Editorial correction, 28 October 2026: Legacy placeholder material and unsupported universal settings have been replaced with the cited extension guidance. Published by Gardenia Organic (Organization). Human horticultural review is pending.
Creating the perfect environment for your plants to thrive is essential when managing a greenhouse. To achieve this, you’ll need to pay close attention to the temperature and humidity levels within your greenhouse, as these factors can significantly influence your plants’ growth and health.
It’s important to understand that the ideal temperature and humidity vary depending on the types of plants you’re growing and the season.
Temperature targets depend on the crop, growth stage and light conditions. Use crop-specific guidance and measurements at plant height rather than treating one temperature or humidity percentage as ideal for every greenhouse.
As you cultivate different plants throughout the year, it’s crucial to adjust temperature and humidity levels accordingly to ensure the best-growing conditions for your greenhouse inhabitants.
This way, you can help your plants thrive and enjoy the fruits of your labor all year round.
Ideal Temperature for Greenhouse Plants
Understanding the ideal temperature for your greenhouse plants is crucial to ensure their healthy growth.
For a crop-specific example, the New England Vegetable Management Guide describes greenhouse tomato daytime temperatures of 75–80°F (23.9–26.7°C), with ventilation or shading to keep them below 85°F (29.4°C). It gives night temperatures of 62–65°F (16.7–18.3°C) after sunny days and 60–62°F (15.6–16.7°C) after cloudy days. These are tomato production references, not universal greenhouse settings.
It’s always a good idea to research the specific temperature requirements for the plants you plan to grow in your greenhouse. This will help you create the most conducive environment for their healthy growth and development.
Ideal Humidity Levels for Greenhouse Plants
Managing the humidity in your greenhouse is essential for the well-being of your plants, as it can impact their growth and yield.
Relative humidity changes with temperature. UMass Extension explains that cooling surfaces can reach the dew point and collect condensation, increasing disease risk. Monitor humidity together with crop temperature and leaf wetness; a single percentage is not a universal target.
Humidity affects the transpiration rate and nutrient absorption of your plants. When humidity levels are too high, it can lead to reduced yields and encourage the growth of mold or mildew.
On the other hand, low humidity conditions can cause your plants to suffer from dehydration and inadequate nutrient uptake.
To maintain the desired humidity levels in your greenhouse, you can adopt various strategies. Some of these include:
- Proper Ventilation: Implementing an effective ventilation system in your greenhouse helps in controlling humidity levels by exchanging warm, moist air with cooler, drier air from outside.
- Heating: If the temperature inside your greenhouse is too low, your heating system can raise the temperature, which also helps to reduce humidity levels.
- Humidifiers: For situations where the greenhouse air is too dry, you can use a humidifier to add moisture and maintain an optimal environment for your plants.
As you monitor and adjust the humidity in your greenhouse, keep in mind that different plants might have specific humidity requirements.
Do some research about the preferred conditions for the specific plants you’re growing and consider creating separate zones in your greenhouse with varying humidity levels if necessary.
Controlling the Humidity
One way to control humidity is by using ventilation. By opening vents and windows, you can allow excess moisture to escape and fresh air to circulate, reducing humidity levels.
Another effective method is to use a dehumidifier. This device works by removing excess moisture from the air, which can be especially helpful in humid climates.
Additionally, you can use fans to circulate the air and prevent stagnant pockets of moisture. By monitoring and adjusting these factors, you can maintain optimal humidity levels for your plants to thrive.
Plan heating and ventilation together
Circulation fans move air within the greenhouse; exhaust ventilation exchanges it with outside air. UMass Extension recommends coordinated heating and ventilation when moisture needs to be removed without overcooling plants. Water early enough for foliage and surfaces to dry before night, and reduce standing water.
Greenhouse heating calculator
Structure, glazing and temperatures → heater output, summer CFM and energy cost.
Open full calculator · Calculation schema v2 · Sources checked 2026-10-28
Your estimate
- Envelope area and air volume
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- Temperature difference and U-value
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All results and reference quantities
- Conduction heat loss
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- Air-exchange heat loss
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- Required thermal output
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- Heater output with selected sizing margin
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- Fuel / electricity input power
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- Selected sensitivity range
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- Estimated cost per night
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- Estimated cost for selected days
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- Summer volume-exchange CFM
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- Floor-area reference CFM
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- Sensible heat-load CFM
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- Nominal fan and intake free area
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- Combined sidewall openings
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- Combined ridge openings
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- Snow water-equivalent mass / pressure
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Worksheet generation time appears after calculation.
Formula and worked example
Conduction: Q = U × envelope area × ΔT. Example: 100 m² × 3 W/m²K × 20 K = 6,000 W conduction only, before air exchange or other losses.
Air exchange: Q = 1.2 kg/m³ × 1,005 J/kgK × ACH × air volume × ΔT ÷ 3,600. Thermal output is conduction plus air exchange. Input kW = output kW ÷ efficiency. Cost = input kW × equivalent full-load hours × tariff. 1 W = 3.41214 BTU/hr; 1 imperial U = 5.67826 W/m²K.
The selected sizing margin (15% by default) is shown separately from the modeled operating cost. Solar gains, ground losses, changing weather and thermal bridges are not included. This estimate does not size wiring or certify heater suitability.
U-values: Palram twin-wall panel data (4/6/8/10 mm: 3.8/3.5/3.3/2.9 W/m²K); Texas A&M glazing and air-exchange estimates (single/double film: 1.15/0.70; single/double glass: 1.13/0.65 imperial U). Glass estimates are generic glazing values, not product-specific tempered-glass certification. Use the supplier’s whole-system U-value when available.
UMass natural ventilation guidance: combined sidewall openings and combined ridge openings should each be 15–20% of floor area. These are opening references, not a guaranteed flow. Ventilation alone cannot cool below outdoor dry-bulb temperature.
Read the winter greenhouse heating guide or open the standalone heating calculator.
Conclusion
Choose temperature and humidity controls for the actual crop and season, then check their effect with measurements. Use the calculator to compare stated heat-loss and ventilation assumptions; it cannot establish a crop prescription or certify the greenhouse structure.