Building a Reliable Automated Irrigation System

A reliable system gets the same feed to the last pot as the first, every time. Ours is a mixed batch tank, a pump sized for flow at working pressure, large PVC, a strainer on the pickup with two parallel 200-mesh filters after the pump, and slow spray stakes at every pot. Runtime comes from a catch test, not from the label.

The parts and what each one does

• Feed. We like a batch tank so we can see stable EC and pH before feeding. Direct-to-plant dosing works too; keep A and B in separate stocks at the same injection rate and check EC and pH after injection and at an emitter while the zone runs. Stock mixing: Mixing stock tanks.
• Mixing order. Into the tank or injector line: Part A, then Part B, then bleach, then RunClean. Never mix concentrated bleach with RunClean; it can release chlorine gas.
• Circulation. A small circulation pump keeps the batch mixed and lets a pH doser work. Skip the air stone in a feed tank; aeration can push pH up.
• Pump and pipe. Choose the pump by its flow at the pressure your outlets need, not maximum PSI or horsepower. Large PVC keeps friction low. Details in Why we use Red Lion pumps and large PVC.
• Filters. A strainer at the reservoir pickup, then two parallel 200-mesh filters after the pump, before the emitters. Keep fine filtration off the pump intake. Check whether a filter is rated in mesh or microns; 200 mesh and 200 microns aren't the same.
• Outlets. Plum spray stakes in suitable layouts. See Spray stakes vs. drippers.
• Control. The pump and valve run on the feeding timer. Don't leave the system pressurized all day.

Size it from the outlets

Zone demand: number of outlets running together × flow per outlet (GPH) ÷ 60 = GPM. Count outlets, not plants. 1,400 outlets at 3.2 GPH is 4,480 GPH, or about 74.7 GPM. Then find a pump that delivers that at your working pressure.

Runtime: the volume you want per pot ÷ the measured flow per minute. An outlet catching 200 mL per minute takes five minutes to deliver one liter. Set the volume itself from runoff: about 25% in coco and peat (How much runoff do you need?).

Measure the flow. Our unregulated setup delivered more than the outlets' rated flow. Catch-test several outlets, including the far end of the line.

Build in ways to notice failure

• Label every tank, stock and line. Put filters where you can service them, with valves and unions, and give each zone a way to flush.
• Route drainage so you can check individual pots.
• Check EC and pH at a running emitter, not just in the tank. The plants only see what comes out of the emitter.
• Walk the room after a feed and check for dry pots. That's how we catch a missed feed, like a disconnected tube.
• Watch the room's humidity history. In our rooms, irrigation often shows up as a humidity rise; a missing rise is a reason to check the system.

The filter catches particles, RunClean handles mineral scale, bleach handles sanitation. None of them replaces checking the outlets.

Fix uneven delivery before changing the timer

Catch near and far outlets for the same run time. One weak outlet: clean or replace it. Whole zone weak: check the filter, valves, pump supply and how many outlets run at once. Adding runtime to cover a blocked outlet overwaters the pots that were already fine. More in When part of a room misses an irrigation.