Drip Irrigation Run Time: Turning Gallons into Timer Hours

"My beds need an inch" is not a timer setting. Emitter flow, spacing, and hours are. Multiply the first two and you get gallons per hour on the bed. Divide the gallons in that inch by that rate and you get the run.

The drip tool sizes the zone so the last emitter still has pressure. Tape stays above 8 psi. Keep flow under 5 feet a second. One zone at a time is the normal day. Everything at once is the stress test. Run time is the other half: how long that zone stays open.

The inch, in gallons

Salanova Butterhead on a 30-inch bed wants 1 inch a week. Two drip lines. Emitters at 8 inches. Each emitter is 0.42 gallons per hour. The sheet rates that bed at 63 gallons per hour per 50 feet, and 77.9 gallons per week per 50 feet for the inch.

Bolero Nantes is the same tape geometry. Two lines. 8-inch emitters. 0.42 gallons per hour. Same 63 gallons per hour per 50 feet. Weekly water is 0.9 inch, which the sheet puts at 70.1 gallons per 50 feet. The tape did not change. The crop did.

Sun Gold is a different tape. One line. Emitters at 12 inches. 0.5 gallons per hour. 25 gallons per hour per 50 feet. Weekly water is 1.5 inches, 116.9 gallons per 50 feet. Do not time a tomato zone with a lettuce rate.

Hours on the timer

Emitter flow times emitters per foot times hours is the gallons you applied. Spacing sets the emitter count. On the Salanova bed, emitters sit every 8 inches, so each line has 1.5 emitters per foot. Two lines make 3 emitters per bed-foot. At 0.42 gallons per hour that is 1.26 gallons per hour per bed-foot, which is the sheet's 63 gallons per hour on 50 feet. The spacing is already in the rate. You do not add it again.

Run time is gallons needed divided by gallons per hour.

For the Salanova inch on 50 feet, 77.9 gallons divided by 63 gallons per hour is 1.24 hours. That is about 74 minutes. The sheet prints the gallons and the gallons per hour. It does not print the timer. The division is the timer.

For the Bolero 0.9 inch on 50 feet, 70.1 divided by 63 is 1.11 hours. Same tape, shorter set, because the crop asked for less water.

A 4-bed lettuce zone on the drip board is 600 emitters and 4.2 gallons per minute. A 1-bed carrot zone is 150 emitters and 1.05 gallons per minute. Open one zone. Set the hours from that zone's crop sheet. Do not average them.

Deep set, not a daily sip

The target on these sheets is a weekly inch, or 0.9, or 1.5, applied as a set. It is not seven short runs. A daily sip wets the top and leaves the root zone short. The 77.9 gallons is the inch. Split it into seven visits and you have watered the surface seven times and applied the same total only if every visit actually ran. Most timers set that way never reach the total. The bed looks wet at noon. The crop is short by Friday.

Header loss and velocity are the other failure. The board flags a zone that wants a larger header, and it holds header loss under 3 psi. A perfect run time on a zone that is below 8 psi at the last emitter is not an inch. It is a short bed and a dry far end. Size the zone first. Then set the hours from the crop's gallons.

Read the weekly inches and the gallons per hour off the cultivar. Divide. That is the run.