Greenhouse Humidity Management: Core Significance, Methods and Supporting Measure

8 Scientific Dehumidification Methods: Operation Points and Application Scenarios

1. Regular Ventilation: Basic Dehumidification Method with Temperature Balance Consideration

• Core Principle: Through air circulation, discharge the high-humidity air inside the greenhouse and introduce dry outdoor air to reduce the humidity inside the greenhouse.
• Operation Details:
  • The timing of ventilation must be strictly controlled. Priority should be given to noon or afternoon on sunny days when the outdoor temperature is above 15℃ (avoid ventilation in the early morning, evening, and cold weather to prevent a sudden drop in the greenhouse temperature);
  • Adopt a "gradual" operation during ventilation: first open the top vents, then open the side vents after 15-20 minutes. If it is monitored that the temperature drop rate inside the greenhouse is >2℃ per hour, the vents should be timely reduced or closed to prevent crops from suffering from low-temperature stress;
  • In low-temperature seasons, "short-term and frequent ventilation" can be adopted, such as ventilating 2-3 times every noon for 10-15 minutes each time, to reduce humidity accumulation while ensuring the temperature.

2. Optimized Light Transmission Management: Dual Synergy of Temperature Increase and Dehumidification

• Core Principle: Sufficient light can increase the temperature inside the greenhouse. For every 1℃ increase in temperature, the relative air humidity decreases by approximately 5%-8%. At the same time, dehumidification can be accelerated with ventilation.
• Operation Details:
  • Clean the greenhouse film regularly to ensure that the light transmittance is increased by 10%-15%;
  • Select greenhouse film materials with excellent light transmittance, such as PO films (with a light transmittance of over 90%, as well as aging resistance and anti-fogging properties). Compared with ordinary PE films, they can reduce the condensation phenomenon inside the greenhouse and indirectly lower the humidity.

3. Temperature Increase for Dehumidification: Targeted Regulation to Meet Crop Temperature Needs

• Core Principle: By actively increasing the temperature, the saturated air humidity is improved, and the relative humidity is reduced. At the same time, it meets the temperature needs of crop growth, which is especially suitable for low-temperature and high-humidity seasons.
• Operation Details:
  • Application Stage: It is applicable when crops enter the adult plant stage (with certain stress resistance), and should be avoided in the seedling stage (seedlings have poor tolerance to high temperatures);

4. Rational Watering: Controlling the Source of Humidity from the Root

• Core Principle: Watering is the main source of increased humidity inside the greenhouse (the humidity inside the greenhouse can rise sharply by 15%-20% after a single watering). Scientific watering can reduce water evaporation and humidity accumulation.

5. Full Plastic Film Coverage: A Key Measure to Block Soil Evaporation

• Core Principle: Plastic films can effectively block soil water evaporation, reducing evaporation by 60%-70%, which is an "efficient method" to reduce the air humidity inside the greenhouse.

6. Intertillage and Soil Loosening: Physically Blocking Soil Water Evaporation

• Core Principle: Through intertillage, the surface soil capillary is cut off, preventing deep soil water from rising to the surface for evaporation. At the same time, it improves soil aeration and promotes root growth.

7. Natural Material Moisture Absorption: Low-Cost Auxiliary Dehumidification Method

• Core Principle: Utilize the moisture absorption properties of materials such as straw, wheat straw, and quicklime to absorb water vapor or fog droplets in the air inside the greenhouse and reduce local humidity.
• Operation Details:
  • Material Selection and Use:
    • Straw/Wheat Straw: Cut dry straw or wheat straw into 10-15 cm segments, and spread them evenly between crop rows (with a thickness of 5-8 cm). The dosage per square meter is about 1 kg, which can absorb 1.5-2 times its own weight in water. After rotting, it can be used as organic fertilizer to improve the soil;
    • Quicklime: Put quicklime into breathable cloth bags (5-10 kg per bag), and hang them in areas with high humidity inside the greenhouse (such as the corners of the greenhouse and near the vents). Place 1 bag per 20 square meters. Quicklime will agglomerate after absorbing moisture and needs to be replaced in a timely manner (usually once every 7-10 days);
  • Precautions: Avoid direct contact between quicklime and crop roots or leaves (it is corrosive). For straw/wheat straw, select dry materials without mildew to prevent the introduction of pathogens.

8. Optimization of Thermal Curtain Materials: Reducing Condensation and Lowering Humidity

• Core Principle: Selecting thermal curtain materials with good moisture permeability and absorption can prevent condensation on the inner surface of the greenhouse film, avoid dew dripping onto crop leaves, and at the same time achieve a thermal insulation effect.

Supporting Measures for Humidity Management: Monitoring and Dynamic Adjustment

1. Humidity Monitoring: Install temperature and humidity sensors inside the greenhouse (it is recommended to install 1 sensor per 500 square meters, hung at the same height as the crop canopy) to monitor the relative air humidity in real time. When the humidity exceeds the upper limit suitable for crops, start dehumidification measures in a timely manner;
2. Crop-Specific Adjustment: Different crops have different humidity requirements (for example, the suitable humidity for cucumbers is 70%-80%, and that for tomatoes is 60%-70%). The dehumidification plan should be adjusted according to the type of crops grown to avoid a "one-size-fits-all" approach;
3. Seasonal Adaptation: In the high-temperature and high-humidity summer, focus on dehumidification through ventilation and light transmission; in the low-temperature and high-humidity winter, focus on dehumidification through temperature increase, plastic film coverage, and natural material moisture absorption, while balancing thermal insulation and dehumidification.

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