Where to locate drip emitters is paramount to a drip irrigation system.
Any irrigation system must make sure that water penetrates the surface of the soil and percolates down through the soil, saturating each soil level and effectively sending the "wetting front" down past the root zones.
Water must reach root zones. That’s the only way that any irrigation system succeeds.
Sprinkler systems are only 50 to 70 percent effective in getting water into root zones.
In a successful drip system, emitters release 90 percent of the water slowly and directly into the root zones of the plants.
But improperly placed emitters in a drip system can be as bad as no drip system at all. So where do the emitters go?
Plant Needs
First, the gardener designs the drip system to meet the needs of the plants.
Emitters should be placed right over the rootballs of newly-installed plants.
For herbaceous and smaller perennials, emitters are usually permanent installments, because the plant’s root system is small, and grows relatively slowly.
Trees and shrubs expand their root systems and grow in girth. Emitters should be moved out from the trunk as the plant grows. Also, for larger plants like trees, as the emitters are moved away from the trunk, new emitters should be added.
There are exceptions. Native and regionally-adapted plants survive on rainwater alone. Therefore many of these plants will not need additional water.
How Much Water?
Perennials
If soils are clay or loam, two drip emitters which deliver water at a rate of ½ gallon per hour are needed for herbaceous perennials.
Shrubs and Small Trees
Shrubs between one and five feet tall, and small trees (less than 15 feet high) need about two emitters flowing at a rate of one gallon per hour. The emitters should be placed about a foot from the base of the plant.
Medium Trees
As trees grow, more emitters are needed. Between 15 and 25 feet tall, trees require at least four emitters, located two feet from the trunk.
Large Trees
Trees taller than 25 feet are much more difficult to water with drip irrigation methods. Increase the number of emitters and increase the flow from two gallons per hour to four gallons per hour.
Soil Type Matters
Water tends to move laterally through soils with more clay in them. Sandy soil allows water to infiltrate down quickly.
If the soil is sandy, put the emitter a foot apart; a foot and a half in loam, and two feet apart from the plant in late summer.
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