5 Common Mistakes When Installing Underground Irrigation (and How to Avoid Them)

Installing an underground irrigation system can transform your landscape, saving you time and water while keeping your lawn lush. But the process is more complex than just digging trenches and connecting pipes. Even experienced DIYers can make mistakes that lead to poor coverage, broken components, and sky-high water bills. Understanding the most common pitfalls before you start can save you hours of rework and hundreds of dollars in repairs.

Whether you're upgrading an existing system or starting from scratch, this guide walks you through five frequent errors people make when installing underground sprinkler systems—and how to avoid them. From trenching depth to valve placement, we'll share practical tips that help you get it right the first time. And when you need reliable components, Orbit offers durable solutions like smart timers and impact rotors designed for long-lasting performance.

Mistake #1: Trenching Too Shallow or Too Deep

One of the most common underground irrigation mistakes is improper trench depth. Digging too shallow leaves pipes vulnerable to damage from lawnmowers, foot traffic, or freezing temperatures. On the other hand, digging too deep wastes effort and can make repairs difficult. For most residential systems, main lines should be buried 10 to 12 inches deep, while lateral lines can be 6 to 8 inches deep. Always check local frost lines—if you live in a colder climate, you may need to go deeper to prevent winter pipe bursts.

Before you start, call 811 to mark underground utilities. Use a trenching shovel or a rented trencher for clean, consistent depth. Mark your planned pipe routes with string or spray paint to avoid guesswork. Remember that slopes and curves require gradual bends—sharp angles can stress fittings. If you use push-to-connect fittings like those from Orbit's PVC-Lock line, you'll appreciate how easy it is to make secure joints without glue, but proper alignment is still essential for a watertight seal.

• Always verify local frost depth before digging.
• Use a string line to maintain consistent depth across long runs.
• Consider using a trenching machine for large yards to save time and ensure uniformity.

Mistake #2: Incorrect Pipe Sizing and Material Selection

Pipe sizing errors can lead to pressure loss, uneven coverage, and inadequate water flow to sprinkler heads. Many DIYers use pipe that is too small, restricting flow, or too large, which increases costs and complicates fittings. For most residential underground systems, 1-inch or 3/4-inch PVC or polyethylene pipe works well for main lines, while lateral lines are often 1/2 inch. Always calculate your system's total flow rate (GPM) and pressure (PSI) to choose the right diameter.

Material selection matters too. PVC is rigid and best for straight runs under pressure, while polyethylene (HDPE) handles curves and is freeze-tolerant. Orbit's Blu-Lock and PVC-Lock systems simplify connections with push-to-fit technology, eliminating the need for clamps or glue. For example, the 1/2" PVC-Lock x 1/2" FPT Elbow 33775 makes a tight corner connection without primer or glue, saving time and reducing leak potential. Choose the material that best matches your soil and climate.

• Use a pressure gauge at the hose faucet to measure your static PSI.
• Calculate total GPM by running a bucket test (fill a 5-gallon bucket and time it).
• Match pipe size to the flow demands of your largest zone.

Mistake #3: Poor Valve Box Placement and Wiring

Putting valve boxes in inconvenient locations is a frequent oversight. Valves should be accessible for maintenance but not in the middle of a driveway or under a future patio. Also, burying them too deep makes them hard to find and work on. Place valve boxes near the water source but slightly elevated to prevent water pooling. Ideally, group multiple valves together in a single box for neat organization.

Another common error is improper wiring for electric valves. Using wire that is too thin or failing to seal connections leads to short circuits and solenoid failures. Use direct-bury irrigation wire (minimum 18-gauge) and watertight connectors. If you're installing a smart controller, such as the Battery-Powered Sprinkler Controller 57865, ensure you run enough wires to each valve station and label them clearly. This controller runs on batteries, making it ideal for locations without AC power, but proper wire sealing is still critical to avoid corrosion.

• Place valve boxes at least 12 inches away from walls or fences for easy access.
• Use silicone-filled wire nuts or gel-filled connectors to prevent moisture ingress.
• Run a spare wire (or two) to each valve in case one fails later.

Mistake #4: Neglecting to Plan for Drainage and Backflow Prevention

Water left sitting in pipes during winter can freeze, expand, and crack fittings. Many DIYers forget to install drain valves or slope pipes properly to allow water to exit. For systems in freeze zones, manual or automatic drain valves should be placed at low points in the main line. Alternatively, use a compressed air blow-out method each fall, but that requires an air compressor and proper fittings.

Backflow prevention is another non-negotiable. A backflow preventer stops contaminated irrigation water from flowing back into your home's drinking supply. Local codes often require a testable backflow device, such as a pressure vacuum breaker or double-check valve. Install it above ground near the water source and protect it from freezing with an insulated cover. Orbit offers reliable backflow preventers that meet code requirements for most regions. Don't skip this step—safety and legality depend on it.

• Install manual drain valves at the lowest point of each zone's main line.
• In cold climates, bury main lines below the frost line and use a blow-out adapter.
• Always check local codes for required backflow prevention devices and testing intervals.

Mistake #5: Choosing the Wrong Sprinkler Heads for Your Coverage Area

Selecting sprinkler heads that don't match your yard's shape, size, or water pressure is a recipe for dry patches and overspray. Rotors work well for large, open lawns, while spray heads are better for smaller areas and beds. Impact sprinklers handle uneven terrain and can throw water far distances. The key is to match head type to your specific zones: use rotors for big rectangles and spray heads for narrow strips or curved borders.

For example, if you have a large open area that needs even coverage, consider the Pulse XL Pop-Up Impact Rotor Sprinkler in Canister 55201. It combines the durability of an impact head with a pop-up design to stay hidden when not in use, delivering consistent water distribution across wide spaces. In tighter areas, a precision spray head like the 4" Professional Spray Head PR with Center Strip Nozzle 80349 offers adjustable patterns and pressure regulation to avoid misting. Testing your system after installation—running each zone and checking coverage—will help you make adjustments before burying pipes.

• Use matched precipitation rate (MPR) nozzles within the same zone to avoid over- or under-watering.
• Check manufacturer specifications for recommended pressure range for each head type.
• Install head-to-head coverage (each head should spray to the next) for even irrigation.

Avoiding these five common mistakes will save you time, money, and frustration while ensuring your underground irrigation system delivers reliable, efficient watering for years to come. Remember to plan carefully, choose quality components that match your specific needs, and test everything before backfilling trenches. For a dependable, easy-to-install smart controller that works without AC power, check out the Battery-Powered Sprinkler Controller 57865—it's a perfect fit for remote zones and retrofit projects. Browse the full Orbit lineup to find the right parts for your next irrigation project.