Drip Irrigation

Drip irrigation is the most elaborate and expensive system for watering a small area. Using a complex array of plastic distribution pipes connected by cross or T-connectors, water is fed continuously to individual plants in the garden or greenhouse via special drip-feed nozzles.

Each pipe must be cut to length so that a constant water pressure can be maintained throughout the system. Nozzles are held slightly above the soil using forked or clip-type pegs. The nozzles can be adjusted to balance the drip flow, but need regular cleaning to remove lime scale and soil blockages caused by splashing or cultivation. You can even fit a watering computer to regulate the system automatically.

Irrigation Systems

The disadvantage of all these systems is that they depend to a greater or lesser extent on someone to set them out, move them around and turn them on and off. The ideal garden watering system is a permanent (or at least semi-permanent) installation which just needs turning on as required, or which can be left on permanently in really dry weather or when you go on holiday to provide a continuous supply of water.

You can install two basic types of irrigation system. The first uses a system of underground pipework which feeds fixed spray heads and other watering devices positioned at chosen intervals round the system. The second uses flexible hose pipes laid on the soil surface from which other pipes are branched off using T-couplers to feed individual areas. You simply attach miniature spray heads or drip feeders wherever you want them along the branch pipes, turn on the water supply and leave the system to do its work around the garden unattended.

Fixed Systems

A fixed underground system is the better choice if your garden is ‘static’ – if, in other words, the basic layout and the positions of flower-beds and individual plants are unlikely to change in the near future. Several manufacturers supply spray heads, drip feeders and other components; you supply and fit the system pipework, which is usually run in rigid PVC with fixed elbows and Ts, just like solvent-welded wastepipe runs inside the house.

First of all, plan where the main pipe runs will be needed. The best way of doing this is draw out a scale plan of the garden on squared paper. Indicate where the main spray heads will be required – down each side of the lawn, for example, so their spray patterns overlap – and plan branch runs as necessary to supply drip feeders to individual areas or plants. You can then work out how many spray heads, drip feeders and other components you require, and also how much pipe and how many fittings you need to buy.

Your local water authority may require you to fit an anti-siphon or non-return valve at the point where you take your supply off the main, and they will certainly require the system to have its own stoptap. They may also increase your water rates.

The actual installation involves digging trenches about 20cm deep. Start work at the point where the system is connected to the water supply and work outwards, laying the pipe in place on a bed of sand or sieved soil and welding pipe joints, elbows and Ts for branch pipes to the main pipe as required. Add Ts pointing upwards where necessary to supply either individual spray heads or drip feeders.

When all the welds have set hard – allow up to six hours for this – turn on the water supply and flush it through to clear out any debris in the pipes and to provide a visual check for any leaks. When you are happy that everything works, back-fill all the trenches. Make sure all the takeoff points are above ground level.

Flexible Systems

Flexible irrigation systems are a better choice if your garden is in a continual state of flux, since you can easily adapt the layout accordingly. Instead of being buried deep underground, the supply pipe – in reality just special hose pipe – is laid on or just below the soil surface, with Ts supplying branches as your layout demands. Then all you have to do is attach the spray heads and drip feeders directly to the supply hose, either using special snap-on connectors or by screwing them into holes pierced in the wall of the hose.

Various types of spray head are available, offering spray patterns of different sizes and shapes. The drip feeders can be connected to lengths of small-diameter plastic tubing to take water to individual plants some distance away from the main supply hose, and these are almost invisible if covered with a little soil.

The main difference between fixed and flexible systems is the water pressure; flexible systems operate on fairly low-pressure water – you can fit a pressure regulator in the supply pipework just after it leaves the main supply point, and adjust it to give the flow rates you require at the various outlets. The other difference is that the outlets can easily become blocked by particles of grit, soil and so on, so a water filter is usually fitted just after the pressure regulator. You should clean this out at regular intervals to reduce the risk of a blockage.