How to choose your underground irrigation?

The water needs of your garden or plant nursery can be satisfied either by sprinkling or direct irrigation through the soil.

An underground 'irrigation' circuit can in fact achieve either type of watering, through the use of microporous tubes or drip-by-drip feeders (irrigation) or sprinklers, turbines or sprinkling nozzles (sprinkling).

In either case, an underground watering system consists of an assembly of pipes connected in a closed circuit. It can be supplied with water from the mains, or a rainwater collector or well (in these two cases you'll need to install a surface or submersible pump). This kind of watering system will ensure the survival and healthy growth of your plants by catering regularly to their water needs.

An underground watering system can be automatic and controlled by a specialized timer. Depending on tech level, it might allow daily or weekly programming and may even come equipped with a hygrometric sensor. This enables the system to override its regular watering programme on rainy days and while the soil is saturated after heavy precipitation.

The appropriate size of pipes and watering nozzles (etc.) will depend on the pressure and flow rate supplied by the mains network or other supply source.

An underground watering system requires pipes to be installed in order to channel the water to the turbines, nozzles or drip-by-drip heads. These pipes must be chosen carefully: they should be high quality and positioned so as to avoid excessive pressure losses. To achieve this, the pipes should be of the correct diameter and length, and bends kept to a minimum (i.e. changes of direction).

There are two types of underground watering system:

• drip-by-drip

• turbine or nozzle

Any type of watering system requires an appropriately sized polyethylene supply pipe - which can either be low- or high-density.

Low-density polyethylene pipe

Often fairly small in diameter, between 16 and 20mm, these are perfect for drip-by-drip systems that don't need to travel more than 25 metres in a linear direction (lm) and with pressure not exceeding 4 bars (B). Note that this still allows for several branches each travelling 25lm.

High-density polyethylene pipe

Covering diameters from 25 to 50mm, these pipes are perfect for heavy-duty turbine or nozzle systems (up to 100lm per branch) and with pressures of up to 6B.

For a successful installation, you need to find a balance between the required pressure, minimum flow rate for effective watering, and the length of the various branches of your circuit. Just so you know, the majority of watering circuits use pipe diameters between 25 and 32mm.

Calculating flow rate

It's essential that you know the flow rate of your supply source before you go to choose your watering equipment. To do this, take a 10l bucket and record how many seconds it takes for it to fill from the tap (ideally the one you plan to use to supply your watering circuit) when fully on. Divide 36 by this number of seconds to obtain the flow rate in m³/h:

Flow rate in m³/h = 36 / filling time (seconds)

Worked example: a 10l bucket filled in 12 seconds demonstrates a flow rate of 3m³/h

36/12 = 3m³/h

Supply pipe characteristics for underground watering systems

To construct your underground watering system, you'll need to assemble a range of components. Starting from the point where your pipe network takes in water from the supply source, via the installation of solenoid valves, to the turbines, filters, etc., you'll need to make sure you have all the right connections.

These connections can be elbow joints or junctions (sleeves, T-joints) between two equivalent components or adaptators between different types of component.

Connections should be chosen depending on pipe diameter, fitting type (screw or push-fit) and network pressure. To a lesser extent, material is also important - although with the exception of the supply network (which might be metal, e.g. copper), your network is very likely to be made up of polyethylene pipes.

Circuit accessories

Type of watering network connections

Turbines are an essential element of underground watering systems. This is what spreads water over an area of your garden or lawn under the action of pressure.

It's important to distinguish a turbine from a nozzle - although they do work in a similar way and are both collapsible. Turbines and nozzles are both installed in the ground and connected to the circuit so that when it's filled with water, the pressure lifts the collapsible part to enable watering to start.

  Turbine

A turbine is a longer-range sprinkler, effective at 5 to 12 metres, which spreads water in a circular or customizable pattern (i.e. partial circular arc) for watering a particular area of vegetation. It can also be set to an oscillating pattern.

Turbine watering characteristics

Installation advice

A watering system, on the surface or underground, is an assembly of components connected by pipes which are themselves connected by a range of fittings - elbows, T-joints etc. These components require specific levels of pressure and flow to operate correctly; these should be considered carefully for optimal installation.

If your supply pressure is limited to 3B, it's a good idea to install a booster pump upstream of your watering circuit if you need more capacity. Submersible, surface and motor pumps should be sized to suit your circuit needs (output pressure and flow).

In order to minimize pressure losses, reduce the number of connections, and especially changes of direction and excessive lengths of pipe; and remember that a parallel is always better than a serial configuration. Otherwise, you risk ending up with a feeble pressure level at the end of your circuit.

Depending on your needs, turbines or nozzles may not be the best watering solution for you. It's always possible to install watering points for manual or automatic sprinklers.

These are also supplied by an underground line, similar to turbines, with screw fittings (3/4 or 1’’ or 20 x 27 / 26 x 34mm.

With the help of a quick connector, a hosepipe and spray gun or sprinkler can be used easily and conveniently.

Note that watering points can be protected by anti-frost outlet valves for use in colder regions.

To find out more about gardening, follow our editors' advice and check out their other guides:

When to water your garden?How to choose your rainwater collector?How to choose your surface pump?How to choose your submersible pump?How to landscape and decorate your garden?How to maintain your lawn?How to choose your booster pump?How to choose your motor pump?How to water your lawn?How to choose your watering timer?How to choose your planters?When to plant a tree?How to choose your drip-by-drip irrigation system?How to arrange and decorate your garden?When to sown your lawn?How to choose your watering attachments?How to choose your tools to work soil?When to trim your hedges?How to decorate your balcony?How to choose your hosepipe and reel?How to choose your hose nozzle or gun?How to choose your watering can or sprinkler?How to trim your hedge?How to choose your lawn?How maintain your lawn?