How to Dig a Trench for a Sprinkler or Irrigation System

By the team at Beehive Rental & Sales — Serving Southern Utah's contractors and homeowners since 1994.

Every property in Southern Utah needs a reliable irrigation system. In a region that averages fewer than 8 inches of rainfall per year, your lawn, garden, and landscape depend entirely on a well-designed sprinkler or drip irrigation setup. Trenching is the most labor-intensive part of the installation, but with the right equipment and a solid plan, it is a straightforward weekend project.

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Quick Answer: To dig a trench for a sprinkler system, rent a walk-behind trencher from BeeHive Rental & Sales, set the depth to 8-12 inches (or 18 inches in freeze-prone areas), and trench along your pre-marked layout lines after calling 811 for utility locates. A typical residential system takes 1-2 days to trench. Call (435) 628-6663 for trencher availability and sizing advice.

Key Takeaways

• •Call 811 before you dig — Utah law requires a utility locate at least 48 hours before any excavation, and it is free
• •Walk-behind trenchers are the most popular rental for residential sprinkler installations, cutting an 8-12 inch deep trench in a single pass
• •Pipe depth matters — 8-12 inches for most of Southern Utah, but go to 18 inches at higher elevations near Pine Valley or Kolob where hard freezes occur
• •St. George's rocky desert soil may require carbide-tipped trencher teeth; ask BeeHive Rental which chain works best for your area
• •Browse trenchers and irrigation equipment to see what is available for your project

Why Trench Your Own Sprinkler System?

Professional sprinkler installation in Southern Utah runs between $2,500 and $5,000 or more for a typical residential lot. The bulk of that cost is labor for trenching. By renting a walk-behind trencher and doing the trench work yourself, you can cut the total project cost to $500-$1,500 in materials and rental fees.

Cost Comparison

Even if you hire a plumber to make the final connections to your water supply, handling the trenching yourself saves thousands.

Planning Your Irrigation Layout

Before you fire up a trencher, you need a plan on paper. Poor layout is the number one cause of irrigation problems — dry spots, overspray onto sidewalks, and wasted water.

Step 1: Measure Your Yard

Walk your property and sketch the outline on graph paper. Mark the locations of:

• •Your water meter and main shut-off
• •The house foundation and any structures
• •Existing trees, garden beds, and hardscape
• •Slopes or grade changes
• •Driveways, sidewalks, and fences
• •Hose bibs and any existing irrigation

Step 2: Determine Your Water Pressure and Flow

Connect a pressure gauge to an outdoor hose bib with no other water running in the house. Record the static pressure in PSI. Then measure flow rate by timing how long it takes to fill a 5-gallon bucket with the hose bib fully open. You need these numbers to size your system properly.

Southern Utah water pressure typically falls between 50-80 PSI depending on your location and elevation. St. George city water pressure varies by neighborhood — homes in the Bloomington Hills area tend to have higher pressure than properties near Bluff Street.

Step 3: Design Zones

Each zone is a group of sprinkler heads that run together on one valve. Zone design depends on:

• •Water flow available — Do not exceed 75% of your measured flow rate per zone
• •Head type — Never mix rotors and spray heads on the same zone (they have different precipitation rates)
• •Sun exposure — Full-sun zones may need different scheduling than shaded areas
• •Slope — Grade changes require separate zones to prevent runoff

A typical 1/4-acre St. George lot needs 4-8 zones depending on landscaping complexity.

Step 4: Choose Head Placement and Pipe Sizing

Follow the "head-to-head" coverage rule: each sprinkler should throw water far enough to reach the next head. This ensures even coverage with no dry spots.

Pipe sizing guide:

Drip Irrigation Considerations for Water Conservation

St. George has implemented tiered water pricing and outdoor watering restrictions that are tightened during drought years. Consider drip irrigation for:

• •Garden beds and planter boxes
• •Trees and shrubs (drip rings)
• •Narrow strips along sidewalks and driveways
• •Slopes where runoff is a concern

Drip lines only need to be trenched 4-6 inches deep, making the job even easier.

Equipment You Will Need

Primary Equipment

• •Walk-behind trencher (rental) — The single most important piece of equipment. Cuts a narrow trench 2-4 inches wide and up to 36 inches deep in one pass.
• •Pipe cutter or PVC saw — For cutting PVC pipe to length
• •PVC primer and cement — For solvent-welding joints

Supporting Tools and Materials

• •String line and stakes — For marking straight trench runs
• •Marking paint or flags — For layout lines
• •Flat-blade shovel — For cleaning trench bottoms and digging valve boxes
• •Tape measure (100-foot)
• •PVC pipe (Schedule 40 for main lines, Class 200 for laterals)
• •Fittings, valves, and sprinkler heads per your design

Trencher Types and When to Use Each

For most St. George residential sprinkler systems, a walk-behind chain trencher is the right tool. It handles the rocky desert soil and cuts an efficient, narrow trench in a single pass. BeeHive Rental & Sales carries trenchers sized for exactly this work — call (435) 628-6663 to discuss your project.

Step-by-Step: Trenching for Your Sprinkler System

Step 1: Call 811 for Utility Locates

This is non-negotiable. Call 811 at least 48 hours before you plan to dig. Blue Stakes of Utah will send locators to mark gas, electric, water, sewer, cable, and phone lines on your property for free. Hitting a gas line with a trencher is dangerous and expensive.

Step 2: Mark Your Trench Layout

Using your irrigation design, mark all trench runs on the ground with marking paint or flags:

• •Mark the main line from the water source to the valve manifold
• •Mark each lateral run from valves to head locations
• •Mark head positions with flags
• •Use string lines for straight runs

Step 3: Set Trencher Depth

Pipe depth requirements by zone in Utah:

Set your trencher depth 2 inches deeper than the pipe requirement to allow for a gravel bed under the pipe.

Step 4: Trench All Main Runs First

Start with the main line trench from the water source to your valve manifold location. Then trench each lateral line from the manifold outward.

Trenching tips for Southern Utah soil:

• •Go slow in rocky sections. Do not force the trencher — let the chain do the work.
• •Watch for caliche. A hardpan layer 6-18 inches below the surface is common across St. George. The trencher may hesitate at this layer. Maintain steady downward pressure and let the carbide teeth chew through it.
• •Clear debris frequently. Rocky soil throws more material out of the trench. Keep the trench edges clear so you can see your line.
• •Keep the chain lubricated. Desert dust accelerates chain wear. Check teeth every 100 feet of trenching.

Step 5: Dig Valve Boxes and Head Locations

At each valve manifold location and sprinkler head, you will need to hand-dig a wider area for valve boxes or swing-joint connections. A flat-blade shovel handles this.

Step 6: Install Pipe and Fittings

Lay pipe in the trench, starting from the water supply side:

1. •Dry-fit all pieces first to verify lengths and layout
2. •Prime and cement all joints using PVC primer and solvent cement
3. •Allow joints to cure for 15-30 minutes before handling
4. •Install valves in valve boxes at the manifold
5. •Connect heads using swing joints (flexible risers that absorb impact)

Step 7: Pressure Test Before Backfilling

Do not backfill before testing. Cap all heads, turn on the water, and pressurize each zone for 15 minutes. Walk the entire trench looking for leaks at every joint. It is far easier to fix a leak with an open trench than to dig it up later.

Step 8: Backfill and Compact

Once the system passes pressure testing:

1. •Gently backfill by hand around pipe joints first to protect connections
2. •Backfill the rest of the trench using the soil pile from trenching
3. •Slightly overfill the trench — the soil will settle 10-15%
4. •Lightly compact the backfill by tamping with a hand tamper or walking it down
5. •Water the trench line to help settle the soil

Step 9: Test Heads and Adjust Coverage

Run each zone and adjust head arcs, distance, and nozzle sizes to achieve even coverage. Mark any dry spots for additional heads if needed.

Southern Utah Sprinkler System Tips

Water Conservation Requirements

The Washington County Water Conservancy District encourages efficient irrigation. Consider these practices:

• •Use smart controllers with weather-based scheduling — some local utilities offer rebates
• •Water between 6 PM and 10 AM to minimize evaporation
• •Convert low-traffic areas to drip or xeriscape — rebates may be available
• •Use pressure-regulated heads to prevent misting and overspray

Rocky Soil Strategies

If your property sits on particularly rocky ground (common in the Green Springs, SunRiver, and Desert Hills areas):

• •Use carbide-tipped trencher chain — standard chain will not hold up
• •Consider a mini excavator for the worst sections where a trencher stalls
• •Thread pipe carefully — rocky trench bottoms can damage PVC during backfill
• •Add 2 inches of sand or fine gravel below and around pipe in very rocky trenches to protect against point-loading on rocks

Winterization

Even in St. George, you should blow out your sprinkler system with compressed air before the first freeze, typically in late November. Pipe buried at 8-10 inches in the St. George valley is generally safe, but standing water in above-ground components (backflow preventers, valves) can freeze and crack.

FAQ

How deep should sprinkler trenches be in St. George, Utah?

In the St. George valley (below 3,500 feet elevation), sprinkler pipe should be buried 8-10 inches deep. This depth protects against surface damage while being shallow enough for easy maintenance. At higher elevations around Southern Utah — Pine Valley, Kolob, or Veyo — bury pipe 16-18 inches deep to prevent freeze damage.

Can I trench a sprinkler system myself without professional help?

Yes. A walk-behind trencher rental makes DIY sprinkler trenching practical for any homeowner. The trencher does the hard work of cutting through soil and rock. You will need basic plumbing skills for assembling PVC pipe and fittings, but these are straightforward techniques that do not require a license. BeeHive Rental & Sales provides operational guidance with every trencher rental.

What type of trencher do I need for a sprinkler system?

A walk-behind chain trencher is the standard choice for residential sprinkler installations. It cuts a 2-4 inch wide trench at depths up to 36 inches, which is perfect for irrigation pipe. For St. George's rocky soil, request a unit with carbide-tipped teeth. BeeHive Rental & Sales at (435) 628-6663 can match the right trencher to your soil conditions.

How long does it take to trench a yard for sprinklers?

A typical 1/4-acre St. George lot with 300-500 linear feet of trenching takes 4-8 hours with a walk-behind trencher. Rocky soil slows the process; sandy or loamy soil goes faster. Plan for a full day of trenching plus a second day for pipe installation and testing. Larger properties or complex layouts may take 2-3 days total.

Do I need a permit to install a sprinkler system in St. George?

Connecting a new sprinkler system to your home's water supply requires a plumbing permit in St. George. The trenching and pipe layout itself does not require a permit, but the backflow preventer installation and connection to potable water must meet code. Many homeowners do the trenching and pipe work themselves and hire a licensed plumber for the final connection and backflow installation.

Ready to trench your sprinkler system? BeeHive Rental & Sales stocks walk-behind trenchers, pipe cutters, and everything you need for irrigation installation in Southern Utah. Their team has helped hundreds of St. George homeowners choose the right trenching equipment for local soil conditions. Stop by 1175 Highland Drive, call (435) 628-6663, or browse available equipment online to reserve your trencher today.