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How to install drip irrigation

Drip irrigation puts water exactly where the roots are and wastes very little. But a dripper's opening is tiny. One grain of sand can block it, and mains pressure can blow it off the pipe. Filter it, regulate it and flush it.

Why drip?

• Water goes into the soil at the roots, not onto leaves or paths.
• Little is lost to wind and evaporation.
• The surface between plants stays dry, so fewer weeds grow.
• Leaves stay dry, so vegetables get less fungal disease.
• It works on low pressure and flow, and under mulch.

Drip is not ideal for lawns. Sprays or rotors are better there.

Types of emitter

• Point drippers, punched into a pipe or on thin micro-tube: for pots, shrubs, trees and widely spaced plants. Choose 2, 4 or 8 litres an hour for each plant.
• Inline drip line, with drippers built in every 30 cm or so: for beds, rows of vegetables and hedges.
• Micro-sprayers: for ground covers and dense beds.
• Bubblers: for tree basins.

Pressure-compensating (PC) emitters give the same flow over a wide range of pressures. Use them on slopes, on long runs, and where watering must be even. Ordinary emitters are cheaper and fine for short, level runs.

Build the zone in this order

1. Backflow protection on the tap.
2. A valve or tap timer.
3. A filter fine enough for drip. Disc filters suit dirtier water from tanks and boreholes.
4. A pressure regulator set to the drip pressure, often about 1 to 1.5 bar.
5. A supply pipe, for example 16 to 20 mm poly pipe.
6. Drip line, or pipes with drippers.
7. Ends that you can open to flush out the dirt.

Many drip zones fail because they were connected straight to mains pressure with no filter.

Laying drip for different plants

Beds and vegetables

• Lay inline drip line along each row, or in parallel lines 30 to 45 cm apart. Space them closer in sand and further apart in clay.
• Pin the lines down and cover them with mulch, not soil, so that you can find and repair them.
• Lay the drip line before planting, so that seedlings go in beside the emitters.

Shrubs and trees

• Give each shrub one or two drippers at the edge of its root ball.
• Give a tree a ring of drippers under the edge of its canopy, not against the trunk, and widen the ring as the tree grows.
• Bigger plants need more drippers, not a longer run time for the whole zone.

Pots

• Fit one or more drippers to each pot: 2 litres an hour for small pots, 4 to 8 for large ones.
• Pots dry quickly. Short, frequent runs suit them better than one long run, when the water simply runs through.

Stay within the limits

• Zone flow: add up the emitters and keep the total within about three-quarters of your tap's flow.
• Run length: every drip line has a maximum length, which the maker states. Feed long beds from the middle or from both ends.
• Slopes: use PC emitters, and run the lines across the slope.

Converting old sprinklers to drip

Fit a filter and regulator after the zone's valve, cap the pop-up heads that you no longer need, and run drip line from the old head positions into the bed.

Tank, greywater and borehole water

• Tank water carries silt. Use a disc filter and flush often.
• Greywater carries soap, lint and hair. Ordinary drippers block within days, so use purpose-made greywater emitters.
• Borehole water may carry iron, sand or lime. Filter well and flush often.

Check the emitters weekly at first, until you know how fast they block.

This guide is based on Chapter 6 of Garden Irrigation DIY.