Southwest Gardening Zones

The Challenge of Gardening in the Southwest

If you take a trip to your nearby bookstore and peruse the garden section you’ll see a wonderful selection of garden books. Many of these are full of photos of lush gardens filled with hydrangeas, rhododendrons and other gorgeous plants that haven’t a prayer in a Southwest garden. Unlike the authors of those books, we live in a dry climate where rainwater is in short supply, but sunshine is ample. This is why we decided to create Southwest Gardening as a source of realistic – but optimistic – information on how to grow plants in our arid part of the continent. Our climate challenges don’t prevent us from having beautiful gardens.

sonoran desert rain
Rainy day in the Sonoran desert.

When we refer to zones in our blog posts, we’re using the U.S. Department of Agriculture (USDA) hardiness zones, which are assigned mostly based on low temperatures that affect plant survival. Another source for Southwest gardeners is the Sunset climate zone map.

Zones and climate are important when choosing plants for your home garden. Here at Southwest Gardening, we can help you feel more confident in choosing and caring for plants you love, even in Southwest climate extremes.

Arizona’s Low Desert

low desert landscape.
Low desert landscape.

The deserts of Arizona are known for their heat. In Phoenix and and other low deserts of the state, the summers are long and hot. Our highs typically hit the century mark 110 days per year and can exceed 115 degrees. The low desert has mild winters, with seven or fewer days of freezing temperatures. Our growing season lasts from mid-February through late November. We can grow vegetables nearly all year long, and start cool-season plants in mid-September and October. We plant warm-season vegetables in March.

Two rainy seasons provide our average annual precipitation of only 8 inches. Some of the rain comes in winter, but torrential rainfall can sweep through the desert during summer monsoons. The desert is lush, filled with small, shrubby trees and columnar cacti. Home gardeners can mimic nature in their landscape and add a few native flowering plants, even some tropical and sub-tropical plants with a little extra care. The low deserts of Arizona include Phoenix and Yuma. Tucson is considered intermediate desert.

Southwest Intermediate Deserts

garden-in the middle desert
Middle desert yard.

The intermediate deserts of the Southwest include areas of the Chihuahuan, Mojave, and Sonoran Deserts found in Arizona, New Mexico, Nevada, and Texas.  While most people think of deserts as dry and hot, these intermediate regions also feature notable wet and cold periods.

Summertime highs over 100 degrees are common, but winter lows in the teens are also common. Areas that get sufficient hours of cold (called “chill hours”) can grow temperate fruit trees such as apricots and apples. The vegetable growing season is generally year-round, with marked times for planting cool-season or warm-season plants. Many garden favorites such as roses and iris do well here.

In these Southwest deserts, there are two marked rainy seasons. Gentle soaking winter rains off the Pacific Ocean grace the Mojave and Sonoran Deserts.  Torrential summer thundershowers sweep in off the Gulf of Mexico, and fall upon the Chihuahuan and Sonoran Deserts. Some areas commonly get both rains so that the average rainfall in the intermediate desert region is 2.5 to 12 inches, depending on your location.

Local vegetation varies from dense to sparse. If you plan on watering your garden, at least occasionally, you can grow virtually anything from these three deserts in your garden, along with a plethora of arid-adapted plants from around the world, like Greek oregano, Roman chamomile, or palm trees from the Sahara.

The intermediate deserts include El Paso, Las Vegas, Lordsburg, and Tucson.

New Mexico’s High Desert and Mountains

rio bonito
High desert and foothills near Ruidoso, N.M.

New Mexico ranges from the coldest mountain climates to low desert. Most of the state falls within high desert and intermountain climate zones. The high desert areas average 12 inches of rain a year. Closer to mountains, rainfall is a little more abundant. The temperature in mountainous high deserts can vary 15 degrees from canyons and pockets of cool air to nearby sunny slopes. What’s more, high, cool deserts can peak at more than 100 degrees on hot summer days and below freezing several times each winter.

The USDA places Albuquerque in zone 7, with variations from the city’s foothills to its valleys. New Mexico State University Extension divides home vegetable gardening into three areas based on average number of frost-free days and average date of last frost.

The warmest area, 1, covers southern high deserts around and west of Las Cruces, and east from near Roswell to the Texas border. The last frost typically is in early to mid-April.

Area 2, with last frosts typically hitting between April 20 and May 10, covers Albuquerque, most of the Rio Grande Valley from the edge of Santa Fe south, and the Northeastern high plains.

Area 3 is the coldest, with last frosts hitting Between May 10 and June 1. Taos and most of northern New Mexico, along with Gallup, fall into this region.

Texas – From the Panhandle to the Gulf

Texas Rio Grande Valley
The Rio Grande in southwest Texas.

Few states have more varied gardening zones within their borders than Texas. This is not merely because of its size. The Lone Star State stretches westward from the edge of the Mississippi Delta to the Chihuahuan Desert, from the Panhandle in the north to the southern sweep of the Gulf Coast, ending in Brownsville.

Texas is divided into five gardening regions. Click here to see the map developed by Texas A&M. The dividing lines are the same as the USDA cold-hardiness zone maps but you’ll need to know a little more than that to garden in these regions. Here’s a quick rundown of each zone.

Zone I – This dry region covers the Panhandle, a region dominated by weather coming south off the Rockies or from Canada and the Great Plains.

Zone II – Stretching from the western deserts to the Piney Woods in the east, this section could really be divided into two parts. The largest section, including Lubbock and El Paso, is generally thought of as West Texas with a steady dry climate all its own. The eastern section, bordered as it is by the Red River and the Mississippi Valley, has a higher rainfall and more moderate temperatures.

Zone III – Of all the garden zones in Texas, this has probably the most varied growing conditions. Gardens here are buffeted alternatively by weather coming down from the Great Plains or sweeping up from the Gulf of Mexico. These opposing forces do battle with the occasional storm front off the Pacific that passes through the Southwest.

Zone IV and V – Moving south we reach an area dominated by the Gulf Coast to the west and the highland desert areas to the west. G.ardening here is year-round.