid-May, cutting off seedlings at ground level. Hail is a hazard to gardens during summer.

In vegetable gardening, give special care to variety selection since Southwestern areas have various types of climates. For example, some varieties of tomatoes do not set fruit well in the hot part of summer (probably due to low humidity and high temperatures), but do set in spring and early fall. Some tomatoes require too long a growing season to be of any value at high altitudes.

Soils vary in texture, and for the most part are alkaline. This alkalinity may present problems, especially to gardeners from humid regions. Most gardening books suggest adding lime or such materials as wood ashes to improve soil characteristics. Their addition would at best be of no value, and might even deteriorate the soil.

Some manures depending on source have a high salt content and may be harmful rather than helpful.

Yet organic matter plays an important role in soil management and this is especially important in the Southwest where water is scarce and relative humidity usually low. Organic matter not only makes sandy soils retain more moisture, but also loosens up heavy or clayey soils.

Since soils and/or water for irrigation are usually salty, fertilizer practices as well as other cultural practices are somewhat different. Very light rains cause some problems because salt is brought to or near the soil surface where seedlings are more apt to be damaged.

Climatic Data for Representative Areas of the Southwest

Because some high elevation areas of the Southwest have short growing seasons, mulching with plastic films is advantageous. About one or two weeks may be gained on the weather. If mulching is combined with transplanting, you can expect another three- to four-day jump on the weather.

Mulching with organic materials is also very useful. It helps fight weeds and conserves water. This is a practical way of adding organic matter to the soil.

Cool season vegetables of excellent quality may be grown as summer crops in the cooler high altitude areas. In other parts, three distinct gardens may be grown on the same plot of land: spring, summer and fall Gardens.

Spring crops will probably be of lower quality than fall crops because temperatures are getting higher when the crop is maturing, exactly opposite to what occurs in fall.

Excellent quality produce may be grown in the Southwest by even a new arrival if factors such as moisture relations, plant varieties, soils and climate are taken into consideration.