How Long Should Drip Irrigation Run for Hedges?

Set the Timer by Water Delivered, Not Time Alone

There is no single runtime that suits every hedge irrigation system. Two pipes can run for the same length of time while delivering very different quantities of water.

A pressure-regulated drip line may contain individual outlets with a stated litres-per-hour output. A porous pipe releases water gradually through the wall of the hose, with its performance affected by pressure, pipe length and installation. Hedging Plants Direct’s irrigation pipe contains internal nozzles designed to control water flow along the hedge, while Bronte Porous Pipe is designed to operate at low pressure.

Where the manufacturer provides an output in litres per metre per hour, use this calculation:

Required litres per metre ÷ output per metre per hour = runtime in hours

For example, if a drip line delivers 4 litres per metre each hour and you want to apply 8 litres per metre, the calculated runtime is two hours.

This calculation provides a starting point. The soil must still be checked because water may spread differently through clay, loam and sandy ground.

How to Test the Correct Runtime

The most reliable way to set a timer is to test the system in the actual planting area.

1. Begin With a 30-Minute Test

Run the irrigation for 30 minutes. This is long enough to begin showing how quickly water is being delivered and how it moves through the soil, without committing to a long watering cycle immediately.

2. Check Beneath the Surface

Move aside any mulch and inspect the soil approximately 10 to 15cm below the surface. With a newly planted hedge, check both the original root ball and the soil immediately around it.

The aim is to moisten the complete root area. A damp surface with a dry root ball underneath means the system has not run for long enough. Surface appearance alone can be misleading because soil may remain dry around the roots even when the top looks wet.

3. Inspect the Complete Hedge Line

Check at least three positions:

• Near the water supply
• In the middle of the hedge
• At the far end of the irrigation run

Do not assume that water reaching the first few plants means the complete hedge is being watered. A kink, blocked outlet, pressure loss or damaged section can leave part of a long hedge dry. HPD’s care guidance also recommends checking the beginning, middle and end of an irrigation run.

4. Increase the Runtime Gradually

If the root zone is still dry, increase the next test by 15 to 30 minutes.

Continue until water has reached the depth and width of the active root area. If water begins pooling on the surface, running downhill or leaving the soil saturated for a long period, shorten the cycle or divide it into two separate watering periods.

How Soil Type Changes the Irrigation Time

Sandy and Free-Draining Soil

Sandy soil allows water to move downwards quickly and may dry again soon afterwards. The irrigation may need to run more frequently, although each session should still be checked to ensure water is not simply passing below the active roots.

Mulch can help reduce evaporation and slow moisture loss from lighter soils.

Clay and Heavy Soil

Clay holds water for longer and absorbs it more slowly. A very long uninterrupted cycle may produce puddles or surface run-off before moisture has spread evenly through the root zone.

It may be better to split the watering into two shorter cycles, allowing time between them for the water to soak into the soil. Do not irrigate clay ground that is already saturated.

HPD’s guidance explains that free-draining soils usually require closer watering, while heavy soils retain moisture for longer and can become waterlogged if too much water is applied.

How the Size of the Hedge Affects Runtime

Small bare-root whips have a much smaller initial water demand than large pot-grown, root-balled or instant hedge plants.

A substantial evergreen hedge carries a large amount of foliage but initially relies on a restricted root system. It can therefore lose water more quickly than its newly planted roots can replace it, particularly during warm or windy conditions.

For larger plants, a 30-minute cycle may only wet part of the root ball. These hedges may need a longer cycle, two irrigation lines or closer monitoring during their first growing seasons. Semi-mature and instant hedging requires especially careful watering during establishment.

Where Should the Drip Pipe Be Positioned?

For a newly planted single-row hedge, position the irrigation pipe over the root area rather than against the stems or along the outside edge of the planting strip.

Where plants have wide root balls or have been planted in a staggered double row, two irrigation lines may provide more even coverage than one narrow central line.

The pipe can normally sit beneath the mulch but above the soil where it remains accessible for inspection and repair. Test the complete system before covering it. HPD’s Laurel care guide recommends positioning irrigation close to the centre of the root balls and considering two lines for wide root systems or double-row planting.

You can view the complete Hedge and Garden Irrigation system for pipe, connectors and pressure regulation.

How Often Should Hedge Irrigation Be Run?

Runtime and frequency must be considered together. A slow, thorough application is generally more useful than repeatedly wetting only the top few centimetres of soil.

Newly planted hedges require regular monitoring during dry weather while roots spread into the surrounding ground. The RHS recommends keeping new hedges well watered through their first two years. Established hedges normally require much less additional water, although prolonged hot, dry or windy periods can still create drought stress.

Do not continue running the irrigation simply because the timer is programmed. Reduce or pause it after substantial rainfall and whenever the soil remains moist at root depth.

Signs the Irrigation Has Not Run for Long Enough

Possible signs include:

• The soil surface is damp but the original root ball remains dry
• Leaves droop, curl or become crisp at the edges
• New shoots wilt or stop extending
• Plants at the far end of the line decline first
• One isolated plant remains dry because an outlet is blocked

Inspect the system before simply extending the timer. Increasing the runtime will not correct a blocked nozzle or poorly positioned pipe.

Signs the Irrigation Is Running for Too Long

Possible signs of excessive watering include:

• Water standing around the hedge after irrigation
• Soil remaining saturated or smelling stagnant
• Yellowing foliage while the root area is wet
• Decline concentrated in low points along the trench
• Dark, soft or poorly developed roots

These symptoms can also be associated with compacted soil or inadequate drainage. Stop irrigating and inspect the ground before applying more water.

Adjust the Timer Through the Seasons

A setting that works during a hot, windy week may apply too much water during cooler weather.

Check the soil regularly and adjust the programme after rainfall, temperature changes and periods of strong wind. Newly planted hedges need the closest attention, while established hedges can normally be watered less frequently and mainly during extended dry spells.

Recording the runtime that works for your soil and irrigation system provides a useful starting point, but the condition of the root zone should always take priority over the timer.