Top 10 irrigation system problems & solutions

As indigenous landscapers we prefer to not install irrigation for our gardens, and rather rely on rainwater or manual watering of individual plants. But irrigation is useful in certain circumstances, such as newly installed gardens, for lush lawns or thirsty exotics, or for food gardens.

Unfortunately, there are a number of irrigation problems we frequently encounter, and in most cases, they can be traced back to poor design or poor installation, or inferior materials. In this article we'd like to discuss some of the most common problems and give some advice on how to fix them. Please keep in mind that every irrigation system is unique, and there may be valid reasons why a contractor has installed your system the way they have. Use this list as a guide, and as always, we'd welcome your questions and feedback.

Herewith are our top 10 irrigation problems and solutions:

1) Inadequate trenching

Arguably the most common problem we encounter in irrigation installations is inadequate trenching of the pipes. Trenching is the most labour-intensive part of the installation, and is therefore sometimes neglected. Many installations are only trenched to the depth of the pop-ups (usually 20-30 centimetres), because this makes it easier - and cheaper - to join the pop-up to the pipe. Unfortunately, poor trenching can result in pipes frequently being punctured, either by yourself or your gardener. As a general rule – and unless there are extenuating circumstances such as rock or house foundations – pipes should be trenched to a minimum of 400mm below the surface, and pop-ups joined to the pipe via swing-joint risers or flexible pipe:

Not only does this keep the pipes well away from ordinary gardening tools (such as garden forks), but swing-joints allow you to easily adjust the height of the pop-ups in future if the height of the soil changes.

2) Lack of head-to-head design

Perhaps the most common design flaw we see in installations is the lack of head-to-head design, which results in dry spots, overwatering, or underwatering of certain areas of the garden. It's a common misconception that if water from a sprinkler is 'reaching' a particular area, then that area is being watered. But the area covered by a single sprinkler is not watered evenly, because (as of writing) there isn't a sprinkler technology capable of this. In most cases sprinklers put down more water at the head of the sprinkler, resulting in an underground water profile that looks like this:

To create an even precipitation over an area, one needs a second sprinkler, placed at the outer radius of the first. Your underground water profile would then look like this:

This is known as head-to-head, and - provided each sprinkler has the same precipitation rate - creates an even precipitation over that area. Here are two scenarios from a top-down/design perspective for a rectangular section of lawn:

There are some exceptions. If you are watering a narrow strip garden, for example, then you can use strip nozzles instead. Capillary action through the soil in the narrow bed will then create a relatively even underground water profile. Likewise, if you are watering shrubs against a wall, you can use sprinklers that reach double the distance. Water droplets will then hit the foliage and trickle down, helping to even out the underground water profile.

3) Incorrect pipe sizes

Another common problem is incorrect pipe sizes - specifically pipes that are too narrow for the distance required. When water flows through a pipe a certain amount of pressure is lost due to friction (known as 'friction loss'). Factors affecting this include the diameter of the pipe, the length of the pipe, and the rate of flow (litres/min), amongst others. (Fittings, roughness of the pipe, and water temperature are also factors). Unfortunately, all too frequently, we see narrow pipes - usually 20mm LDPE pipe - used over too long a distance, resulting in a loss of pressure to the sprinklers. All sprinklers have a specific pressure rating at which they work most efficiently, and a loss of pressure degrades their performance and reduces their area of coverage. Additionally gear drives (rotors) require sufficient pressure in order to rotate, and may stop turning if the pressure in your system is too low. Calculating friction losses requires a friction chart or online calculator, but is an important step in the design of a system. If you currently have pressure related problems due to incorrect pipe sizes, you could try switching to nozzles that use less water (i.e have lower flow rates), or using a stronger pump (if you have a pumped system). Ideally though, pipes should be sized correctly to begin with, so removing old pipes and replacing them with new ones is the most appropriate solution.

4) Poor quality cabling

Comms cables such as these on the right can cause electrical problems on your system and could void your manufacturer's warranty

Automated irrigation systems make use of solenoid valves, which open and close to release water to your pipes and sprinklers. Power to the solenoid coils is supplied from the controller through cabling, with each station having its own cable and a shared common wire. Unfortunately, some systems are installed using inferior cabling, most frequently communications (comms) cables, which are not suitable for underground use.

Comms cables used on this system were left unprotected and exposed to moisture in the irrigation box. Apart from breaking easily, they shorted one of the solenoid coils, requiring replacement and repair

These cables can cause problems with irrigation systems, including shorting of coils or even shorting of a controller. In some cases, manufacturers may void the warranty if it is found that communication cables were used on a system where their controller has blown. For most systems, 1.0mm GP wire should be used for connections from the controller to the valves, and these cables should be placed in conduit (either 20mm or 25mm PVC or LDPE). Connections at the valves should also be waterproofed, preferably with silicone connectors. Finally, cables should be trenched appropriately, and - where possible - laid in the same trenches as the irrigation pipes, 400mm below ground.

The repaired box - a new coil and 1.omm GP wire in conduit, connected with silicone snaplocks

5) Mixing heads with different precipitation rates and pressure ratings

ABOVE: A Rainbird 12van nozzle with a precipitation rate of 40 mm/hr (square spacing)
BELOW: A Hunter MP2000 nozzle with a precipitation rate of 10 mm/hr (square spacing)

Understanding precipitation rates is one of the most important aspects to irrigation design, but is sometimes neglected, especially when maintenance on an existing system is conducted. Different sprinklers put down water at different precipitation rates, so mixing sprinklers with different precipitation rates can lead to overwatering or underwatering of certain areas of your garden. A 12-foot Rainbird cone nozzle, for example, has a precipitation rate of 40mm/hr (with square spacing). In contrast, a Hunter MP Rotator nozzle has a precipitation rate of 10mm/hr (with square spacing) - i.e. four times less water per hour. It's not difficult to understand then that if you have mixed these two nozzles on the same station, why one area of your garden is getting more water than the other. Additionally, the above two nozzles have different pressure ratings, so running them on the same station is inefficient use of one or the other. Similar problems occur when cone nozzles are mixed with rotors/gear-drives, as gear drives usually have lower precipitation rates. To avoid these problems, it's important to first understand the precipitation rates of each of your sprinklers, and to only use sprinklers with similarly matched precipitation rates and pressure ratings on the same zone.

6) Pipes crimped by tree roots

The roots of an Acacia (=Vachellia) sieberiana (Paperbark) have crimped these irrigation pipes

One of the most common problems in established gardens is the crimping of pipes by tree roots. Sometimes this is due to pipes that have not been trenched correctly, but for the most part it is because the commonly used low-density (LDPE) pipe and fittings are too weak to handle the pressures of a large tree's root system. Sometimes - depending on where in the pipe this problem has occurred - crimped pipes can lead to burst pipes, because there is no longer any release of pressure via the sprinklers.

If you find that one half of your garden's sprinklers is working, but the other half is only trickling water, then this might be the problem. Troubleshooting it can be simple, provided you have access to the pipe on both sides of the tree.

Below is a test we conducted on two LDPE pipes that had been laid in the same trench:

At 2.2bar, the first pipe shows a flow rate of 44.9 litres per minute

At 2.2bar, the second pipe shows a flow rate of only 26.1 litres per minute - a 40% drop in flow rate. As this pipe was in the same trench as the one above, and there were no leaks or flow restrictions at the valves, the problem was traced back to crimping by tree roots

Fortunately repairing a crimped pipe is relatively simple: dig down and find the affected pipe, then cut and replace it. If possible, avoid cutting the offending root and rather divert the new pipe around the root system - your irrigation is there to support the garden, not the other way round!

For new installations the use of hi-density (HDPE) pipe and fittings can mitigate these problems, so although these materials are more expensive, they provide a robust and long-lasting irrigation solution.

7) Overwatering

This Buddleja saligna (False Olive) - showing yellowing of the leaves - was being overwatered by an irrigation system

Overwatering leads to many problems in gardens, and is usually the result of poor irrigation design or incorrect timing/scheduling. We've met homeowners who were watering their gardens twice a day, every day, which was a waste of water and damaging to their plants. Plants that have been overwatered are susceptible to fungus and disease, whilst root systems of trees may remain shallow, thereby compromising their stability. To avoid overwatering your garden it's important to know the required amount of water for your plants per week, and to schedule your system accordingly.

Yellowing lawn is a possible sign of overwatering - here around the sprinkler head

On the highveld, the recommended amount of water for 'thirsty' gardens - that is gardens with large areas of lawn or species with high water requirements - is 25mm per week in summer. This 25mm should be spread evenly over the week, and only on alternate days (e.g. 8mm on Monday/Wednesday/Friday). Knowing your plant's water requirements and the precipitation rates of your sprinklers will help you calculate these figures. In winter, some plants go dormant, and may not require water at all. In these cases, irrigation systems should be set to reduce watering automatically - by using the seasonal adjust settings on the controller - or turned off altogether. Lastly, technologies such as rain sensors can pause irrigation when it is raining, and new controllers can connect to weather forecasts to pause the system if rain is expected.

8) Clogged nozzles & filters

Clogged filters should be removed and cleaned under running water. The pipe can then be flushed, and the nozzle and filter replaced

One of the most important maintenance tasks on an irrigation system is ensuring that the nozzles and filters are clear of dirt and debris. In some cases, especially after a pipe repair, nozzles and filters can become blocked with sand, something that usually occurs at the end of a line. If all the sprinklers in a zone are working fine, but the last one or two are only dribbling water, then the problem might be a clogged filter and dirt in the pipe. To resolve this, remove the head of the nozzle and clean the filter under running water, then run the system for a few seconds with the nozzle removed. This flushes out any remaining debris in the pipe, and the filter and nozzle can then be replaced.

9) Micros requiring constant maintenance

Micro sprinklers are small emitters that are joined to your pipes via micro tubing. They are useful for difficult to reach places - such as potted plants - and are easy to install and use. In most cases they are attached to stakes, which makes them easy to move around. Unfortunately, they are frequently overused, often in places where other - more robust - sprinklers would be more appropriate. Micros require regular maintenance because the stakes are easily moved (often by dogs), and the tubing can easily be punctured by a gardener's fork. The heads may also pop off, or be accidentally removed, resulting in a wastage of water. Micros do have their place, but if you find they are a constant maintenance headache rather consider a more robust solution, such as pop-ups, risers, or drip irrigation, or consider manually watering your potted plants.

10) Dogs chewing sprinkler heads

Dogs are our family, but they can be a real nuisance when they start chewing your sprinklers. The biggest problems tend to occur with risers, which are permanently above ground and therefore easy targets for an energetic dog. Short of taking your dogs for longer walks (to expel that pent-up energy), the easiest solution is to convert your risers to pop-ups, which would then be visible only when your system is running. (Set the system to run in the early morning or late evening when your pets are indoors or asleep). Alternatively, you could switch to galvanised risers and brass fittings, which are more expensive, but which will probably (hopefully!) solve your problem.

Read our article on garden problems and solutions here for more on dogs in the garden