We have a drip irrigation system in place that runs primarily from mains water this year but can easily be switched to the two rainwater tanks in the front garden. That gives us 1800 litres to play with if the mains is cut off. . These tanks are connected to the tanks at the back of the house too so that, if the front tanks runs dry, we can use them instead.
Until this year (2020) the system has run from the rain tanks. This year, however, because of increasing insecurity around water, we are currently running it from mains water. I’m keeping the tank water in case we end up with water restrictions. As Summer eases up, I’ll switch it back to tank water so we can refill them when the rains come.
Drip irrigation is my favourite method. Beside the fact that one can spend forever playing with slight changes and adjustments, it is a really efficient way to water our our perennial garden.
Drip irrigation is a very simple thing but it can be as much fun to tweak an existing system as it can be to create a new one. I’m always on the lookout for ways to make ours just that little bit more efficient. It’s a bit of an obsession really.
Drip irrigation generally runs from black Polypipe or brown poly with holes already set in it at particular spaces. the usual gardening sizes are 4 mm, 13 mm. 19 mm, 25 mm. For now, we will talk only about the most common two sizes – 13 and 19 mm.
Components of a drip system
Pipe comes in 25 or 50 metre rolls for 19 and 25 mm pipe. Of course, you can buy it in much longer lengths but these are the usual sizes that you will buy from a hardware store or garden centre.
The pipe connects to another hose or a tap via special fittings. There’s a few different designs of those.
Once you have the pipe, there are lots of options for configuring it just the way you want it. Usually, it will be cut into straight lengths, some of which will be joined at angles or to make loops. Most of the items listed below are ‘barbed’ that means that where the piece slips into the pipe, there is a barb that the pipe squeezes over, ensuring a pretty good fit.
Drippers are the what its all about. They reduce the flow rate of the water in the pipe and let it drip out. They are usually rated as litres per hour (lph) at 100 kPa (kilo Pascals but they may be in pounds per square inch in some countries). Common rates are 2, 4 and 8 litres per hour.
I favour adjustable drippers that flow at 0 – 50 lph. Adjustable are better in my books because, beside adjusting the flow according to the season and customizing it to a plant, you can close off individual drippers should (heaven forbid) a plant dies.
Drippers are put through the walls of the polypipe in two ways. There is a punch available that punches the right sized hole through the pipe. Then there are two styles of connection – a barbed one that you just press into the hole until it snaps in or a screw one that you screw into the hole until the dripper is snug against the pipe. I prefer the screw ones.
You can get easy clean drippers too that you can take apart to clean out. There’s a paragraph on maintenance later where I’ll go into more detail on that.
Joiners come in a few varieties. There are straight joiners for joining 2 lengths of pipe together. There’s T pieces for joining 2 pieces at right angles to another. Then there’s cross pieces for joining 4 pieces to a central point.
Filters are a must and they come is different sizes but all do the same job – keeping debris out of the pipes.
Pressure reduction valves
Pressure reduction valves are handy if you have very high water pressure. They are designed to let a certain pressure of water flow and vent any extra through a hole in their side. The usual pressures that you can buy are 100, 200 and 300 kPa (kilo Pascals). Most drippers are rated as flow rate (litres per hour) at a certain kPa. The ones I use are 0=50 lph at 100 kPa. Others I’ve used are 2 lph at 100.
Inline taps are available for giving finer control to the flow rate in each section of your system. You can use them to close off whole sections or reduce the flow to all components of that section.
Clips. Essential on higher pressure systems or those that are in full Sun (polypipe is plastic and gets soft in the heat), plastic clips fit around the pipe after barbed section of the joiner to hold the pipe and joiner tight. They work on a ratchet and as you press them together, you will hear the ratchet click.
End pieces are for when you reach the end of the line. Unless you are making loops or squares, one of these squeezes into the pipe at one end. A clip will hold it tight and make sure it doesn’t pop out under pressure.
Hot water is a must of you’re doing more than a couple of pieces. Submerging the end of the pipe to be joined in hot water softens it and makes the whole process much easier. It also makes joiners easier to remove.
Size adapters are available to adapt between the three common sizes of polypipe and fittings, I have a couple of 19 mm to 13 mm adapters in our system. I use t-pieces that fit the 19 mm with the third ‘leg’ being 13 mm.You adapt from 13 or 19 mm to 4 mm with a snap in or screw in adapter.
Goof plugs.Everyone makes mistakes or changes their minds or both. When you remove a dripper or some adapters, they leave a hole in the pipe. Squeeze a goof plug into it and you’re as good as new.
Sometimes clips will get stressed, knocked about or otherwise damaged. It pays to check visually check them. If you don’t and your system has high water pressure, the pipe could pop off a joiner and waste a lot of water.
Filters simply unscrew at the top. Then you can slide out the plastic mesh insert and give it a rinse. Filters positioned where a system joins mains water rarely need cleaning but those in between sections on the ground can pick up a lot of debris (especially if you keep forgetting and burying them like I do)mand should be checked quarterly.
Drippers can be taken apart and cleaned. There are ‘easy clean’ versions of most sized with a top the just screws off for a rinse .Other varieties let you screw off the top but there is a solid or perforated rubber or plastic disc inside that you must be careful not to lose. This just pops out of the dripper and you can give it a quick rinse.
The most common cause of debris in the system is a simple one. Because the drippers are usually on the ground, they get covered in dirt, mulch or compost. Tiny pieces of sediment block the holes and can work their way inside and into the pipe. To unblock the holes, you can give the dripper a rinse with a little water, blow the dirt through or give it a hefty suck. All those techniques work well.
If you have an off the ground system, then you’ll rarely have this problem.
Pressure compensation & balancing
Often when you’re putting in a system, you may find that one section just doesn’t get as much, if any water. Some may get an air lock in them too (you can tell an air lock if you go to a dripper on the affected length of hose and unscrew the head a little. you will hear air come out of the pipe and hopefully water shortly after.
If you have a section not receiving any water ( and you don’t have it closed off by an inline tap) there are three things you can do. First, try turning up the tap pressure. You could find that a small tweak is all it needs. Failing that, join part of that section to another section that has water. This could balance it out. The third option is to loop the furthest point of your system back to near the the start. This enables water to flow through the system is tow directions and will usually balance out any flow problems.
Getting water deeper into the soil
To get good soil penetration, place the dripper so that it drips into a piece of pipe sunk into the ground
Positioning drippers in difficult locations
Sometimes the main pipe isn’t close enough for a dripper to reach a plant (especially if you’re like me and keep adding plants after you’ve put in the dripper system. Placing the dripper on a length of 4 mm pipe with a connector going into the pipe can give you the flexibility you need without redoing whole sections.
Doing this will also allow you to move the dripper from time to time around the area above the roots of bigger plants, This will help roots develop more evenly around the plant.