Spring Startup for Drip Irrigation: What to Test Before You Turn the Water On (And What Skipping It Costs)

Every spring I watch the same thing happen. Someone walks out to their drip system after six months of sitting idle, cranks the valve open, and expects everything to work like it did in October. Half the time they get lucky. The other half they get a geyser from a split fitting, a pressure regulator stuck wide open, or emitters that haven’t seen a flush since the Bush administration.

Spring startup is not winterizing in reverse. Stuff happens while a system sits. Rodents chew through tubing. Freeze-thaw cycles crack PVC joints you swore you drained. Filter screens rust or split. And even if nothing broke, the first blast of water through dry lines picks up every flake of mineral scale and biofilm residue that dried onto the inner walls all winter.

Here’s what needs to happen before you open that valve, in order, with real numbers on what skipping each step costs.

Start at the Water Source, Not the Drip Lines

Most people sprint straight to the field and start inspecting emitters. Wrong order. If your water source has a problem, you pump that problem through every inch of your system.

On a well, check the pump first. Look for rust around the casing, listen for grinding on startup, and run it for 30 seconds with the discharge going to waste. If the water comes out brown, you’ve got iron bacteria that multiplied over winter in the well column. Shock it with chlorine before anything else. A pump rebuild runs $400 to $1,200 depending on horsepower. Catching a failing bearing in April costs a few hundred. Ignoring it until it seizes in July costs the full rebuild plus a week of missed irrigation during peak heat, which can knock 10 to 15 percent off yield on a vegetable crop.

Surface water brings its own spring surprises. Algae blooms start early, especially after a mild winter. If your intake screen looks like a green carpet, clean it before you pull that water into your filter bank. A media filter loaded with algae on the first run channels within minutes, pushing unfiltered water straight into your drip lines. Replacing a media filter’s sand or gravel load costs about $80 to $150 per tank. Cleaning the intake screen costs twenty minutes and a scrub brush.

Inspect Above-Ground Lines Before You Pressurize

Walk every above-ground mainline and submain. Three things to look for:

PVC joint cracks. Freeze-thaw cycles destroy solvent-welded connections if any water was left in the line. A hairline crack at a glued joint holds at 10 PSI and blows apart at 40. You’ll see white stress marks where the PVC has turned opaque from flexing.

Split polyethylene tubing. UV degradation turns black PE gray and brittle in a single season if the tubing wasn’t UV-stabilized. Squeeze it every few feet. If it crunches instead of flexing, replace that section. A 100-foot roll of 1/2-inch PE tubing runs $25 to $40. That’s cheaper than losing a whole zone mid-season and splicing under pressure with crops in the ground.

Animal damage. Ground squirrels, gophers, and rats chew drip tubing without needing a reason. Look for tooth marks and circular punctures. A single rat hole in a lateral line dumps 60 gallons an hour at 25 PSI. Over a 12-hour cycle, that’s 720 gallons you paid to pump and never reached a plant root. The water cost is pocket change. The real damage is the dry spot in your crop you won’t notice for two weeks.

Flush Before You Filter

This sounds backwards but it isn’t. Open every flush valve at the end of your laterals and submains before water hits your filters. Let the first surge push out all the loose debris, scale, and dried biofilm. Give it two to three minutes per zone, until the water runs clear.

I’ve seen farmers skip this and load brand-new disc filter cartridges with six months of crud in under an hour. A set of disc filter elements for a 2-inch filter runs $40 to $90. Cleaned properly, they last two to three seasons. Plug them solid on day one with silt that should have been flushed, and you’re replacing them.

After flushing, open the filter housing. Hold the screen or disc elements up to the sun. If you can’t see light through more than 80 percent of the surface, they need chemical cleaning or replacement. Don’t trust the pressure gauge alone. A partially plugged filter that’s channeling shows low pressure differential but still passes dirty water.

Pressure Test Zone by Zone

Close all zone valves except one. Turn the water on slowly and watch the gauge. The system should reach operating pressure in 10 to 15 seconds and hold steady. If pressure creeps up over 30 to 60 seconds, you’ve got partially plugged emitters restricting flow. If pressure drops, you’ve got a leak.

Walk the zone while it’s pressurized. Mark every geyser, misting pinhole, and emitter that drips instead of streams. Fix them before moving to the next zone.

A pressure regulator stuck open because the internal diaphragm dried out and cracked over winter will over-pressurize an entire zone. Emitters rated for 15 PSI running at 40 PSI blow out. Flow rate spikes, distribution uniformity tanks, and you won’t see it unless you walk the lines during the test. A new regulator costs $15 to $40. Replacing 300 blown emitters costs a lot more.

Emitter Spot-Checks: Don’t Trust Your Eyes

Pick five emitters per zone, spaced across the full lateral length. Catch the output from each for 30 seconds in a graduated container. At 1 GPH, you should collect 16.9 fluid ounces in 30 seconds. More than 10 percent variation between highest and lowest means something is wrong. Partial clogging, pressure variation, or aging tolerance issues.

This takes 10 minutes per zone but it’s the only way to know your distribution uniformity is still acceptable. Visual inspection is worthless for flow rate. An emitter that looks fine can run at 60 percent of spec.

A University of California study found drip systems lose 3 to 5 percent of distribution uniformity per year without maintenance. After three years, you could be at 85 percent DU, losing 15 percent of your water to uneven coverage. On a 10-acre vegetable operation using 24 acre-inches per season, that’s roughly 98,000 gallons wasted. The water cost is only about $25. The yield loss from drought-stressed patches is where the real money disappears.

Fertigation System: Prime and Calibrate

If you inject fertilizer through your drip system, the injector needs attention before the first feeding. Venturi injectors pick up mineral deposits during the off-season. Pull the suction line, flush it with clean water, and check the orifice for scale. A partially plugged venturi changes your injection ratio and you’ll feed at the wrong rate for weeks before you notice.

Dosatron and electric metering pumps need a calibration run with plain water. Fill the stock tank with a known volume, run for a timed interval, and measure what’s left. If a Dosatron rated at 1:100 is actually pulling at 1:140 because the piston seals dried out over winter, you’re underfeeding by nearly 30 percent. The first fertigation of the season sets the tone for early crop development. Getting the ratio wrong in April shows up as stunted plants in May that never catch up.

Calibration takes 20 minutes. A Dosatron seal kit is $30 to $60. The yield penalty from four weeks of underfeeding is invisible. You just harvest less and chalk it up to a bad year.

The Startup Checklist

Do it in this order:

1. Inspect pump and water source. Run to waste. Fix problems. 2. Walk all above-ground lines. Mark cracks, splits, animal damage. 3. Flush every lateral and submain to waste before the filters. 4. Clean or replace filter elements. 5. Pressure-test zone by zone. Walk each zone while pressurized. Fix leaks. 6. Spot-check five emitters per zone for flow rate. 7. Prime and calibrate fertilizer injector.

That’s a half day for a 5-acre system, a full day for 20 acres. The parts for the fixes you’ll find cost $50 to $200 total on a typical year. The cost of skipping this routine is a season of uneven irrigation, lower yield, and emergency repairs in July when it’s 95 degrees and you’re already behind. I’d rather spend the half day in April.