Considering the Tucson Valley’s Many Climate Zones:
By Eddie Rodieck
Plant selection and landscape design in the Tucson Valley is dictated not only by severe climate variations from extreme high temperature to severe frosts, but also which plants will do best in the various areas of town. In addition, knowing what plants will do well in each environment of your yard and allowing them room to grow must also be considered when selecting plants, shrubs, and trees that will beautify your home for years to come.
Arizona offers a variety of climates from the warmth of the Sonoran Desert to the glory of the snow-capped White Mountains. Different plants flourish in each environment and that is just as true in the Tucson Valley which spreads from Oro Valley and Marana in the west to Vail in the east and Tanque Verde in the North to Green Valley in the south. The Tucson climate itself ranges from a record high of 117°F to a record low of 6°F. While Tucson sees an average high temperature of 83.7°F and an average low of 58.1°F, you need to be aware these are just averages and what the weather is like in the lower Tucson Valley versus the foothills can vary greatly enough to impact what should be planted around your home.
Know Your Area
There are temperature variations throughout the valley that influence how well a plant species will do. For example, begonias are sold in Tucson, but they don’t do well in the winter months here. Additionally, the flats of begonias sold in Arizona are the same ones shipped to California that tell you to plant them in the full sun. While they will do well in the full sun of California, that is not the case in Tucson. The best place to locate begonias here is in the protection of the partial shade or they will die in about three months.
While all varieties of plants are sold in Tucson, not all plants will have longevity. Even though they are sold here in many nurseries, some plants won’t make it beyond six months to a year in Tucson due to climate fluctuation and soil conditions.
Location, Location, Location
We all know that location can be important when determining which plants to select to add that special curb appeal and beauty to the exterior of your home. When considering which plants to add to your landscape, consider the best location for each plant. What is meant for the full shade won’t be able to handle the full sun and vice versa. The Tucson Basin also has four climate zones you should consider when selecting plants for any landscape design. The four zones include:
- The Lower Tucson Basin. This is the flat area between the Santa Cruz and Rillito washes. Plant selection here should be made with the understanding this area freezes almost every winter, but typically not severely. The exception is the 50-100 year extreme frost pattern we have had, three of which have occurred in the last 20 years. Cold, winter air settles like a blanket in the basin areas.
- The high frost zones are located along the Santa Cruz Wash and Rillito River. These areas are guaranteed a frost almost every winter so plants, shrubs, and trees should be selected accordingly.
- The Tanque Verde Wash and Forty Niner Country Club. These areas see extreme cold and frost every year. Most plants that grow in the Lower Tucson Basin will not survive their first winter in this area. The landscape selection here is similar to Flagstaff and higher altitude areas of Arizona as far as frost is concerned.
- The warmer zone micro-climate of the upper bajadas or foothill areas. These areas freeze periodically, but not as much as the Lower Tucson Basin. Cold air settles in the lower areas and subsequently pushes the warmer air up into the foothills which helps prevent it from freezing. Most plants that freeze in the Tucson Basin do not freeze as often in the foothills. Hence for example the name attributed to Orange Grove Road comes from the orange orchards that were growing here in the 60’s due to warmer evening temperatures known as a micro-climate zone.
Selection of the proper plants is a must in order to choose those that will last and keep you from spending money unnecessarily year after year. Verbena for example falls into the category of plants known as the “pretty now and dead later” varieties because they only last a few months as ground cover in Tucson. Between the climate extremes and the soil conditions, 99 percent of verbena planted here will die. Plants like these should be considered more of an annual rather than as a perennial in Tucson for this reason. The California Pepper Tree also falls into this category as they don’t tend to do well because they are highly susceptible to Texas Root Rot and 90 percent of these trees die. Thus, be sure to select plants that are approperiate will do well in your area.
Landscape Design Around the House
Once you have selected the appropriate variety of plants that will do well in your area of Tucson, consideration must be given to other variables. For example, which plants need the shade of your home to protect them versus which plants will flourish in direct sun. Consider the following when designing your landscape:
- Consider plant placement carefully. Shade varieties should not be planted in the full sun and sun-loving varieties should not be planted in the shade of trees or in the shade of the north side of the house. Plants such as bougainvillea and lantana will have significantly less color and blooms due to the lack of sunlight if planted in the shade and certain varieties will burn in direct sun light.
- The potential growth and characteristics of each plant need to be considered as well. Tall and low-lying characteristics, as well as how large each plant gets, should be taken into account. Many designs do not allow for plants to grow. Eventually, the unique characteristics of the initial installation disappear into a dense jungle requiring constant pruning to maintain. For example, one 5-gallon Texas Ranger can grow to be six feet in diameter and height so avoid planting it too close to walkways and drives.
- Consider utilizing succulents and cactus accents, contouring with mounds and soils, and using boulder accents. This saves water and blends well with the natural environment.
Irrigation and Water Needs
Some plants require less water and others require more. The normal irrigation practice around Tucson has been that all plants with dissimilar water needs have been put on the same irrigation line. Homeowners, and even landscape companies, have fallen to the myth that simply regulating water flow to each plant with the emitter outlet is a viable option. This doesn’t work because all of the plants water at the same time more or less, depending on how they are programmed. The fact is some plants need to be watered more frequently and others less frequently regardless of the emitter flow. Consider the specific water needs of each plant and put them on different irrigation zones to solve this problem. To help your plants do their best consider these options:
- Put flower pots on a separate irrigation line to water daily for approximately 15 minutes.
- Fruit trees, particularly citrus, should be put on a separate irrigation line to be watered less frequently, but more deeply once they are established.
- Plants and shrubbery should also be on a separate irrigation line to be watered during the summer months three to four times a week for approximately two to two and a half hours.
- When combining shrubbery on one irrigation line, consideration should be made for the arid varieties versus the tropical varieties that come from California. If these varieties are mixed together, the arid varieties can end up being overwatered and dying.
When hiring a landscape architect, it’s important that they understand the characteristics of various plants and how well they will do in Arizona, specifically the multiple climate zones of Tucson. Should you need assistance with your landscape design or plant selection to beautify your home, the experts at Cherry Landscape will gladly help you in selecting plants that will thrive and designing an oasis in your yard you may enjoy for years to come.