Installing A Micro-Irrigation System

As world climate changes become more pronounced, droughts in many different countries across the globe will become more commonplace. Gardeners can do their bit by installing irrigation systems that not only cut down on water wastage, but also ensure that their plants are getting all the water they need.

A micro-irrigation system, as the name implies, is a small irrigation system. There are two main types that are commonly used in the home garden. These are drip (or trickle) systems and sprinkler systems. Drip systems provide a slow dripping of water in a particular area. Sprinkler systems provide a small jet or spray of water that covers a wider area. Of course there is no reason why you cannot combine the two.

Advantages of Micro-irrigation Systems:

These systems are popular for a number of reasons, such as:
  • They conserve water (making better use of water resources) than conventional hose sprinklers or a regular hose pipe, particularly when delivering water to garden beds, crops or individual trees.
  • They are relatively cheap to install.
  • They are easy to install, only basic hand tools are usually required.
  • They only need relatively low water pressure to operate. This can be a real advantage in areas where water pressure may be a problem, and/or at times of high water demand.
  • A pump can be fitted ahead of the system to increase water pressure if necessary.
  • They can be easily repaired, maintained, or modified to suit changing needs.
  • The pipes and tubes used in such systems are made from low density plastics, and are flexible and easy to hide among rocks and plants. Laterals can be buried and outlets placed in very obscure positions if so desired. If laterals are not buried, the gardener has even greater flexibility in being able to move the position of the outlet if desired.
  • Systems can be automated for greater flexibility. You can simply turn them on, leave them, and they will turn off after a set time, or you can install a programmable controller that will turn your system on and off according to your instructions. This can be very valuable if you are away for extended periods.
  • Both drippers and sprinklers can easily get clogged, but they are also both easily unblocked.

Drip versus Sprinklers

  • They are good for watering individual plants such as potted plants and isolated trees and shrubs.
  • They work better in heavy clay soils where water penetration is slow.
  • The concentrated wetting pattern they provide means they are better on severe slopes (they should located up the slope from the plant) to minimise erosion.
  • They are preferable for plants (e.g. roses) which may suffer from an increased likelihood of fungal diseases if watered from above.
  • They will still work when water pressure is extremely low.
  • They help keep weeds down as there is less damp soil surface for weed seed germination.
Micro-sprays / Sprinklers
Micro sprays can either be spray jets discharging a coarse to fine spray, or sprays which discharge the water in streams or fingers.
Both are suited to:
  • Fitting into any garden shape with a variety of watering patterns and flow rates available.
  • Free draining soils because of the strongly vertical draining patterns of such soils (as apposed to a more horizontal pattern in heavy clay soils).
  • Shallow rooted ornamentals, shrubs and annuals generally.
Micro sprays are better for:
  • Exposed areas subject to wind.
  • Penetrating dense foliage and compact garden beds.
Spray Jets are suited to:
  • Protected areas and shade-houses.
  • Areas requiring a moist microclimate, such as a fernery.
Also available are Misters to increase humidity and Rotor sprays for larger areas.

The Basic Components of a Micro-Irrigation System

A basic system consists of four main components:
  1. Plastic pipe – This is usually flexible black polyethylene pipe. The most common sizes are 19mm diameter, which is used for larger systems as main lines, or more commonly 13mm diameter, which is used for mains and laterals. 4mm diameter micro-tubing is commonly used to connect nozzles to main supply lines. When soaked in very hot water, these pipes become pliable and can be simply pushed over connectors to join them to other sections of pipe or for the 13 & 19mm pipe, to attachments for connecting to a tap. The 13 & 19mm pipes are readily available in rolls of varying sizes, from 20m upwards. The 4mm micro-tubing is readily available in smaller rolls (e.g. 5 or 10m).
  2. Connectors/joiners – These are two way, three way, four way, and elbow joints used to connect sections of pipe together. This category also includes small off-take connectors which are pushed into small holes pierced into the main and lateral supply lines, and then rigid sections of 4mm micro-tubing (risers), or flexible micro-tubing are connected to them.
  3. Clamps – simple plastic clamps that are placed around the pipe over the connectors/joiners in 13 & 19mm pipe, and then closed by squeezing them with a pair of pliers or similar tool so that they lock. This helps ensure the pipes don’t pull apart due to movement or from water pressure.
  4. Outlets – A large variety of usually moulded plastic outlets, which discharge the water either as a spray, a jet, a drip, or bubblers (like a cross between a spray nozzle and a dripper). A hole is simply poked in the pipe wherever you want to discharge water and a nozzle (sprinkler) or dripper is pushed or screwed directly into the hole, in the main supply line, or into micro-tubing attached to the main supply line. Some of these outlets are adjustable, so that flow rates, hence for micro-sprays the throw of the water, can be adjusted as required. Spray-nozzles are generally available in quarter, half and full circle spray patterns.

Other Fittings

There are a huge range of fittings that are readily available from hardware stores, irrigation suppliers, nurseries or garden centres, including: filters, pressure reduction valves, in line taps for isolating sections of your system, controllers (both manual & automatic), solenoid valves for automatic systems, tap connectors, and stakes (to support risers).

Some Design Considerations:
  • When installing micro-jets or sprays make sure you have plenty of overlap of the spray patterns. This helps ensure a move even coverage, and reduces the risk of damage to plants from lack of water if one of the nozzles gets blocked.
  • Pressure reduction valves may be required to reduce water pressure, otherwise you are likely to have leaks in your system or to have fittings blown off.
  • Backflow valves are also necessary to prevent water from the irrigation system re-entering your water tap, which could possibly affect water quality in your mains system (e.g. contaminants from the irrigation system such as pests/diseases, or sediments).
  • Filters should always be installed in each main line to reduce the likelihood of sediments building up and clogging the pipes or attachments.
  • When installing a system it can be either above or below ground (or both). Lay it down first on the surface while you follow your plan. Use connection pieces rather than forcing the hose round sharp bends.
  • Flush out the system well before connecting any nozzles.

How long and when to water
  • In sandy soils you can usually apply a lot of water quickly and it will be easily absorbed.
  • In heavy clay soils you should water slowly over a long period. Heavy applications will not soak in quickly enough, and a lot will be lost as run off.
  • Deep rooted plants such as trees should be watered slowly over a long period, so as to wet the soil to a greater depth.
  • Deep rooted plants can be watered less often than shallow rooted ones. Shallow rooted plants such as annual flowers and vegetables need frequent watering, but of a shorter duration at each watering.
  • Consider the time of day when you are watering. It is best to water when the plants will gain the most benefit and won't lose a lot of water through evaporation and transpiration. This is normally worse when it is windy, hot, dry, and sunny. So if these conditions apply in full or part, try to water early in the morning or/and evening.
  • Just because the garden looks wet doesn't mean that the water has reached the plant roots. Take a stick and dig under the soil in your garden to see how deep the water has penetrated. Infrequent deep watering is far more preferable to frequent light shallow watering as it encourages the roots to expand downwards and outwards seeking the deeper water.
  • In cold climates, particularly winter, water with micro-sprays in mid-morning, and not at all during the evening due to the risk of water freezing on the plants overnight which can cause damage to some plants.
Prevention of Clogging

The advantages of this type of irrigation are numerous, but these can be nullified by clogging of the delivery points. This in turn can lead to isolated dry spots in a crop, and in the extreme, death of the effected plants.

To help counteract this problem, the following measures should be considered.
  • Installation of a reliable filtration system for the irrigation system.
  • Regular inspection of all watering points to check for blockages.
  • Regular flushing or washing of filters.
  • Flushing of the whole system, ideally at least once a year, with clean water to remove any debris. Nozzles can be removed, washed clean in a bleach solution, and then replaced.
  • If your irrigation water is of poor quality then pre-treat it (e.g. run it through a large scale filter or through a settling pond to remove sediments) before using it for irrigation.

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