Southwest Gardening Regions

The Challenge of Southwest Gardening

No doubt about it – our Southwest climate is unique!

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 – 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 Southwest climate challenges don’t prevent us from having beautiful gardens.

sonoran desert rain
Rainy day in the Sonoran desert.
Climate Zones

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

Zones and climate are important when choosing plants for your home garden. We will occasionally also discuss “microclimate.”  One example of microclimate is a sunny south-facing wall in your yard.  That small spot will be even warmer than the rest of your yard.

Here at Southwest Gardening, we can help you feel more confident in choosing and caring for plants you love, even in Southwest climate extremes.


Low Desert of Arizona and Eastern California

low desert landscape.
Low desert landscape. The low deserts include Phoenix and Yuma. Tucson is considered intermediate desert.

The low deserts of the Southwest are best known for their summer heat. In Phoenix and other low deserts areas – the summers are long and hot.  This region includes Yuma, Coachella Valley, and along the lower Colorado River. 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.

Low Desert Division

Much of the region is part of the Sonoran Desert and enjoys two rainy seasons, with central Arizona attaining an average annual precipitation of 8 inches. In the Sonoran Desert regions, some of the rain comes in winter, but torrential rainfall can sweep through the desert during summer monsoons. The Sonoran 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.

Eastern California and westernmost Arizona is part of the Mojave Desert generally get only slow gentle winter rains, very rarely the summer monsoon rains.  Average rainfall is less, around 4 inches of rain per year.  Landscapes can still be lush, and homeowners can include perennials, herbs, flowering shrubs, cacti and other lovely succulents in their landscapes.

Southwest Gardening’s Noelle Johnson lives in the Phoenix Area.


Southwest Intermediate Deserts – Arizona, New Mexico, Nevada, California, and Texas

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, California, and Texas.  Most people think of deserts as dry and hot, these intermediate climates also feature notable wet periods and notable 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.

Intermediate Desert Division

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.

Southwest Gardening’s  Dr. Jacqueline A. Soule lives in the Tucson Area.


High Desert and Mountains – New Mexico, Nevada, Arizona, Colorado, Utah

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

Many Southwestern states range from the coldest mountain climates to low desert. Most of New Mexico 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 between 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. Knowing these areas is helpful for planting new plants and timing when to start a vegetable garden.

  • Area 1 is the warmest area, covering the southern high deserts 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.

Other Southwestern states have similar geography and zone ranges. For example, Salt Lake City ranges from zones 5b to 7 b in its metro area, and Denver ranges from 5a to 7a.

Southwest Gardening’s Teresa Odle lives in New Mexico’s Area 3 (USDA zone 6B), in the mountains of southern New Mexico.


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. This large expanse is mostly flat, leaving the state at the mercy of huge weather changes sweeping down from the Great Plains and up from the Gulf Coast. Temperatures can vary as much at 30 degrees in a 24-hour period. Sunny skies can switch to violent thunderstorm and tornado warning in a few hours.

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.

Texas Zones
  • 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. Summer highs average well into the 90’s. Winter often has sustained sub-freezing temperatures in January and February.
  • 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 (up to 35 inches) 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. Rainfall varies from 14 to 30 inches per year.
  • 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. Gardening here is year-round but requires plants to endure high temperatures and high humidity. Average rainfall is 40-60 inches, with much more when a hurricane hits.

Southwest Gardening’s Ann McCormick lives in Texas.