Thursday, May 20, 2010

Lawn Irrigation That's Really "Out of Sight"

Lawns, yawns. They aren’t needed as much as they are found. However, there's no better place to have young kids run around and, play badminton or croquet, or necking while watching the stars. (This subsurface approach to irrigation means you can neck at the same time the lawn is being irrigated!)

The latest revolution in irrigation is happening quietly underground, four to eight inches beneath lush, but water-conserving lawns. Although landscape professionals have long utilized the water-conserving efficiency of drip irrigation for most other types of plantings; combining it with lawns has, until recently, been an unsolvable problem.

Now, however, it's possible to irrigate lawns with emitters buried safely beneath the soil's surface that save even more than the 20-50% watering efficiency of surface emitters.

The idea of subsurface lawn irrigation often raises many concerns. What, for instance, keeps the entombed emitter from becoming plugged by soil? The answer is in-line emitter tubing. The emitters, which are located inside this tubing, contain a lengthy internal pathway which is known as a complex, turbulent or tortuous path. (See the illustration here from Drip Irrigation for Every Landscape & All Climates.) When the system comes on, water pressure purges any soil that may have entered the emitter's orifice. The turbulent pathway is also very self-cleaning when sediment is suspended in the water.

Another common concern is the possibility of the emitters becoming clogged with grass roots. This can be prevented by timed irrigations, which should be both frequent (daily or even hourly) and very brief. Depending upon the soil and climate, for only a matter of minutes, or less—depending on the number of start times. Some brands of in-line tubing also come impregnated with a pre-emergent herbicide which kills root growth at emitter openings. (The roll photographed here has the noticeable greenish tube emitters.) While no organic gardener would use the Treflan™ found in the impregnated emitter, it’s toxicity is very low and the chemical does not migrate far from the emitter.

Designers and clients also may worry about unevenly-watered lawns with telltale green-brown-green striping. Mark Dargay, of EH Griffith Inc., (a distributor of TechLine™ in-line tubing) designed the subsurface irrigation for the Market Square project, 12,000 square feet of turf and trees in downtown Pittsburgh, PA. "I was very leery," Dargay remembers, "I envisioned striping of the lawns." After two summers of healthy non-striped growth, he’s "very pleased."

A word of caution: neophytes in drip irrigation should make their first mistakes above ground with visible or mulched in-line tubing before attempting a subterranean "deployment."

Dennis Hansen, a L.A. and Certified Irrigation Designer in Fairfield, CA, advises designers new to subsurface irrigation to "start with no more than 1000 square feet. Or, hire an irrigation designer with enough experience to have a defensible and insurable status."

The details of how to design an efficient system can be found in my book— Drip Irrigation for Every Landscape & All Climates.

P.S. DON’T attempt if you have gophers. Best in urban areas.


Let me know what you think. Visit my web site to learn about my new book on drip irrigation and other gardening books. Thanks, Robert

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