All plants need a certain amount of water to grow. One of the biggest decisions that home gardeners needs to make is how they plan to get the water to the plants that require it. Simple systems such as a trigger nozzle on the end of the hose can be the most efficient but do take up a lot of time especially for large gardens. Large automated systems work well but are more expensive to set up and can become inefficient if incorrectly installed. Considering all the options available ensures that you will get the best system suited to your lifestyle and needs.
Designing the garden with irrigation in mind helps to save lots of water. Try to plant garden beds out with plants that have similar watering needs and position the beds so that drought tolerant plants are in the drier areas of the garden. If you do want more high water requiring species try to locate these in areas that naturally remain wetter over the year.
Step 1: Make A Plan Of The Area To Be Watered
On a sheet of graph paper sketch all buildings and paths on your block. All garden beds should then be drawn in and labelled accordingly. Any obstacles such as trees, fences and garden furniture should be shown, as well as the location of all taps and the water meter.
Step 2: Calculate The Water Supply
The water flow rate is very easily measured using a household bucket (9 litres) and a stopwatch. All taps and household appliances should be turned off. Turn on the tap closest to the water meter to its maximum flow and slide the bucket underneath. Time how long the bucket takes to fill. To convert this into litres per minute divide the time taken (seconds) into 60, then multiply by 9.
Example: If the bucket takes 10 seconds to fill… 60/10 x 9 = 54 litres per minute.
This procedure should be repeated for all taps that are likely to be used as a water source for the irrigation system.
Step 3: Selecting The System
Drippers can decreases the amount of water used by up to 60% compared to sprayer style systems. Drippers water directly to the root system, decrease weed growth and help in the prevention of fungal attack of your pants. Drippers are more aesthetically pleasing than sprayers as they are buried under mulch, they also don’t need the constant adjustments that sprayers require when plants grow and block their trajectory.
Microsprays are generally an inefficient method of watering gardens. This system is severely effected by any slight breezes and needs constant attention as the plants in the garden beds increase in size and block the spray. The fine spray can also create fungal problems on the leaves of the plants. Microsprays work best in situations where the plants require the humidity created by the sprayer as in a fernery or tropical style garden with bromeliads.
Pop-up sprinklers are normally used for lawns. Most pop-up sprinklers have some form of radius and arc adjustment that makes it quite easy to water almost any shaped area. These sprinklers use large amounts of water so it is important to check your water supply accurately before installing them. Always use 19mm poly pipe for pop-up sprinklers.
Step 4: Designing The System
Group beds together by the amount of water that the plants require into high, medium and low. An example of an appropriate watering schedule over a week using 2 litre per hour (LPH) drippers at the recommended spacing is shown below. The duration needs to be altered depending on the weather conditions, during cooler weather plants require less water while during the warmer periods it may be necessary to increase the watering duration.
|Flowers / Vegetables||1 hour|
|Small Trees / Shrubs||1.5 hours|
|Medium Trees / Shrubs||2 hours|
|Large Trees / Shrubs||3 hours|
The water from each emitter spreads out and down into the soil. Depending on the soil type the water can spread up to one metre from each dripper. When laying drip irrigation in garden beds your soil type determines the optimal distance between drippers.
Clay soil – dripline spacing 50-100cm
Loam soil – dripline spacing 40-100cm
Sandy soil – dripline spacing 30-100cm
These spacings ensure that all the soil along the line receives water, if your plants are not closely planted together it may be possible to decrease the number of drippers so that they are concentrated where the water is required.
Dripline is best laid in either a grid or loop pattern depending on the shape of the garden bed. Looping the dripline back onto itself helps to maintain similar pressure over the entire line. If the dripline runs are longer than 50 metres or over undulating terrain it is best to use pressure compensated (PC) drippers that ensure that the same amount over water is distributed across the entire length.
Garden Bed Arrangement
The dripline should be placed between the soil and the mulch layer to prevent any evaporation and ensure that the water travels directly to the root zone. This layout works well in odd shaped garden beds or when the plants are not planted closely together.
Drip System Accessories
Flusher valves should be used at the end of lines to remove any grit that may enter the system. The valves begin open when the system is activated and then shut of after a couple of minutes.
Vacuum breakers are placed at the highest point along the system and stop the drippers from syphoning dirt and mud into the line when it is switched off.
Pressure reducers may be necessary in areas of high pressure. Install these at the start of the line before the drippers. Automated systems may require the solenoids to be turned down, on manual systems simply turn down the tap.
In-line filters should be installed at the start of the irrigation line to remove any dirt or debris before it enters the system.
Converting an existing spray system
There are a number of methods to convert your existing spray system to a drip system. Female threaded 13 mm elbows and tees or 4 mm Micro tubing can be run off risers but it is preferred to plug or remove all risers and run the tubing off the poly piping. Dripline can be cut into the poly pipe before the first sprayer, you can then either remove the unused poly pipe or simply remove the risers. If the system operates over a number of garden beds the dripline can be reconnected into the poly tube where it runs to the next section.
Turfed areas require a large amount of water to look their best and in many places across Australia it is illegal to use mains water to irrigate lawns. Although dripline can help limit the amount of water required and decrease disease problems it is still recommended to remove lawn areas wherever possible. Laying dripline subsurface of a lawn may result in some root intrusion of the drippers. If this does occur it may be difficult to remove the effected parts of the system without having to remove large sections of lawn.
Gear Driven pop-up sprays when used for lawns and produce larger droplets than micro spray systems. Gear driven sprays do use large amounts of water so make sure that the pressure at each spray head is adequate to allow for the system to operate correctly. Overlapping sprays ensures that all the areas of the lawn receive water eliminating dry spots.
Step 5: Installation Hints
Before digging any trenches it is a good idea to check with local authorities for the positioning of Telstra, Melbourne Water, electricity and any other services as it is a very expensive mistake to dig through these services. The main tools required will be a mattock, a straight edged shovel and a trenching shovel. Using some sort of stake, mark in the position of all sprinklers.
It is easiest to dig all the trenches before laying out any pipes. Keeping the trenches as straight as possible dig the trenches approximately 150mm-200mm deep. When trenching through a lawn make a ‘V’ in ground about 150mm wide at the top. A neat sod should then be able to be lifted at and be replaced in exactly the same position once the sprinklers are in place.
Once the trenches have been dug check them for stones which may damage the pipe. When you are satisfied that the trenches are clean the pipe can be layed out. Place the pipe in the trenches, cutting it roughly to size. It may be necessary to backfill small sections or use bricks to hold poly pipe down. When the pipe is all in place connect in any fittings such as elbows and tees.
Once installed remove the flusher caps at the end of the drip lines and turn the system on to remove any dirt that may be in the pipes. Sprinklers should also be flushed with their nozzles removed. Prior to backfilling turn the system on and test for leaks, this is also the best time to make any fine adjustments where required.
Step 6: Maintenance
Update when needed, an irrigation system is not a static object and should be altered and changed to suit your garden as it evolves, when you change a garden bed around the irrigation system should similarly be changed. Keep an eye out for leaks and blown sprinklers, go out every now and again and make sure that system is working efficiently and is getting the water where it is needed rather than on the paths.
If you have an automated system change it for each season so that you are not over-watering in winter and under-watering in summer. Install a rain sensor so that the irrigation system does not turn on in the rain. Keep an eye on the weather forecast and turn the system off when rains are due in the following days. Some automated systems can be programmed to remain off for a certain number of days after a rain episode, if you have one of these types of controllers use this function, if you don’t simply turn the system off manually for a few days after rain.