Greenhouse watering-timer guide

Identify the system the timer will control

The common mistake is buying a timer before choosing the water source. A tap timer is a valve: it opens and closes a supply. It cannot pressurise a water butt or distribute water evenly through poorly designed tubing. Write down whether you have a mains tap, a raised gravity reservoir or a pump drawing from stored rainwater. Check the published pressure and fitting requirements of the entire chain—controller, filter, regulator, hose and emitters.

The Hozelock Select controller below offers 16 preset programmes, but those choices do not tell you how long your tomato bags need to be watered. It is a controller alone. The Hozelock 20-pot kit includes a Select controller and drippers for a compatible tap-fed supply. A water-butt pump system such as the Irrigatia SOL-C36Q is a different architecture, with its own solar-powered control. See the water-butt irrigation guide before treating them as equivalents.

Set a schedule from measured water, not a guess

Map each pot and estimate a starting irrigation zone. Place an emitter near each root ball, secure tubing and run a manual test. Catch the output from several emitters in measuring jugs for a known duration. If the farthest outlet is much weaker, address pressure, kinks or layout first; programming a longer cycle can overwater the nearest pots.

Check the compost beneath the surface after a cycle and again before the next one. A small seed tray, a hanging basket and a mature growbag rarely need the same dose. Divide them into separate circuits or keep the odd containers on a hand-watering routine. The greenhouse drip-irrigation guide covers emitters and zones in more detail. Avoid a timer schedule that leaves standing water or constantly wet foliage in a closed greenhouse.

Plan for failure, not just convenience

Fit fresh batteries at an appropriate interval, clean the filter, check joints for leaks and inspect each outlet. Test the system through several normal days and one warmer day before relying on it. If the controller has a manual function, use it to confirm valve and flow rather than assuming a programmed display proves water reached the plants.

Water storage and supply reliability matter too. A pump cannot draw from an empty butt; a tap may be unavailable under restrictions; a smart controller may lose connection. The RHS watering-methods guidance also highlights appropriate backflow separation for permanent mains irrigation. Check current water-company rules and use a qualified plumber for an uncertain connection. For holidays, give a trusted person a clear check-and-refill plan using the watering-while-away guide.

When a working timer still leaves dry pots

Separate a control fault from a distribution fault. First use the manual cycle and check that the valve or pump runs. Then inspect the supply level, filter, tubing and representative outlets. If every emitter is weak, the supply or pressure may be unsuitable; if only one is weak, check that branch for blockage, a kink or a displaced dripper.

If measured output is adequate but compost stays dry in part of a container, reconsider emitter position and how the water wets the root zone. Do not simply double every programme: that can flood the containers that were already receiving enough. Record the change, retest the outlets and observe the next few cycles before leaving the system unattended.

Review through the season

As crops grow, containers fill with roots and weather changes, the same timed dose may become insufficient or excessive. Inspect leaves and root-zone moisture rather than only the clock. Keep a short record of schedule changes and which zone they affect. Automation should make a measured watering plan repeatable, not replace plant observation.