Author: chogan@directresearch.com

 

What I don’t know about garden irrigation could fill a book.   Or at least a blog post.

And that’s what the next post is about.  All the things I thought I knew about irrigation that were wrong.

That’s probably going to be a lot more interesting than this post.  Here, I describe the irrigation system I just put into place this morning.  But be warned, the actual, currently-functioning drip irrigation system is boring.*    Its basically a hose that drips.

* Not that “plumbing project” and “excitement” are things any sane person wants to see in the same sentence.  Try:   “I had a little excitement fixing the leaky toilet”, or “I was halfway through changing the faucet washer and that’s when all the excitement started”.   I don’t know about you, but for me, “excitement” in that context does not conjure thoughts of pleasant events.

Sure, it’s a high tech hose creating beautifully uniform drips.  I’ll describe it below in excruciating detail.  But it’s basically a hose with little holes in it.  Plus enough other stuff to get water from the outside tap to that hose.

The more interesting piece of this is everything that wouldn’t/couldn’t/didn’t work.  The system I just put in place is nothing like what I started out to do, outlined in Post G22-016.  My original plan did not survive even the most casual brush with reality.  That process is far more interesting than the finished product.  But that’s for a separate post.

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What I did.

Above you see the last bit of my newly-installed drip irrigation system.  The brown hose is 1/2″ drip emitter tubing (a.k.a. dripline).  It has a couple of holes (“emitters”) every foot, carefully constructed to drip one gallon of water per foot per hour, at water pressure of 25 pounds per square inch (PSI).  (For a simple metric-compliant reference, that’s about 1.7 atmospheres).

It’s pinned to the soil with standard steel garden staples (the sort you would use to hold down agricultural cloth or row covers.)  Eventually I’ll cover all that with mulch.

Not seen, that brown “emitter” tubing above connects to solid (no-holes) 1/2″ black distribution tubing.  Irrigation distribution tubing is more-or-less cheap, thin, UV-resistant hose.

Three additional brown drip emitter lines are tee’d off that black tubing, one for each raised garden bed.  That all eventually connects back to the outdoor tap on the back of the house.

All-in, there’s almost 100′ of 1/2″ black distribution tubing now pinned to my lawn, distributing water to four garden beds.  There it connects to pieces of 1/2″ emitter tubing (dripline), which then distributes the water to the soil, one drop at a time.

The furthest end of the system is about about 125 tube-feet from the tap, there’s about 150 feet of emitter tubing total.  All of it appears to be functioning correctly.

There are really no details of construction worth noting.  As constructed, the whole thing just sits on top of the ground, held down by the occasional steel garden staple.  Two 1/2″ emitter tubes, spaced about 2′ apart, seem adequate to water the surface of a 4′ wide raised bed.  The 1/2″ pipes all fit together with fittings made for this exact purpose.  Lay out the tubing, cut it with a knife, slide one end over the fitting as far as it will go, tighten up the locking cap.  That’s it.

Well, maybe there’s one pro tip, but it’s standard advice for anything of this sort:  Tubing, extension cords, rope, and so on.  The tubing comes in a roll.  Unroll the tubing onto the ground, by rotating the coil of tubing about its axis, just as if it were a car tire.  Ideally, pin one end of the tubing to the ground and literally unroll the coil by rolling it on the ground.  Do not uncoil it, that is, do not put the roll of tubing on the ground and pull out what looks like a big, long coil spring made out of tubing.  If you uncoil it, you will almost surely end up kinking the tubing as you handle it, and that is double plus ungood. 

Why:  While it superficially looks the same, unrolling is completely different from uncoiling.  When you uncoil it, each original loop on the roll leaves one rotation along the axis of the tubing.  If you had twenty loops on the original roll, and you uncoil it, sure, it’s laid out in a line, but now it’s as if you’d taken one end of the tubing and given it 20 360-degree twists in a row.   And that high degree of twist along the axis will almost inevitably manifest itself as a kink in the tubing.

Basically, a monkey could do it.  The only tool needed is a knife (or scissors) to cut the tubing.  This took me under two hours this morning, and most of the time was spent maneuvering the emitter tubing around my already-existing plants.  If I’d done this while the beds were still bare, I doubt it would have taken me an hour.

Arguably, shopping for the parts was harder than assembling the system.  In the end, to cover four beds, each maybe 4′ x 25′, I bought/used:

• 200′ of 1/2″ emitter tubing (“dripline”, with weepholes)
• 100′ of 1/2″ distribution tubing (no holes).
• Four figure-of-eight fittings to close the ends of the driplines.
• Three 1/2″ “tee” couplings and one 1/2″ straight coupling to connect the first three and the last driplines to the distribution line.
• One in-line pressure reducer
• One drip irrigation female adapter (to convert the end of the distribution line to garden hose thread).
• Some garden staples.
• Optional:  One charcoal filter (see chloramine, below).

I still need to add a timer.

For what it’s worth, if you go with this form of drip irrigation — using emitter tubing or “dripline” instead of individual water emitters — your main choice is between using 1/4″ and 1/2″ emitter tubing (dripline).  I ended up using 1/2″ emitter tubing, and I am glad that I did.  That’s explained just below.

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A few details worth noting.

Half-inch versus quarter-inch irrigation tubing: Quarter-inch line is tiny.  

Above you see the ends of two pieces of irrigation tubing.  The small stuff is the nominal 1/4″ tubing.  The larger one is the nominal 1/2″ tubing.

If you are like me, you probably heard the terms “quarter-inch” and “half-inch” and just fuzzily thought, oh, that’s about twice as big.  But even in theory, if the internal diameters were as described, the half-inch line would have four times the internal cross-sectional area.  And in practice, it looks like the half-inch line has around eight times the internal cross-sectional area of the quarter-inch line. 

Which, roughly speaking, means that the half-inch line has eight times the water-carrying capacity, or conversely, can carry water eight times as far before the water pressure in the line gets too low to be usable.  The manufacture recommends limiting runs of half-inch dripline to 240′ or less, compared to limiting runs of quarter-inch dripline to 33′ or less.   Or about one-eighth the distance.

That has a lot of benefits.

First, you can cover a garden bed just by running one long piece of 1/2″ emitter line back-and-forth.  That’s less work that cutting and connecting many short pieces of 1/4″ emitter line.  In my case, my 4′ wide garden beds required just one piece of emitter line, twice the length of the bed, run up one side and down the other.  Basically, it’s no different from running a soaker hose up and down the length of the bed.  That means need to make just one cut in the supply line, and insert one “tee” connection to connect the emitter line to the black supply line.

Second, the 1/2″ emitter line also serves to distribute the water, in addition to dripping it into the soil.  This adds considerable flexibility down the road.  It carries enough water that you can easily tap into it.  So, for example, if I now wanted to add some additional emitters in the same garden bed, or add a stretch of 1/4″ drip line, I could just add those directly onto the existing half-inch emitter line.

I see just four downsides to the 1/2″ emitter line.  First, it’s stiff, which makes it harder to install (particular, as here, installing it in beds where the plants are already growing).  Second, it provides a less-even distribution of water.  It appears to come with a minimum emitter spacing of one foot, and emitters that release one gallon per foot per hour, whereas the 1/4″ emitter line is commonly available with emitters spaced every half-foot, emitting a half-gallon per hour.  Third, you have to connect it to the supply line with a tee fitting that costs about $3, whereas the 1/4″ emitter line connects to the supply line with a little push-in “spike” fitting that costs maybe $0.25 each.  Finally, it costs slightly more per foot than the 1/4″ emitter line.

Chloramine filter.

I added a a high-volume activated charcoal filter to remove chloramine from the tap water.  These days, no matter where you live, if you rely on public utilities for your water, chances are that your water is treated with chloramine, not chlorine.  And that makes a big difference to some plants.

Once upon a time we had chlorinated water in the DC area.  They literally used chlorine gas.  And that’s volatile.  Spray that on your garden, or put it in a bucket, give it a little time, and most of the chlorine would simply evaporate right out of the water.

But volatility is a liability if you want to maintain a safe water supply with old pipes.  Now our water is treated with chloramine, not chlorine.  Chloramine is persistent, and does not produce as many by-products as chlorine.  The upshot is, it stays in the water unless you take extreme measures to remove it.

Some plants do not tolerate chloramines well.   In the garden, for example, I find that my peas bleach and die if I water them with straight tap water.  It seems to be immediately toxic to the ground cover “sweet woodruff”.  Many seeds are reported to germinate poorly if watered with water containing chloramine.

So when I water with tap water, I do my best to filter out the chloramine.

It costs a bit, but only a bit, to take this extra step.  The high-throughput charcoal filters like the one linked above are good for somewhere around 10,000 gallons.  At that rate, removing the chloramine adds about $3 per 1000 gallons to the cost of city water.  I currently pay about $17 per 1000 gallons (combined water and sewer rate) for municipal water itself.  So if I’m going to water my garden with city water, chloramine removal only adds modestly to the resulting financial pain.

Pressure regulator.

The manufacturer of this line recommends putting a pressure regulator in-line, to restrict pressure to 25 PSI.  That regulator cost about $10, but it seemed like a good idea to follow the directions despite the cost.  It just screws into the overall assembly using standard hose threads.  So I added one.

I don’t think the strength of the tubing itself is the problem.  It looks to me like the various connectors (tees and such) are a little iffy for high-pressure use.

In any case, given that this was the first time I’d ever done one of these, I figured I ought to follow the manufacturer’s directions.   And that includes putting a pressure regulator in-line.

Other manufacturers use “pressure balance” lines and such.  That struck me as being unnecessarily complicated and possibly prone to clogging.  Here, I have one pressure regulator and large-diameter lines to carry the water.  It’s hard to see what could go wrong with that.

Possible conversion to using raw rain water.

There is some possibility that the large-diameter 1/2″ emitter line could be used with a gravity-fed low-pressure (“rain barrel”) system.  I’m skeptical that would work well, but I see people on YouTube who appear to have functioning irrigation set up that way.  For sure, given the low pressure of a typical rain-barrel system (maybe 1 PSI), there’s a far greater chance that will work over a distance with the larger-diameter emitter tubing compared to the 1/4″ tubing.

The point is that there is some possibility that I could just hook up my rain barrels to the installed system and (slowly) water the garden that way.  Either purely gravity-fed, or using a small submersible pump.

I’m definitely going to have to test that before I declare that works.  At the minimum, that’s going to be a slow process, for sure.  These emitters let out one gallon per hour at 25 PSI pressure.  At somewhere around one PSI, what takes the current tap-water system an hour to deliver should take a gravity-fed system at least a day.

If it will work at all.  Some forms of water distribution simply don’t work at all at such low pressures.  Most timers require at least 10 PSI.  Soaker hoses require 8 to 10 PSI.  And, of course, anything designed to spray water at 25 PSI will only dribble it, at best, at 1 PSI.

Winterization remains a mystery at this point.

I’m pretty sure it’s a bad idea to leave plastic pipes full of water out to freeze over the winter.  And I’m too lazy to bury them.

From what I gather, the emitter lines will take care of themselves, slowly emptying out as long as one emitter on the line is at a low point.  The problem is the black distribution piping, where I have multiple low spots between my various raised garden beds.

Tentatively, I’m planning to hook my shop vac up to one end of the distribution line, open up the ends of the emitter lines,  and let ‘er rip.  Basically, blow the water out of the system at the end of the year.

If that doesn’t work, well, with 1/2″ tubing throughout, this really is no different from a bunch of garden hoses.  I’ll winterize it as I winterize my garden hoses.  Just pull them up, empty the water out as I roll them up, and store my irrigation system in a corner of the garage.