Winterizing Greenhouse Irrigation, Taps and Water Butts

Water expands, and it does not care what it is in

Water gains roughly nine percent in volume when it freezes, and it does so with enough force to split anything containing it. That is the whole problem, and it applies equally to a plastic drip line, a brass timer body, a pump housing and a buried supply pipe.

Two things make greenhouse water systems worse than garden ones. They are usually a patchwork of adapters, splitters and cheap components assembled over several seasons, and every joint is a candidate. And they are frequently the last thing anyone thinks about, because they sit there working invisibly all summer.

The job is small: an hour with a screwdriver, some fittings and a bucket. It sits at stage six of the fall changeover sequence, at or just after first frost, and it is the one job where being a week late can cost real money.

Drip lines and micro-irrigation

Drip components are thin-walled plastic, and they split readily. Emitters are worse than tubing, because the internal labyrinth is a narrow channel that holds water and cannot drain by gravity.

1. Turn off and disconnect at the supply.
2. Open the far end of every line and let it drain. Lifting the line and walking it toward the open end pushes standing water out of the low spots.
3. Blow the lines through if you can. Low pressure from a compressor or even a pump-up sprayer clears emitters that gravity will not. Keep the pressure well below the line's rating — you are clearing water, not pressure testing.
4. Cap or leave open? Leave open. A capped line traps whatever moisture remains; an open one keeps draining and dries out.
5. Coil and store anything removable. Tubing left in place through winter is fine; tubing left full of water is not.

Timers, filters and pressure reducers

These are the expensive parts and they all fail the same way. A battery timer holds water in its valve body, that water freezes, and the diaphragm or housing cracks. You will not find out until spring, when it either leaks continuously or does not open at all.

All of it comes off and comes inside: timers, inline filters, pressure regulators, fertiliser injectors, solenoid valves and any pump. Drain each one, shake the water out, dry it, and store somewhere frost-free. Take the batteries out of timers while you are there — a battery left in over winter leaks and corrodes the contacts.

Put them all in one labelled box. The single most annoying part of spring setup is finding five of the six components you need.

Outside taps and supply pipes

This is the failure with real consequences, because a split supply pipe can be inside a wall or under a path.

If there is an internal isolating valve for the outside tap, close it, then open the outside tap and leave it open so the section between valve and tap can drain and any residual water has room to expand. Leaving it closed with the isolator shut is the mistake — you have sealed water into a pipe with nowhere to go.

If there is no isolator, insulate. A purpose-made tap cover, or lagging plus a bag, over a tap that has been drained as far as it will drain. Insulation slows freezing rather than preventing it, so this is a mitigation, not a fix.

Disconnect hoses. A hose left attached holds water against the tap and defeats any draining you have done.

Water butts and tanks

A full water butt is unlikely to freeze solid in most climates, because the volume is large and the thermal mass considerable. What does happen: the surface freezes, the tap freezes, and repeated freeze-thaw at the seams and the tap boss works them loose until they leak.

The autumn routine:

• Drain and clean at least once. A season of leaf litter and algae is a disease reservoir feeding your watering can, and autumn is when the leaves arrive.
• Scrub the inside with a stiff brush and rinse. Leaf-stained water breeds and it goes on your plants.
• Clear the gutter and any filter before the leaves fall properly, then again after.
• Leave it part full rather than brimming. Headroom gives ice somewhere to go.
• Fit or check the lid. Keeps leaves out, keeps light out, keeps children and wildlife out.
• Insulate or remove the tap if it protrudes and freezes — taps and their fittings are where butts usually fail.

How you water for the rest of the season

Winterizing the system is also the moment to change the habit, because the system that ran all summer is the wrong system for winter anyway.

Water in the morning, so surfaces dry before the cold still hours. Water at the roots, never over the foliage. Water far less — a plant that is not growing barely transpires, and winter overwatering causes both root rot and the surface humidity that gray mold needs. A watering can with the rose removed is the correct winter irrigation system for most hobby greenhouses. See autumn condensation and gray mold.

Keep a can of water standing in the greenhouse so it is at house temperature when you use it. Cold mains water on roots at eight degrees is a check to plants that are already struggling.

What you need

The one-hour checklist

1. Isolate the supply at the internal valve, or at the tap.
2. Open every line at its far end and walk the water out.
3. Blow lines through if you have the means.
4. Remove timers, filters, regulators and pumps. Drain, dry, debattery, box, label.
5. Leave the outside tap open if isolated internally; cover it if not.
6. Disconnect and drain hoses; store them coiled and out of sunlight.
7. Drain, scrub and part-refill the water butt. Check lid and gutter filter.
8. Put a watering can inside the greenhouse and switch to hand watering.

Eight steps, one afternoon, and the difference between opening the box in March and finding a working system or six cracked components and a spring irrigation rebuild.

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Common questions