21st Century Irrigation:

Lush, verdant borders and thriving planters even in the height of Summer can be achieved effortlessly using highly water efficient irrigation systems. Incorporating an irrigation system into a landscape project not only helps the planting look great in dry weather, it also speeds up establishment and reduces plant losses. In this article we look at the best ways to water lawns, borders and planters, as well as more innovative applications such as green roofs; we shall also look at some of the fundamentals of irrigation, and also consider questions such as how often to water.

The best way to water:


Many homeowners think that it is the lawn that benefits most from irrigation, but in actual fact it is the border where irrigation can make the most difference. A large border will be planted with many hundreds if not thousands of pounds worth of plants. Regular irrigation will make a big difference, not only reducing losses, but allowing the border to reach maturity much more quickly.

There are two main ways of irrigating borders: drip lines or micro sprinklers. Drip lines are much more water efficient and can be placed under a mulch to make them invisible. Some driplines are designed to allow them to be buried a few inches under the soil, although this does cause more maintenance issues and the system cannot be connected directly to the mains water supply.

The alternative solution is to water using sprinklers placed in the border. These are easier to install into established beds, and when operating provide visual interest, however they are not as water efficient and can have problems with dry spots in the border, especially when the border becomes more established.

For the maximum water efficiency, lawns can be watered with drip lines laid beneath the turf, but this is very time consuming to install and does present problems if the lawn needs aerating.

The most common way of watering a lawn in using pop-up sprinklers located in the lawn itself. As the system operates the sprinklers rise out of the ground to water. There are two types of sprinkler; rotor sprinklers for large areas, where a single jet of water rotates slowly back and forth over a pre-set arc; and spray sprinklers which are designed for small areas. Spray sprinklers generally are very thirsty, but a new generation of spray sprinklers have come on the market which are much more water efficient.

Baskets and Tubs
Providing irrigation to tubs and baskets is fiddly, but well worth the effort as the small compost area allows the plants to dry out quickly. With a dripper in every pot and very slim pipework to connect everything together, a patio planting scheme can be discreetly watered several times a day – keeping everything looking vibrant.

Trees and Hedges
Trees and hedges need a lot of water and are very costly to replace, so it makes sense to install irrigation at the same time as planting. For hedges generally one or two lines of drip line are run along the base of the hedge with drippers set at a close spacing – typically 0.3m apart. With modern pressure compensated drip lines it is possible to achieve uniform drip rates over 200m long runs.

For small trees a necklace of drip line can be placed around the tree, again using a closely spaced drip line. For larger trees a new system called StrataRoot is designed to put larger volumes of water deep down into the root zone. The device is 36” deep and ensures that air as well as water gets down to the root zone.

Green Roofs
There has been an explosion in green roof projects as their environmental credentials have been established. Roof gardens and grass roofs will need irrigating on a regular basis, whilst sedum type green roofs will only require irrigation during their establishment or if they are on a pitched roof. Temporary sprinklers may be used for establishment, sub-surface drip lines are used on extensive green roof structures for longer term watering.

Sports Turf
The most common way of irrigation sports turf is using pop-up sprinklers buried in the turf, although for smaller establishments solid set sprinklers can be placed on the pitch and connected up using hosepipe when watering is needed. A set of 6 sprinklers will cover a strip of grass the width of a football pitch and can be run from a good mains water supply. The sprinklers can be progressively moved down the length of the pitch to water it all.

Water Regulations
It is very easy to break the law with an irrigation system, so it is important to know the regulations if you are selling irrigation to your clients. The Water Supply (Water Fittings) Regulations 1999 regulates water use in England and Wales. The primary aim of the act is to ensure that drinking water is kept clean and wholesome.

For irrigation, what the act calls ‘house gardens’ have less regulations than commercial premises. For a private house, all outside taps must have a double check valve fitted. With this we can then use irrigation systems where the emitter is more than 150mm above the ground, so we can use systems such as sprinklers in the borders.

If we add a ‘DB’ valve to the tap, we can then run irrigation that is on the surface of the soil, such as drip lines in borders and drippers in baskets and pots. A ‘DB’ valve is easily screwed onto the outlet of the tap to provide compliance, although if you have a multi-zone controller you will need one per zone.

Pop-up sprinklers and buried drip line need either an RPZ valve or a break tank and pump to comply, which are much more expensive and really require professional design input.

Controlling the system
Dawn is the best time to water as the air is stillest and the humidity levels higher. Adding a simple battery operated timer to an irrigation system saves having to get out of bed, and a timer also has the advantage that it won’t forget to turn the irrigation off, and it will operate while the client is away.

As well as simple ‘tap timers’ more sophisticated battery controllers are available that will operate up to 4 separate zones.

For larger irrigation systems, mains powered controllers will operate multiple valves and provide much more sophistication. For really weather responsive irrigation, a mini weather station can even be added – producing water savings of up to 30%. Unlike conventional timed systems, with a weather station the watering times are automatically increased and decreased in response to the prevailing weather.

For timed systems the question is often asked “how often should I water’”. As a general rule planting with little water reserves such as patio pots should be watered several times a day. For established borders watering is best done several times a week rather than every day to provide a more natural wetting then drying cycle for the plants. Trees require a lot of water but again giving this in less frequent but more prolonged watering encourages the trees to develop deeper root systems.


‘Neglect the fundamentals at your peril’ is a good moto for anyone considering installing irrigation. Get these right and the irrigation system will work first time every time – get them wrong and disaster looms! With irrigation there are three basic points to consider – available water supply, water pressure and pipe size.

Every tap has a finite amount of water that will come out – add too many sprinklers or drippers and the system just won’t work. Pressure throws water from the sprinkler nozzle to water the lawn or border. Not enough pressure and sprinklers will dribble not spray and drip nozzles won’t operate. Putting too much water through a small pipe will result in the loss of pressure, so just as we need a wider road on the M25 than on a country lane, we need wider diameter pipes for high flows and smaller pipes for low flows.

Matthew Pearce
Access Irrigation Ltd
t. 01788 823811

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