Irrigation Layout Planning Guide

A well-planned irrigation layout is mostly arithmetic done before the trencher starts. The failures we get asked to diagnose — dry corners, misted sidewalks, zones that gasp — are layout problems, not product problems. In Texas, remember that installing or altering irrigation requires a licensed irrigator (TCEQ); this guide covers the planning conversation that makes you a better partner on that work.

Start with supply: two numbers

1. Static pressure: gauge on a hose bib, all water off. Design sprays around 30 PSI at the head and rotors around 45; if static is under about 50 PSI, plan smaller zones. Over 80 PSI, spec a pressure regulator — misting heads waste a third of their water.
2. Available flow: time filling a 5-gallon bucket from the main-adjacent bib. Thirty seconds to fill is 10 GPM; twenty seconds is 15 GPM. A hose bib understates the main, so treat the result as a conservative number. Design zones at no more than 75 percent of available flow.

Zone by plant water need, then by precipitation rate

Hydrozone first: turf, shrub beds, color beds, and native/low-water areas each get their own zones because they get different run times. Then never mix head types in a zone — sprays apply water three times faster than rotors, so a mixed zone drowns one area to wet another.

On our clay, which absorbs only about a tenth to a quarter inch per hour, rotary nozzles and drip are the workhorses, and even they need cycle-and-soak — standard sprays exceed intake rate almost immediately, which is why cities require cycle-and-soak programming. Convert bed spray to drip wherever plants are the target; it is also the answer to head-height conflicts in maturing shrub beds.

Coverage rules

• Head-to-head spacing: every head throws to its neighbors. Stretching spacing to save heads creates the donut-shaped dry spots you see in August.
• Perimeter-first layout: heads along edges and corners spraying inward, then fill the middle. Part-circle heads at edges keep water off pavement and fences.
• No spray zones wider than the throw allows — a 4-to-5-foot-wide parkway strip is a side-strip nozzle or drip application, not a 15-foot spray head throttled down; strips under 48 inches should be drip.
• Separate sun and shade turf onto different zones where possible; shaded St. Augustine needs half the water of full-sun bermuda.
• Sleeve under every hardscape element at rough-in: 4-inch sleeves for laterals and wire, at double the pipe count you think you need.

Zone count math

Sum the GPM of every head in a proposed zone (nozzle charts list it — a typical 15-foot spray quarter is about 0.9 GPM, a rotor 2 to 4 GPM). Divide total demand by your 75-percent flow budget to get minimum zone count. Example: 48 spray heads averaging 1.5 GPM is 72 GPM of demand; on 12 GPM of usable flow, that is six zones minimum — plan seven so no zone runs at the ragged edge and pressure stays crisp.

Put the as-built zone map in the closeout package — future-you, diagnosing a dry spot in two years, will be grateful.