A special for those who like to obsess about details and numbers…and gardens.
So, reticulation: I was hoping to avoid it, but…well, this is Western Australia, very hot, dry summers. I’ve used only Western Australian plants, so the idea is they should be quite happy. However, a number of factors have driven me to install a retic system:
1. I keep reading that while Australian plants will survive without added water and nutrients (more on the “Great Fertiliser Scandal” another time), they don’t thrive. To quote the sage (John W. Wrigley):
“Many plants we see in the bush are, however, growing sub-optimally. They may be stunted, flower production may be poor or foliage may be sparse. In gardens we expect to grow a plant so that it is at its best.” From Australian Native Plants by John W. Wrigley and Murray Fagg, 6th Ed, page 59.
And I really want the garden to be at it’s best for when we go traveling in May and, longer term, I want it to look stunning for when we come to sell in a few years time.
2. The front garden is clearly stressed (take a look at the pictures of acacia rostellifera below). I’m not entirely sure why, but it seems reasonable to assume that the two mammoth Agonis Flexuosa (“WA Peppermint”) and two palms (how I wish I’d cut you down a year ago) are sucking up the water and nutrients.
3. I’m about to launch a third wave of planting and won’t be here to nurse the new plants through next summer’s onslaught and I’m really not sure I can ask a tenant to spend the hours needed to hand water effectively.
Thus, retic has arrived.
Given how prolific retic is in WA I expected it to be easy, but then, the Devil’s in the Detail and I’m a perfectionist and a tight-wad. I’ve been a bit surprised by how little decent information there is out there. I skimmed a number of library books, but they all turned out to be a bit “fluffy” and not much use at all when it comes to details; in fact their default position seems to be “pay someone to do it”. That’s no use!
Hence, I figured it out as I went along and here are some of the details:
A Case Study in Retic Installation
Site
A front garden. About 200 m2 of south facing, road bordering, sandy soil, heavily mulched with “raw” (in the sense of “rough and ready”) woodchip. Minimal soil improvements: compost at planting, light feeding with an organic fertiliser once. (No Bentonite clay added, on reflection it might have been a good idea.)
Around fifty WA natives were planted last June and October. I have plans for another twenty five’ish plants in May this year. Two very mature Agonis Flexuosa, south side, front and centre. Two evil palm trees, reasonably mature, east side. We did have some straggly grass, which became the victim of chemical and trench warfare May/June last year.
The plants seem underdeveloped compared to their compatriots in the back garden where the competing trees (all exotics) and were eliminated over winter last year. That said, the neighbours over the back fence have a couple of huge palm trees right on the boundary and they don’t seem to be affecting our back garden too much.
Materials (full list with prices in the spreadsheet available on request…I can’t work out how to attach it)
I’ve gone for 13mm poly pipe running off the garden tap at the front. I’ve used about 85 m of pipe and 57 drippers (standard Pope “Easy Clean” drippers designed to deliver 4l/hour).
The pipe is assembled as follows:
- From the tap to pipe there is a timer, an in-line filter and a pressure reducer. Then there’s a run of about 8 m to the centre of the garden, from which there are three branches made up of three T pieces.
- Each branch consists of a loop (note: Loop, not straight lines). The loops are about 32 m (Front verge and main screen), 18 m (round the palms) and 21 m (inner screen and in front of windows).
- Each loop includes a tap mid way along it.
- Most of the drippers are inserted directly into the poly-pipe. I used a 3 mm drill bit on a cordless drill to make the holes (!). A few drippers run off 4 mm hose attached by 4 mm screw thread joiners.
Design points
Because detailed information was so sparse, I made the system up as I went along. It may be sub-optimal, but seems to work fine. Some points:
- The “In-line filter and pressure reduction” piece went in because when I connected the system straight to the tap it sprayed water from all sorts of places: the pressure was too high. I had read that drip systems need between 100 and 150 KPa (Kilopascals, a unit for measuring pressure) of pressure, but nobody mentioned what the mains pressure out of the tap is likely to be: clearly it’s a lot more than 150 KPa.
- I never even entertained the idea of cutting into the mains and running a solonoid/auto controller-box-thing system off that. Those systems seem to be for people who love lawns, and don’t mind seeing water flying everywhere and running down the gutter.
- I went for drippers rather than drip-line (“drip-line” being the hosing that has little holes in it every 30 cm or so, so it drips along it’s entire length) because I wanted to make sure that water went to each and every plant in the front. I wanted that because the whole area looks so stressed I was concerned a drip line might miss some bits. However, I’m considering a drip line for the back because it looks easier to install, costs a bit less and the garden is a lot healthier looking overall.
- I went for loops rather than straight runs for consistent flow across the system. I read in one book (no idea which one now), that the usual maximum length of a drip-line is 50 m. Any more than that and the ends get less water. Apparently if the same line is run in a loop, it’s effective length is 100 m, which makes sense. Anyway, I thought that what’s true for drip-line would also stand for drippers. Hence I used loops in the hope it will result in a more consistent flow across the system. This appears to be true, although I’ve not measured the performance of individual drippers along the line (yet!).
- Each loop includes a tap for flushing purposes, so the line can be cleaned.
- I ran the line from the tap to the middle of the garden and then to the three loops to try and ensure the water was evenly distributed across the three loops. On reflection, the water pressure and flow seems more than adequate for the number of drippers, so this feature may be redundant.
Installation
(I’m beginning to understand why most people’s words on drip irrigation are so lacking in detail…!)
Frankly: I should have put the retic in before putting down the two truckloads of wood chip out front. C’est la vie. Hence, I spent a happy few hours in thirty plus degree heat digging channels in the wood chip, laying pipe and then covering them back over. I found the best method was to use a “grubber” (aka “pick”? Like a hoe, but more robust) to break up the packed wood chip a bit and then used my hands (gloved, it’s spiky wood-chip) to clear the channels.
I found the poly pipe a total bastard to work with (excuse me) because it kept re-coiling. I eventually found that I could get it to lay flat by laying out a length of about 6 m and then twisting the remaining coil against the natural turn to get the twist out…good Lord, that makes about as much sense as the Tax Code. Swearing helped too.
I used clips on all joins in the poly pipe (of course).
The cordless drill was a God-send. As were the garden secatuers I used to cut the pipe with.
Performance
I love my water meter. I ran the fully assembled system for an hour the evening it was finished. It consumed 300 litres (exactly!). Over the 57 drippers, that’s about 5.3 litres per dripper, slightly more than the design specification of 4 litres per hour. I’m not sure why that is, but I hope it’s going to be OK. It doesn’t speak of any huge leaks anyway.
That result was reproduced on a two hour run yesterday…I’m beginning to realise how tempting it is to over-water with retic in place!
More importantly, it suggests that the system could happily carry more drippers, which is good news because I’m about to plant another 25 or so plants, and each will have its own dripper.
And, I want to see if I can extend the system to the back and run both the front and back off the one tap… coming soon!
Financials
I have a spreadsheet…a very detailed spreadsheet it is too. In the unlikely event anyone is reading this bit and is similarly obsessed I’ll email to you if you want (just use the comments to ask). Anyway, some points:
Total spend = $203.76 (That’s Australian $’s).
Cost of components actually used = $142.79 (I have quite a number of straight 13 mm joiners, 13 mm and 4 mm pipe, and a large number of drippers left over.)
Waste as a %’ge of total spend = 30% (Bad! Some is in unopened packets and so is returnable. Also, I’m hoping to get the figure down when I install the back garden system and use up some of the left-over bits.)
Overall, $142.79 is pretty good for a fully installed drip irrigation system, certainly better than the thousand or so I’d have probably shelled out if I’d followed The Books’ advice and brought in a professional.
Finally: sadly, I worked out and plotted the unit cost of drippers in different pack sizes. I wonder if anyone else gets the same sense of satisfaction from knowing that the unit cost of Pope’s drippers follows a very nice exponential curve from the bag of 10 to the bag of 25 to the family pack sized bag of 50. Here’s the graph to prove it:
Anyway, on that bombshell…
Mandurah Native Gardens 
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