I have 20 trees, and I get by with junk garden hose that I leave in place all season.
Here’s a parts list:
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Vacuum breaker. You need this at the hydrant so that fluid in the hose doesn’t run back out the weep hole there after the hydrant is shut off. This uses hydrant threads female-male.
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Pressure reducer. You need this at the vacuum breaker to step-down the water pressure at the hydrant to 30psi. This uses hydrant threads female-male.
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Quick couplers male-female. I use these on either side of the hose timer, so I can temporarily plug in hose sections for filling the sprayer. Or I can disconnect the timer for filling buckets as the need arises.
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Battery-operated hose timer. This runs water for a maximum of 2-1/2 hours and shuts off automagically.
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Junk garden hose. I use a single run from the first tree to the next to the next to the last. There’s a plug with female hydrant threads at the end of the line, of course.
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Drip emitters. These have small barbs in and out. The in-barb sticks into the garden hose. These are rated at 2gal/hr at 30psi, so they’re good for 5gal over 2-1/2 hours. I use 40 emitters, so the pressure reducer needs to deliver 80gal/hr.
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Punch tool. This makes a hole in the garden hose for the emitter barb. Pressing the emitter barb into the hose mostly forms a water-tight seal against 30psi.
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Drip line. I place two emitters at each tree — one upstream and one downstream. These don’t need to be located exactly because I attach a drip line to the output barb on the emitter and run the drip to the exact place I want. Usually I tape the open end of the drip line to a slit in the plastic mulch.
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Bug excluders. These are strainers placed in the open ends of the drip lines.
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Irrometers. I install a deep one and shallow one under a tree in the middle of the orchard to measure soil moisture. I read them to know how often to start irrigation.
With this setup, irrigation is a matter of starting the hose timer every couple of days or as often as necessary. After that, everything is automatic. I live on a sand dune, but I don’t carry water to my trees.
Because the hose is pressurized during use, the hose can follow small changes in the elevation of the orchard without my worrying too much about overwatering the low-lying bits.
Seasonal maintenance is a matter of unfurling the hose after winter storage, replacing hose washers and quick-coupler gaskets, replacing broken emitters, and replacing missing drip line and bug excluders.
This arrangement would not be suitable for injecting any chemical fertilizer because it’s attached to the potable water supply. The risk of contamination is considerable.