In the Garden:
Southwestern Deserts
May, 2012
Regional Report

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(TOP) Sun is high in the summer sky. (Bottom) Sun is low in the winter sky, creating longer shadows at noon. Reprinted from Earth-Friendly Desert Gardening, Arizona Master Gardener Press.

Xeriscape Part I: Planning & Design: Assessing Your Site

Xeriscape design includes a set of seven principles to guide you in the creation and long-term maintenance of a colorful, earth-friendly landscape that suits your unique needs. My last report included ideas to help you brainstorm what you want from your landscape. Next we'll assess your site and sketch a basic diagram for the planning process.

You don't have to be an artist or draftsman to do this! If you have design software, dig in, but otherwise, a simple pencil-on-paper sketch works fine. Start by drawing an outline of your lot's shape. Add the house and existing fixed elements such as hardscape (driveway, patio, sidewalk, pool), fences, trash receptacles, and power lines. Include elements on neighboring properties if they may have an impact on your design, such as the need for screening, maintaining a distant view, or blocking traffic noise. Mark the directions N, S, E, and W on your sketch.

Your sketch will be a work in progress. You may find yourself modifying it over time as you observe how the factors listed below change naturally through the year in your landscape.

Seasonal Sun Angles
The sun's angle changes through the year. In summer, the sun is high in the sky, almost directly overhead, which creates very short shadows at noon. The sun is at its highest point in the sky on the summer solstice. In winter, the sun drops lower in the sky toward the south, reaching its lowest angle on the winter solstice. Why does this matter in your landscape?

In winter, because of the sun's low angle in the sky to the south, buildings may cast long shadows, causing areas to the north of structures to be in full shade. However, in summer, when the sun is directly overhead, those same areas may receive full sun or very limited shade. On your map, mark sun angles in summer and winter and note areas that receive full sun or shade.

You'll eventually use this information to incorporate "passive-solar" techniques into your design. Passive-solar helps you position appropriate plants or other elements such as window awnings or patio covers to reduce heat and glare for outdoor recreation spaces, as well as promote energy efficiency. For example, shading the southern side of a home, where it is exposed to the sun for the longest period in summer, will reduce utility bills.

Wind
In the Southwest, we contend with hot summer winds, unpredictable monsoon thunderstorms, and cold winter winds, all of which desiccate plants. Draw an arrow pointing in the direction of typical wind patterns on your property. Of course, many of today's smaller, fenced lots may not be suited for typical windbreak plantings, but adding a blend of trees and shrubs on the side of a property exposed to the prevailing wind can reduce watering needs for the rest of the garden.

Slope and Drainage
These characteristics are important because you can use them to aid in rainwater harvesting. Last month, I enjoyed visiting a Tucson couple who had such an abundance of plant material that their house was barely visible behind it all. The majority of the landscape was irrigated only by carefully planned rainwater harvesting, which they had fine-tuned over the years based upon observation.

On your map, mark the high and low points of your lot, and use arrows to indicate the direction and approximate degree of slope. When it does rain, watch what happens in your landscape and mark areas where rainwater flows naturally. Note areas where water accumulates, such as shallow depressions or in areas of heavy clay soil with poor drainage. Also note any areas where rainwater might come from an outside source that you can divert, such as a sidewalk in front or an alley in back (as did the Tucson couple). Also consider your roof as a "slope" from which water runs off that can be directed where it is needed. On your map, indicate the pitch of the roof and the flow of water off the roof.

Traffic Patterns
Use dotted lines to indicate where humans, pets, and perhaps even wildlife move across the landscape. Do existing paths work to provide the best routes, for example, from the kitchen to the garden or compost area?

Elements on your map may be updated over time based upon your observations. The above descriptions are brief overviews to get you started, but understanding these elements is key to creating a sustainable landscape that allows you to conserve natural resources, time, and money, while blending attractively within our unique region.


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