In the Garden:
Southwestern Deserts
September, 2012
Regional Report

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As plants mature in a xeriscape, irrigation frequency can be reduced.

Xeriscape Part IV: Irrigation: Plant Water Use Basics

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. Previous reports covered design and site analysis, whether to install turf, and varied plant selection subjects. The next topic area will cover watering effectively with drip irrigation systems.

I bet if every nursery employee in the Southwest received a dollar each time they were asked, "How often should I water?," they could all retire to Fiji at a young age. (I know I'd be in the South Pacific now if I'd had the foresight to request a buck up front.) Most people want a quick and easy answer to watering questions, but unfortunately, there is no such response. Many interrelated factors influence a plant's water needs. This, in turn, influences how to design an efficient drip irrigation system. Let's start with factors that can help you understand your plants' water use.

Soil type Clay soil retains moisture longer than sandy soil. However, the same amount of water penetrates more deeply through sandy soil than clay. For example, 1 inch of water penetrates about 1 foot through sandy soil but just 5 inches through clay.

Plant type Are you irrigating trees, shrubs, groundcovers, cacti, perennials, annuals, or turf? Larger plants develop deeper root systems that are better able to withstand short-term changes in weather and soil moisture. Annual plants in containers may need daily watering during hot weather.

Maturity Older plants with well-established root systems can be watered less frequently than young transplants.

Adaptability Native or desert-adapted plants thrive for longer periods with less water than plants from temperate or tropical regions. Some natives will survive on rainfall after establishment (assuming average rainfall), although they may look more attractive in a landscape setting with supplemental water during long dry spells.

Growing season Plants use more water during active growth periods. Overwatering during dormancy (winter for most) promotes root rot.

Weather Plants use more water on sunny or windy days. Soil dries out faster in summer than winter.

My next report will continue the topic of effective irrigation.


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