Greenhouse drip-irrigation guide

Design the crop zones first

Drip irrigation becomes difficult when every plant is connected to one line regardless of demand. Divide the greenhouse into groups: propagation trays, small pots, mature fruiting containers, growbags and soil beds. Each group should tolerate the same watering frequency and broadly similar application.

Draw the layout at mature plant size. A clear tube route in April can become inaccessible behind tomatoes in July. Include the water source, controller, filter, regulator, isolation valves and line-end flush points.

Choose the water source

Mains tap

A mains tap offers stable pressure and suits many packaged kits. Fit the backflow protection, pressure control and connectors required for the intended irrigation use. Water Regs UK notes that risk depends on system design, setting and chemical additives, and the local water undertaker decides whether category 5 protection is required.

Never submerge an open hose in a fertiliser tank or reservoir connected to drinking water. A tap timer or trigger valve is not automatically a backflow-prevention device.

Rainwater butt

Collected rainwater is useful for greenhouse plants, but debris, algae and low pressure have to be managed. Use a covered butt, accessible filter and a drip system explicitly rated for the available gravity head. Raising a full butt introduces substantial weight, so use a stable purpose-made stand on a sound base.

If a pump is required, choose one compatible with the water, desired flow and duty cycle. Electrical installation near water needs professional planning, RCD protection and equipment suitable for the environment.

Independent reservoir

A covered reservoir with a small pump can supply a greenhouse without a nearby tap. Calculate daily demand from measured output rather than the pump’s maximum headline flow. Include a low-water cut-out or other protection if the pump must not run dry.

Filter before the small passages

Drippers rely on narrow flow paths. Fit the filter specified by the system before the distribution tube, where it can be isolated and cleaned without emptying every line. A clear housing is helpful only if it is protected from light that encourages algae.

Flush the mainline before attaching emitters, then flush each branch. Repeat after repairs, at the start of the season and whenever end-of-line output falls.

Regulate pressure

Tap pressure can exceed what small push-fit connectors and emitters tolerate. A compatible regulator protects fittings and helps outlets deliver more evenly. Place it in the sequence specified by the kit—often after the tap controller and filter—and respect flow direction.

Low pressure creates a different problem: the first emitters work while the last barely drip. Shorten the run, reduce the number of outlets, create separate zones or use pressure-compensating emitters within their stated range. Do not solve it by opening adjustable heads until the first pots flood.

Route the mainline safely

Run the larger supply tube along the staging or greenhouse perimeter and branch to plants with short micro tubes. Secure it with clips that do not crush the bore. Avoid tight bends, hot metal edges, door runners and the central path.

Where a line crosses a threshold, reroute it overhead only if properly supported and away from heads, vents and heaters; otherwise protect it in a suitable conduit. A trip hazard is a poor trade for a short route.

Select emitters for the growing medium

Adjustable drippers suit mixed pots but require balancing. Fixed-flow drippers are easier to compare. In-line drip pipe suits uniform rows, while individual stakes make container positions obvious.

Watch the wetted area during a full cycle. Peat-free and bark-rich composts can shrink from pot sides or wet unevenly. Move the emitter, split the flow between two points or slow the application so water infiltrates rather than escaping down one channel.

Seed trays often need a separate fine-control method. A dripper in one cell does not irrigate a whole module evenly, and overhead misting can raise disease pressure. Capillary matting or hand watering may remain better for propagation.

Add a timer only after the hydraulics work

First prove that water reaches every outlet at acceptable flow. Then add a timer compatible with the source pressure and desired frequency. Programme a conservative cycle and observe at least a week of normal weather.

Greenhouse demand changes quickly. Lengthen or add cycles as plant canopy and fruit load grow; reduce them during dull weather. Separate zones are better than forcing one duration to suit every crop.

Run a catch-cup test

Place identical measuring cups under at least one emitter near the start, one in the middle and one at the end. Run the system for ten or fifteen minutes and compare collected volumes. Repeat for every emitter if the system is small.

Calculate output per hour from the measured interval, then translate the schedule into approximate volume per plant. Record the result near the controller. Repeat after changing the layout, cleaning the filter or adding emitters.

Inspect soil moisture, not just surface colour

Push a finger or suitable probe into the root zone and check container weight. The surface can look wet while the lower root ball remains dry, or dry while a saucer stays saturated. Lift a representative pot after a cycle and examine drainage.

Place emitters securely so they cannot spray the stem, aisle or electrical equipment. In growbags, spread outlets across the bag rather than creating one permanently wet pocket.

Maintenance routine

Weekly, inspect each outlet while running, clean the filter and look for green algae, white mineral deposits, rodent damage and connections under tension. Monthly, compare catch-cup volumes and flush line ends.

At the end of the season, drain exposed tubing and store the tap controller or pump as directed. Label zones before dismantling. Replace hardened micro tube rather than pushing it back onto a fitting that can no longer seal.

Holiday preparation

Run the final programme for several days before leaving. Confirm reservoir capacity, fit an overflow route that cannot flood the greenhouse, secure emitters and change batteries early. Ask a trusted person to check plants and the water source; a remote alert cannot reconnect a tube.

Sources and related guidance

Water Regs UK guidance on hose union taps explains irrigation backflow risk and the role of the local water undertaker. Compare complete kits in best greenhouse watering systems and plan hot-weather demand alongside greenhouse ventilation.