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Watering on the Cheap

Initially the pots were packed cheek by jowl. Why not. The pots were 6" across, the trees from tip to tip were only half of that. At the end of the third year however they were overlapping. By the end of the fourth, the lower branches were starting to look sickly from lack of light.

Easy enough: I'd heard of pot in pot. I did a variation on it, pot in ground or PIG. This sort of works. See separate article. (PIG pot system) However, I could no longer water them with a lawn sprinkler and get a reasonable fraction of the water into the pots. So I was back to watering by hand.

With only 600 pots set up this way, it took nearly two hours to water them, two hours I couldn't spare from all the other chores. Worse, in a significant number of pots the dirt ball shrunk away from the pot, so that most of the water bypassed the tree. (See article Drainage -- too much or too little.)

I took various steps to try to defeat that, all time consuming. I needed a way to water these trees slowly enough for the water to soak in.

I was ordering drip pipe for another chunk of the nursury, but the PIG pots weren't on an even spacing. (Really hard to drive a tractor and put down an auger in exactly the right place.) On the average they were 30 inches apart. Most of them were within 2" of this. But enough were off that I couldn't just order two thousand feet of drip pipe with 30" spacing.

The other alternative were drippers. But they were a buck each. (Ok, ordering a thousand of them probably 70 cents each...) And from all accounts they were fussy to maintain.

Back to the drawing board.

I had a thousand feet of 1/2" utility grade black poly pipe from my initial pipe run to the pot yard. Much experimenting with making holes. I wanted a hole that was small enough that several hundred of them wouldn't create huge pressure losses from one end of the pipe to the other. Since my supply at the pot yard was about 20 litres per minute (5 gpm for metrically challenged.) and I wanted to water an entire block of 300 trees at a time, each hole could only deliver about two litres per hour. (5 gpm = 300 gph = 1 gal/tree/hr = 4 liters per tree per hour, but delivered at that rate would result in zero pressure at the end. By cutting this in half, I figured that I would get close enough to even distribution. It helps that the PIG blocks run downhill from the source, so that gravity makes up for some of the pressure loss.)

The best hole was made with a sewing needle, refered to as a sharp (very small eye) put in a cordless drill.

At the top of the PIG block I split the source into a pipe for each row, stretched the pipe snug so that it would wander less with changing temperatures.

The bottom end of each pipe had a valve. This to allow draining the pipe for winter, and to flush junk from the pipe.

Pressurize the system, check for leaks. Open the valves at the bottom for 10 minutes each to put the full violence of the system scouring the inner walls. (Hah! On a good day I get 35 PSI at the pot yard.)

Drilling the holes is fairly fast. They are off centre from the top, drilled so they spray into the lower branches of the tree. Sometimes I miss. Those get a small rag tied over the hole.

Since the row of pots isn't quite straight. (My auger placement wanders in direction as well as distance.) occasionally the pipe isn't over the pot. Stuffing a twig into the corner of the pot secures the pipe.

Junctions.

There is a need to make connections. I found that the plastic splices for 1/2 pipe have a hole only about 5/16 in diameter. Serious pressure loss. However 1/2" copper pipe works great for joints. Cut a piece about 6" long, rough up the surface with sand paper, and force the copper into the poly. I usually mark the centre of the copper pipe so that I can judge which end needs to go in further.

So far I have been unable to pull these apart. I suspect they act like Chinese finger cuffs -- putting the poly in tension make it grip the copper pipe even more tightly.

And this method is cheap. (I have a bucket of copper pipe scraps.)

Anchoring the ends.

It's important to keep the pipe from drifting. To do this, I put in under enough tension to stretch it about 1/2 of 1%. (About a foot in a 200' run.) This takes about 40 lbs force to do.

I didn't trust the plastic tees to take this kind of load. Either the T would break, or the pipe would slide off the end. I took a 6" x 1" x 1.5" block of wood, drilled a 3/4" hole in it, then cut the wood through the hole, so I had two blocks with half a hole. (I have a band saw -- working with small blocks is reasonable. If you make these on a table saw, drill your holes and rip the board, before you cut them into 6" blocks.
Also with a table saw you will probably have to use a 13/16 or 7/8 bit because of the wider kerf.)

A pair of these blocks are fastened around the pipe with 1/4" bolts with washers on either side of the wood. Then that block is attached to a stake.

If you are using this method for shelterbelts, you can probably do 600-1000 feet at one hole every 8 feet with half inch line. If you want to do 2000 feet, the first 1000 should be 3/4" pipe.

Remember that as you get further from your source, you have less pressure working for you. Hills can make this a lot worse.
2 feet of elevation difference is roughly 1 psi.
You want the hills to either work for you, or to be small in comparison to everything else.

You want the pressure to be at least 5 x H where H is the height variation in feet along the pipe. So if you have 10 feet height variation, you want 50 psi. This will mean that the pressure differences caused by the height are only 10% of the total pressure, so the difference in flow is small.

You can fudge this if you run your pipes downhill. Gravity then makes up for part of the pressure loss from the pinhole leaks you put in.

Checking the pressure.

An easy way to get an approximate check on the pressure is to see how high the spray goes. Bend a tree to one side, and then find the top of the stream. On my first run of pipe I found that it was about 5' at the top end, and nearly 6 at the bottom end, gravity more than making up for the water loss.

(The height of the spray depends on the velocity the water comes out of the hole, which in turn depends on the pressure.
This method of 'measuring' depends on the holes being the same size, and ignores air resistance. )

If you need a more accurate check on your system, take out a bunch of tin cans, and distribute them under various holes, and run the system for an hour.

Breaking News

Firstly, I've given up on trying to keep the holes pointed up. Not only does black poly pipe stretch when it changes temperature, it also twists. Arg. As a first approximation, I disconnected the wooden blocks from their stakes, and turn the pipe over. This got most of the sprays back into the pot. However some were perverse. For those I cut 5" squares of old tarp, and stapled them around the pipe with the pipe along the diagonal, so that the water would drip into the pot. A plier stapler (any office supply store) is easier than an desk stapler.

Secondly: The holes plug, exactly what I was worrying about with commercial drippers. I found that a needle in a pair of vicegrips works well for punching holes, but it still meant I had to go to each tree, kneel down, fumble through the lower branches of the tree, grab the pipe, position the needle, and OUCH @#&(& I just put another hole in my thumb.

Oh well. My mistake didn't cost me a buck each.

I'm not sure if the hole is oozing shut, or if it is clogging with dirt. I found that holding a needle in a pair of vice-grips works as well as a drill. Anyway, I re-punched one block, using a larger needle. Now the holes are large enough that I can only do the one block at a time. Back to the drawing board.