Humidity and Ventilation Management for Raspberries and Blackberries in Macro Tunnels

By: Corella Agro Greenhouses

Published On: February 18, 2026

Growing raspberries and blackberries in macro tunnels offers farmers a way to extend the growing season, protect crops from adverse weather, and improve fruit quality. However, managing humidity and ventilation inside these structures is crucial to prevent diseases, ensure healthy plant growth, and maximize yields.

Why Humidity and Ventilation Matter for Berries in Macro Tunnels

Raspberries and blackberries thrive in environments with balanced humidity and good air circulation. Excess humidity inside macro tunnels can create a breeding ground for fungal diseases like powdery mildew and botrytis, which damage fruit and reduce harvest quality. On the other hand, too much ventilation without humidity control can dry out plants and reduce fruit size.

Macro tunnels, typically made with plastic covers and metal or PVC frames, trap heat and moisture. Without proper ventilation, humidity levels can rise quickly, especially during warm days and cool nights common in coastal climates. Managing this microclimate is essential to:

• Reduce disease pressure

• Maintain optimal leaf transpiration

• Support pollination and fruit set

• Improve fruit shelf life and appearance

  
  

Understanding Humidity Levels for Raspberries and Blackberries

Ideal relative humidity (RH) for raspberries and blackberries ranges between 60% and 80%. Below 60%, plants may experience water stress, leading to smaller berries and weaker canes. Above 80%, fungal spores find ideal conditions to germinate and spread.

In coastal areas, humidity tends to be naturally higher, which increases the risk of fungal diseases inside macro tunnels. Monitoring RH with affordable digital hygrometers placed at plant canopy height helps growers adjust ventilation timely.

Ventilation Strategies for Macro Tunnels

Effective ventilation balances humidity control with temperature regulation. Here are some practical approaches:

1. Manual Side and End Roll-Up Systems

Many macro tunnels use plastic sheeting that can be rolled up on the sides and ends. Opening these flaps during the warmest parts of the day allows hot, moist air to escape and fresh air to enter. This simple method:

• Lowers humidity quickly

• Prevents heat buildup

• Improves air circulation around plants

  
  

Growers should monitor weather conditions and open flaps when outside humidity is lower than inside. Closing them before nightfall helps retain warmth.

2. Adjustable Roof Vents

As an option in a tunnel design, installing adjustable roof vents can improve vertical airflow. Warm air rises and escapes through these vents, pulling in cooler air from the sides. This natural convection reduces humidity without mechanical fans. Venlo plastic film, high technology film with perforated holes that allows trap hot air and humidity escape on the top of the structure, resulting more fresh air circulates helping promote healthy plant growth.

3. Use of Exhaust Fans

For larger tunnels or more controlled environments, low-power exhaust fans can be installed at one end, with intake vents on the opposite side. Fans help maintain steady airflow and humidity levels, especially on calm days when natural ventilation is limited.

4. Plant Spacing and Pruning

Good airflow starts with plant management. Keeping raspberry and blackberry rows adequately spaced and pruning excess foliage reduces humidity pockets around leaves and fruit. This practice complements ventilation efforts by allowing air to move freely within the canopy.

Monitoring and Adjusting Humidity

Regular monitoring is key to successful humidity management.

• Check RH levels twice daily, morning and afternoon

• Observe plant symptoms like leaf wetness or mold spots

• Adjust ventilation openings based on humidity readings and weather forecasts

  
  

Using simple data loggers or smartphone-connected sensors can provide continuous monitoring without high costs.

Additional Tips to Manage Humidity and Ventilation

• Watering practices: Avoid overhead irrigation inside tunnels. Implementing drip irrigation to keep soil moist without wetting foliage. Water early in the day to allow leaves to dry before evening.

• Mulching: Apply organic mulch to reduce soil evaporation and stabilize humidity near roots.

• Crop rotation: Rotate berry crops with non-host plants to reduce disease buildup in soil and air.

• Sanitation: Remove old leaves and fruit debris regularly to minimize fungal spores.

  
  

Case Example: Coastal Raspberry Farm Using Macro Tunnels

A raspberry farm located near coastline has successfully implemented an innovative system that combines side roll-up ventilation with an efficient drip irrigation method. This strategic approach not only optimizes the growing conditions for the raspberries but also enhances overall farm management. To monitor environmental conditions effectively, the farm installed advanced digital hygrometers positioned at canopy height, allowing for precise measurement of humidity levels directly within the raspberry plants’ growing environment. The decision to train workers on the importance of opening the tunnel sides when relative humidity (RH) exceeded the critical threshold of 75% was pivotal.

This proactive measure ensures that excess moisture is expelled from the tunnels, significantly mitigating the risk of fungal diseases that can devastate raspberry crops. The implementation of this simple yet effective system has yielded remarkable results, as evidenced by a significant 15% reduction in the incidence of fungal diseases when compared to previous seasons that lacked such ventilation control. This decrease in disease prevalence not only protects the health of the plants but also contributes to the overall sustainability of the farm's operations.

Furthermore, the farm has observed notable improvements in the quality of the raspberries produced. The size of the berries has increased, leading to a more appealing product for consumers, while the shelf life of the raspberries has also been extended. This enhancement in berry quality directly translates to increased market value, allowing the farm to capitalize on higher prices and potentially expand its customer base.

In addition to the immediate benefits observed in disease reduction and berry quality, the combination of side roll-up ventilation and drip irrigation fosters an environment that supports sustainable farming practices. By efficiently managing water use through drip irrigation, the farm conserves resources while ensuring that each plant receives the optimal amount of moisture required for healthy growth. This method not only reduces water waste but also minimizes the risk of water-logging, which can lead to root diseases.

Overall, the integration of these modern agricultural techniques has positioned the raspberry farm as a leader in innovative farming practices. The commitment to enhancing plant health and product quality through careful environmental control reflects a forward-thinking approach that could serve as a model for other farms in the region. The success of this farm underscores the importance of adopting technology and training in the pursuit of agricultural excellence, ultimately benefiting both the farmers and the consumers who enjoy the delicious fruits of their labor.