Summer is widely recognized as one of the most challenging seasons for leafy greens production in traditional (CEA) greenhouse facilities. The main reason? Temperature and intense radiation levels. Leafy greens are highly sensitive to root stress and disease when average 24-hour room temperatures exceed 21–22°C. On top of that, summer sunlight intensifies radiation exposure, putting further stress on plants if climate settings are not fine-tuned accordingly.
This guest article aims to offer practical, field-tested strategies for growers and operational teams who wish to maintain consistent production and avoid cultivation challenges during summer. The focus here is on traditional greenhouse cultivation, although the principles discussed are relevant and adaptable to both traditional and semi-closed greenhouse systems. We will cover:
- Climate control strategies and setpoints
- Shading and light diffusion
- Water management practices
- Disinfection
- Plant propagation
- Variety (genetic) selection
These recommendations are based on years of hands-on experience across various regions globally.
1. Climate Settings and Environmental Setpoints
One of the most critical aspects of summer cultivation is fine-tuning the climate control. The overarching goal should be to keep root temperatures below stress thresholds while also managing light, humidity, and air movement properly.
Radiation Management – During peak radiation hours, direct sunlight can cause significant plant stress, leading to lower transpiration efficiency, burnt leaf margins, and overall yield reduction. It is crucial to use shading strategies not just for light reduction, but to diffuse radiation uniformly across the crop. A “screen gap” strategy, where the shading & the secondary screen do not overlap each other, allowing a gap where air exchange can take place. This method prevents stagnant hot air from accumulating beneath the screen.
Ventilation Strategy – Effective fan ventilation helps in two key ways: by ensuring consistent CO2 distribution and by promoting transpiration. Good airflow is critical for leaf cooling and helps maintain a positive energy balance in the plant. During summer, maintaining high ventilation speeds and balanced negative pressure across the greenhouse is essential for proper climate management.
Fogging Systems – Fogging is a very effective method for cooling greenhouse air during hot days. It increases humidity and enhances the microclimate around the plant canopy. However, it must be used strategically. Over-fogging can lead to wet foliage, which is a serious concern for leafy greens, as it increases the risk of sunburn, bacterial spots, and fungal diseases. A well-calibrated fogging system should cool the air without wetting the leaves.
Bellow you’ll find a table with climate strategy values & setpoints for spring/ summer cultivation of leafy greens:Via Denis Laci / Agranom
2. Shading and Glass Coating
While internal shading screens are crucial, external glass coatings can further reduce radiation stress. These coatings help diffuse light, eliminate hot spots, and reduce the intensity of direct sunlight.
There are two main types of coatings:
- Diffuse coatings: Spread the light more evenly throughout the greenhouse
- Shading coatings: Reflect a percentage of incoming radiation
Depending on your geographic location and greenhouse orientation, combining both may yield the best results. Regular maintenance and reapplication are necessary during the summer cycle.
3. Water Management
Irrigation Water Temperature – Water temperature is arguably the most underestimated variable in leafy greens hydroponics. When water temperatures exceed 22°C, root performance begins to decline. Enzymatic processes slow down, and root respiration increases, causing oxygen deficiency and susceptibility to disease.
We recommend keeping irrigation water 3–4°C cooler than the ambient greenhouse temperature during the hottest periods. This thermal buffer helps cool root zones while the canopy may still experience high radiation and heat levels.
Solutions:
- Install industrial water chillers in the irrigation loop
- Use insulated water tanks to prevent heat absorption
Dissolved Oxygen (DO) Levels – As temperatures rise, water’s ability to retain oxygen declines. Low dissolved oxygen in hydroponic systems (especially in DWC) can lead to root suffocation, slower nutrient uptake, and disease development.
Maintain DO levels between 15–20 ppm. This can be achieved through:
- Nano-bubble generators
- Mechanical aerators
- Oxygen injection systems
These systems improve oxygen distribution throughout the nutrient solution, supporting healthy root development.
Water Recirculation – Still or stagnant water becomes a breeding ground for algae, biofilm, and pathogens. In DWC systems, ensure continuous water movement using submersible pumps and air stones. In NFT systems, aim for longer irrigation cycles and shorter intervals between irrigation events to keep the roots oxygenated and nutrient-fed.
Filtration & Biofilm Prevention Two levels of filtration should be standard:
- Pre-filtration: To remove physical particles
- Fine filtration: To remove biological contaminants
Additional UV sterilizers or ozone injectors may be included depending on water quality and system size.
Refer to our detailed guide on www.agranom.nl under “Water Management” for more information on filtration equipment combinations.
4. Disinfection Practices
In summer, maintaining a clean growing environment is not just good practice, it’s essential.
Clean Infrastructure – Between cycles, all NFT gutters and DWC floaters must be cleaned thoroughly. Remove old roots and scrub off biofilm using high-pressure water combined with hydrogen peroxide or food-grade disinfectants. If these residues are left untreated, they can become breeding grounds for Pythium and other harmful pathogens.
Disinfecting Irrigation Water Multiple technologies are available, such as:
- UV disinfection units
- Ozone generators
- Electrolyzed water systems
Refer to our detailed guide on www.agranom.nl under “Water Management” for more information on disinfection of equipment combinations.
5. Propagation
Healthy young plants are more resilient and require fewer inputs later in the crop cycle. Focus on building a strong root system from the start by:
- Ensuring proper climate and irrigation cycles
- Maintaining clean propagation systems
- Avoid extra transplant steps and unnecessary movements
- Start with clean and disinfected substrate and seeds
Weak or stressed seedlings are significantly more prone to root rot and canopy issues later in life.
6. Genetics: Choosing the Right Varieties
Many cultivation challenges can be avoided with the right varietal choice. Spring-summer varieties typically are:
- Stronger on temperature & high radiation stress
- Less flowering or morphological issues on long daylengths
- Resilience on Pythium and other root related issues
We advise growers to trial at least three different cultivars per season alongside their main commercial variety. This not only builds experience but also provides a fallback option in case the main variety underperforms due to unexpected weather or system issues.
Final Thoughts
While summer introduces several cultivation hurdles, these can be overcome through proactive climate control, smart water management, and strategic variety planning. Investing in proper cooling systems, disinfection routines, and varietal trials will go a long way in securing stable production and minimizing crop loss.
At Agranom, we are “Your Leafy Greens Specialist”, here to support you with practical solutions and expert advice.
