Regional Gardening Reports :: National Gardening Association

In the Garden:
Southwestern Deserts
February, 2009
Regional Report

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Multiple valves allow more effective and efficient irrigation.

Effective Plant Watering and Drip Irrigation Part II

Efficient plant watering is intertwined with a well-designed drip irrigation system. My previous report covered the three basics of effective plant watering. This report follows up with details on how specific drip irrigation components influence your ability to water effectively.

Drip Irrigation Components
Controller (or timer). A controller automatically turns the irrigation system on and off. Different plant types (trees, shrubs, groundcovers, succulents, annual flowers, lawn) require different amounts of water applied at different intervals during different seasons. Thus, an effective controller should allow run times of at least 2 or more hours and intervals of at least 14 days or more. Longer is better in both cases: many desert-adapted plants can last 30 or more days between watering in winter, if they have been properly established. Varied range permits scheduling the correct length of time for water to soak deeply enough through each plant type's root zone, i.e., the 1-2-3 Rule described in the last report.

Valves. Individual valves release water through an irrigation line to reach a specific set of plants. A separate valve for each plant type allows the system to turn on at different intervals (e.g., daily, every other day, weekly, biweekly, monthly) and run for varying lengths of time, depending on that plant type's requirements. Although multiple valves are an extra upfront expense, they pay off in the long-run with efficient watering and long-lived plants. It is not possible to effectively water different types of plants on the same valve line. For example, if water runs long enough to irrigate trees to a depth of 3 feet, everything else is grossly overwatered. In addition to waste, overwatering is unhealthy for plants, causing root rot and death. If water runs short periods for shallow-rooted plants, other plants are underwatered and salt burn also becomes a problem. Unchecked, salt burn will kill plants.

Drip Emitters. Emitters drip water at a slow rate, such as 1, 2 or 4 gallons per hour (gph). There are many styles and gph rates available. A 1-gallon emitter running for 30 minutes applies only 2 quarts of water. (Imagine pouring the contents of a couple Big Gulp glasses on a landscape plant -- it's not nearly enough to soak deeply through a root zone!) Either the controller needs to be able to run as long as needed for emitters to apply sufficient water, or more emitters with higher flow rates can be added.

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