Planting Guidelines for Spring: Southwest

The Southwest is a region of geographical extremes -- deserts, mountains, flatlands and coastal lands -- as well as weather extremes marked by varying temperatures. Microclimates within the borders of Southern California, Nevada, Arizona and New Mexico can alter gardening conditions within a few miles of each other.

“The Southwest has wonderful weather, but we have water issues that require irrigation,” said Jackie Brooks, master gardener program coordinator for the University of California Cooperative Extension Office for San Bernadino County, California.

“I don’t think it’s harder to put a plant in the ground in the Southwest than it is elsewhere, but I do think to be successful, you need to do more research and spend more time in caring for the plants.”

Dennis Swartzell, a horticulturist consultant based in Las Vegas, Nevada, knows all too well about the extreme temperatures in the Southwest.

“We have a sizable number of days -- more than 90 -- that are 100 degrees [Fahrenheit] or higher, which is pretty intense,” Swartzell said.

The 2012 USDA planting guidelines, which are based on the average annual minimum winter temperature, show the diversity of the region. The coldest areas registered as a 4b, with the temperature registering -25 to -20 F. The warmest was 10a, with temperatures ranging from 30 to 35 F.

“We have high deserts, but we have super cold [spells] as well. It makes for an interesting growing season,” said Sam Thompson, a master gardener and the volunteer organizer for the Sandoval County Extension Service of New Mexico State University.

To help the plants cope, shading is often used to shelter them from the sweltering heat.

"The sun simply gets too intense for most plants,” Thompson said. “Full sun at 5,000 feet is not the same as full sun at sea level. You have to provide shade for some of the pickier crops, like corn, to survive."

Shading has another benefit.

“It helps when we get our frequent high winds that also damage plants,” Swartzell said.

Dripping Water Is a Lifeline for Southwest Plants

Water -- or the lack of dependable rainfall -- is a constant challenge for gardeners in the Southwest.

“You cannot rely on natural rainfall,” said Dennis Swartzell, a horticulturist based in Las Vegas, Nevada. “You need to provide water every day to the plants; sometimes, twice a day. Proper irrigation management is vital."

Sharon Petterson, co-owner of Gardener’s World Nursery in Phoenix, Arizona, says gardeners must water daily.

“Sometimes it’s just using a water hose, but a lot [of people] use irrigation systems that have a time clock to water the lawn and garden,” she said.

Many native plants, such as the Arizona cypress, desert willow, agave, cactus and native sages, have evolved to be able to survive without a lot of water. But vegetables and most flowers need daily watering, especially in the warmer months with high evaporation rates.

The irrigation drip sends water to the plant’s roots via narrow tubes. Petterson recommends the system run at least two hours per irrigation, longer when the temperatures are higher than 105 F. Even with that system, some plants may need more water.

“You need a water system to sustain plant life, not drown plants,” Swartzell said. “A lot of people think with water that more is better. It’s a very fine line.”

Soil Prep

Soil preparation is a must because most of the desert soil is “absolutely awful,” said Swartzell. Acidity or alkalinity is measured in pH units. A pH of 7 is neutral. Soil in the area tends to have high pH levels of 8 to 8.5.

Desert soils vary tremendously. Some are sandy and gravelly, while others have concentrations of sticky clay or white limy layers. In the arid parts of the Sonoran Desert, a small layer of small stones can cover the soil surface, says Sharon Petterson, co-owner of Gardener’s World Nursery in Phoenix, Arizona. On top of that, the soil is a major challenge because its alkaline factor.

“The first step is to use a soil acidifier to break the acid down," Petterson said. "After you neutralize it, then you can fertilize it."

Thompson says growing conditions even a few miles apart can be vastly different.

“I live four miles from the Rio Grande River, and there are plants that I can grow at my house but I can’t at the community garden that is by the river. I have a longer season. The river soil is more sand, and by my house, it’s more clay. I can grow heirloom tomatoes where I live, but we grow hybrid tomatoes by the river.”

But no matter where a garden is in the Southwest, a gardener can't go wrong with a few standard crops.

“We grow everything that you make salsa with,” joked Swartzell.

Winter is perhaps the most fertile time for planning in the region.

“Things that most people back East plant in the spring, we plant in the winter,” Swartzell said, citing plants such as beets, cabbage, tomatoes, broccoli and onions that should go in the ground in February. February is also a good planting month for pansies, geraniums, snapdragons and bulbs, such as callas, amaryllis and spider lilies.

According to the Arizona Cooperative Extension Office of the University of Arizona,

corn and several varieties of bean -- warm season crops -- can be planted and harvested until the first hard frost.  Root vegetables and salad greens such as kale and lettuce may survive throughout the winter.

It's all a lot to remember, but Swartzell maintains a sense of humor about the challenges of Southwestern gardening.

“After you deal with the general conditions of high and low temperatures, the rain situation, absolutely lousy soil and frequent high winds, then growing plants and flowers in the Southwest is a piece of cake.”