Cold snaps and winter storm warnings have been in the UK forecasts this November. For a heated glasshouse, a freeze is not just uncomfortable. A failed boiler, a blocked vent or a power cut can damage a crop in hours, and the damage may not show until the following week. This is a seasonal checklist for growers who want to be ready before the cold arrives. It is general guidance, not a substitute for your own heating engineer’s advice.
Check the official forecasts regularly through the Met Office, and use the warnings as a prompt to act, not as a reason to panic.
Check the heating before the frost
Start with the heating system, because it is the part of the operation that cannot be left to chance. Ask your heating engineer to service the boiler or heat generators before the cold sets in, and to confirm that the controls, sensors and safety cut-outs are working. Ask them to walk through what happens if a boiler fails overnight.
Check the fuel supply as well. Confirm how much fuel you have in store, how long your supplier needs to deliver, and what they can do if a cold week drives up demand. For growers on bulk oil or LPG, a delivery that is planned in November is much easier than an emergency order in January.
If you have backup heating, such as a standby boiler or a portable heater, test it now. Make sure it is connected to the right supply, that you have the fuel for it, and that someone knows how to start it.
Set the points with a margin
Your set-point is the temperature the control system aims to hold. In a cold snap, the set-point alone is not enough. Look at the minimum temperature you can tolerate for each crop, and set your alarm threshold above it, so that you hear about a problem before the crop is damaged.
Consider a separate set-point for nights and days, and check how the system responds when the outside temperature drops quickly. Some glasshouses take longer to recover after a power interruption than the control panel suggests, so a short test run can show how the system behaves in practice.
Keep a written record of the set-points and alarm thresholds. A new member of staff who comes in at six in the morning should be able to see at a glance what the system is meant to do.
Alarms, monitoring and who gets the call
A frost or temperature alarm is only useful if someone responds. Check that the alarm dials out to a named person, that the number is up to date, and that the alarm can reach a second person if the first does not answer. Test it, and write down the result.
Consider remote monitoring if you do not have it already. Many systems can send alerts to a phone, so you do not need to be on site to spot a rising or falling temperature. Make sure the monitoring equipment has its own power backup, because a power cut that stops the heating often stops the monitoring too.
Agree a simple rota for the cold weather. Decide who checks the glasshouse overnight, who covers weekends and what happens if someone is ill. Writing the rota down in November means you are not making those decisions at midnight in January.
Power and standby equipment
Fans, circulation pumps, control panels and alarms all need electricity. If the power fails, the heating may stop even if the boiler is fine. Check whether your system has a generator or battery backup, and how long it can run the essential loads.
If you use a generator, test it under load before the cold arrives. Check the fuel, the connection and the ventilation, and make sure it is used safely. Never run a generator in an enclosed space.
Ventilation, screens and insulation
In a cold snap, growers often focus on heating and forget the effect of ventilation. Vents that are left open at night can cost you a great deal of heat. Vents that stick, or that do not close fully, can cause the same problem. Check the vent mechanisms now and fix any faults before the frost arrives.
Thermal screens can save energy when they are used well. Check that the screens close properly, that the edges seal, and that the control system uses them at the right times. Damaged screens can let heat escape without any warning.
Look for draughts around doors and at the ends of the glasshouse. Small gaps can make a noticeable difference to the heat load, and sealing them is usually a cheap job.
Protect the crop and the people
Cold air can damage plants in ways that are not obvious at first. Watch for leaf damage, slowed growth or wilting after a freeze, and check the root zone as well as the foliage. Hold back on heavy watering in very cold weather, because wet compost can chill quickly, and water in the morning rather than late in the day so the plants are not left wet overnight.
Keep staff safe too. Icy paths, slippery steps and hot pipes all carry risks in winter. Make sure the path to the glasshouse is clear, that there is a torch on site, and that anyone working alone knows the emergency contact.
A practical checklist before the freeze
- Service the boiler and test the controls, sensors and safety cut-outs.
- Confirm the fuel supply and the delivery lead time with your supplier.
- Test backup heating and check the fuel it needs.
- Set the temperature points with a margin above the crop’s minimum.
- Check the alarm dial-out and the named contact, then test it.
- Check vents, screens and door seals.
- Agree the overnight rota and write it down.
- Clear paths, check torches and confirm emergency contacts.
Key points
- Service the heating and confirm the fuel supply before the cold weather arrives.
- Set alarms above the minimum temperature each crop can tolerate.
- Test the alarm dial-out and make sure someone can respond at any hour.
- Plan for a power cut, including the monitoring equipment and any generator.
- Check vents and screens, because heat loss at night can be as costly as a failed boiler.
- Write down the rota and the emergency contacts so the plan works under pressure.
If you need help reviewing your heating set-up or your cold-weather plan, speak to your heating engineer first, and use our earlier article on greenhouse climate control basics as a starting point for the discussion.