How Can We Maintain the Humidity Inside a Greenhouse?
Manage greenhouse humidity by checking the air beside your plants, then adjusting ventilation and watering to suit the crop. Persistent condensation, wet leaves and stale air call for better air exchange and less unnecessary moisture. In hot, dry weather, suitable plants may benefit from damping down the floor. Use a hygrometer alongside a thermometer; one humidity target does not suit every crop or season.
Key Takeaways
- A hygrometer measures humidity; a thermometer measures temperature.
- Check conditions near the plants rather than against hot glass.
- Reduce prolonged leaf wetness and leave space for air to move.
- Damping down is a hot-weather tool, not a daily winter job.
- A circulation fan moves air but does not remove moisture by itself.
Expert Tip
Check the greenhouse early in the morning as well as in the afternoon. A comfortable midday reading can hide a night of dripping glass and wet leaves. Look at the plants, compost and thermometer together before changing anything.
What humidity should a greenhouse have?
There is no single ideal humidity for every greenhouse. Cucumbers, tomatoes, orchids and overwintered succulents do not all want the same conditions. Start with the plants you keep and avoid prolonged extremes.
Relative humidity describes how close the air is to saturation at its current temperature. As the air cools overnight, the percentage can rise without you adding water. Condensation forms when a surface is cold enough for moisture to collect on it.
That is why a percentage without a temperature or time of day is incomplete. Follow crop-specific advice and look for recurring problems, rather than chasing a number all day.
How do you measure greenhouse humidity?
Use a hygrometer in a representative place near the plants. Keep it out of direct sunlight and away from an open door, a heater outlet or recently wetted surfaces. Follow the instrument's placement instructions.
Vitavia Hygrometer costs £28. A maximum-minimum thermometer alongside it helps explain the day's highs and overnight lows.
Note morning and afternoon readings for several days. Check whether the same corner stays damp, pots are touching or the floor remains wet. A home greenhouse rarely needs a complicated monitoring system to spot those patterns.
How do you reduce high humidity?
Let moisture escape and reduce the sources of unnecessary water. Start with a safe air route through the greenhouse, using suitable vents and doors as the weather allows.
- Space plants so leaves are not pressed together or against the glazing.
- Water the compost when needed, preferably early enough for spills and wet foliage to dry.
- Empty unwanted standing water from trays and fix leaks.
- Remove dead leaves and spent flowers, especially where they collect between pots.
- Ventilate during suitable milder periods, checking the temperature needs of the plants.
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Roof vents and lower openings help exchange air. Our greenhouse ventilation guide explains their different roles and how automatic openers fit in.
A fan can help air move through a crowded canopy, but a fan in a sealed greenhouse simply circulates the same moist air. Ventilation also depends on outdoor conditions, so check what happens after opening up.
What should you do about morning condensation?
A little condensation on cool glazing is common. The concern is repeated dripping onto plants, leaves that stay wet and conditions favourable to mould.
Check watering time, plant spacing and whether insulation has blocked the air route. A cold frame or greenhouse packed for winter can need rearranging even when every pot fits.
Inspect affected growth rather than assuming all marks are caused by humidity. Our grey-mould guide explains what to look for and how to reduce conditions that encourage it.
A quick check before you act
- Wet leaves and dripping glass? Check ventilation, standing water and crowding.
- Wilted plants with dry compost? Water the roots and check excessive heat first.
- Wilted plants with wet compost? Inspect roots and pests; do not automatically add more water.
- Hot, dry air around moisture-loving plants? Consider damping down suitable floor surfaces and review shading.
How do you raise humidity safely?
In hot, dry weather, damping down suitable hard floor surfaces adds moisture as the water evaporates. Keep walkways safe and avoid water near electrical equipment. Stop adding water if it leaves the greenhouse persistently damp.
For individual humidity-loving plants, a suitable pebble tray can be useful. Keep the pot base above the water and clean the tray regularly. Do not stand every crop in water or routinely mist all foliage.
Watering compost supplies roots. Raising air humidity is a separate job and does not replace root watering.
Damping down can help raise humidity in hot conditions. Reduce it as the weather cools, so surfaces can dry before night.
Can tomatoes and cucumbers share the same greenhouse?
Yes, many home growers keep them together. Give both enough root space and air movement. Keep tomatoes from shading smaller plants and avoid cold draughts directly over tender cucumber growth.
A small greenhouse does not have perfectly separate humidity zones. Aim for a workable compromise: evenly moist roots, sensible ventilation and foliage that does not remain wet overnight. Our cucumber guide and tomato guide cover the individual crops.
Do you need a dehumidifier or humidifier?
Most hobby growers should improve ventilation, spacing and watering first. Specialist enclosed growing setups may need active humidity control, but equipment must suit the temperature, damp conditions and electrical installation.
Do not move an ordinary household appliance into a greenhouse without checking its suitability. A heat mat warms the root area; it does not control humidity throughout the structure.
Browse greenhouse monitoring and ventilation accessories for a defined need. Buying equipment before identifying the problem can leave the original damp corner unchanged.
How should your routine change in winter?
Plants use less water as growth slows, so check each pot before watering. Keep ventilation available during suitable spells, but protect tender plants from temperatures below their needs.
A warm greenhouse with wet foliage can still have disease problems. Equally, opening everything during a cold snap can damage plants. Use the weather forecast and your readings together, then adjust gradually.
Frequently asked questions
What is the best humidity for a greenhouse?
The right conditions depend on the plants and season. Use crop-specific guidance and monitor temperature alongside humidity rather than applying one target to every greenhouse.
How do I lower greenhouse humidity?
Improve air exchange and reduce unnecessary wet surfaces. Space plants, empty unwanted standing water and water appropriately, while protecting crops from cold.
Should I damp down the greenhouse every day?
No, use it when hot, dry conditions and the plants warrant it. Reduce or stop if the greenhouse stays damp or surfaces cannot dry before night.
Does a greenhouse fan remove humidity?
A circulation fan alone does not remove water from a sealed greenhouse. It moves air; moisture removal also needs suitable air exchange or specialist equipment.
Can a thermometer measure humidity?
Only if it includes a humidity sensor. A separate hygrometer measures relative humidity; check the instrument’s specification before buying.
Is condensation always bad for greenhouse plants?
No, some condensation on cool glazing is common. Repeated dripping, persistent wet foliage and mould are signs to review ventilation, watering and spacing.
