“Building a leafy greens facility starts with production goals and cultivation decisions, not technical specifications”

Building a greenhouse specifically designed for leafy greens requires integration between horticultural strategy and technical design. During the Leafy Hydroponics Event, Ronald Thijssen of Ammerlaan Construction provided a detailed walkthrough of the key considerations for constructing a high-tech greenhouse facility for leafy greens. Spoiler alert: Unfortunately, even in leafy greens, there's no one-size-fits all. But there is a guideline on where to start.

© Arlette Sijmonsma | VerticalFarmDaily.comRonald during the Leafy Hydroponics Event 2025

The growing concept
Based in the South of the Netherlands, Ammerlaan has been active in greenhouse construction since 1948, with experience spanning vegetables, soft-fruit, flowers, and increasingly, high-tech leafy greens projects.

According to Ronald, designing and building a leafy greens facility starts with production goals, not technical specifications. "The key principle is the growing concept. So before anything else, growers need to know: what kind of crop (variety choice(s), what kind of harvest weight, total harvest goal a year and what kind of production system they want. That determines the size and structure of the greenhouse," he explained. Growers must consider whether they want to produce baby leaves or full-head lettuce, whether they will do their own germination or outsource plant material, and what type of cultivation system they will use—NFT, floating raft systems (DFT), or mobile gutter systems. These decisions directly influence greenhouse layout, dimensions, infrastructure, and long-term operational planning.

Location
Location is another foundational element. Snow and wind load data influence structural requirements, while energy strategy hinges on available sources for heat, electricity, and CO₂. Access to high-quality well water is essential. "Rainwater is not enough. A well water sample needs to be taken early. We check for elements like iron content, which may need de-ironing filtration," Ronald said.

The greenhouse should be designed with the full project scale in mind, even if only one phase is being built initially. Sizing boiler systems, water treatment, and harvesting facilities for future phases avoids costly retrofitting. "It's not efficient to install a small boiler and then replace it later. Better to oversize at the start if expansion is planned," he added.

Choice of growing system determines technical layout. NFT and mobile gutters typically require trellis structures, while DFT systems require concrete basins. Each has structural and operational implications. For example, trellises in mobile gutter systems need to be specially shaped to handle the crop weight and facilitate drainage, while floating systems need reinforced foundations to support water-filled basins.

© Ammerlaan Construction

Ronald discussed greenhouse typologies: traditional, hybrid semi-closed, and full semi-closed. The differences are mainly in air management and energy control. Traditional greenhouses rely on natural ventilation. Hybrid models include fan-based systems with moderate air exchange capacities, while fully semi-closed systems use high volumes of mechanically moved air. However, high air exchange also means higher electricity use. "When you go up to 70 or 80 cubic metres per square metre per hour, that's a lot of electricity, so your energy pricing becomes very relevant," said Ronald.

For floating systems, air circulation is more difficult. Air tubes hang above the ponds, casting shadow and working against natural airflow, which moves from bottom to top. With NFT systems, air tubes can be placed more optimally to support vertical airflow. Fan selection also matters. Radial fans can build up more pressure and are more energy efficient, but cost more. Axial fans are cheaper and used for high-capacity air movement, particularly in semi-closed systems.

Cooling remains a technical and economic challenge. Mechanical cooling during peak radiation is often limited in effect, while costly in both capital and operating expenses. According to Ronald, "If you try to cool during the day, the impact is small. It's better to do it at night, when there's no sun radiation. You can bring down the 24-hour average temperature more effectively."

Evaporative cooling using pad walls is an alternative, but water quality must be monitored closely, particularly salinity. Options exist in paper or plastic, and some growers accept performance limitations during a few hot days per year to avoid large capital costs. "Some growers say: if I can run 350 days well, that's good enough. The other 15, I accept lower performance," said Ronald.

Light transmission is another central factor. For leafy greens, low-iron glass with high UV-A and UV-B transmission is now standard, as it enhances leaf colour and winter biomass. Diffuse glass can help spread radiation more evenly in hot regions, reducing peak temperatures, but lowers light transmission slightly. Anti-reflection coatings can help compensate. Ronald emphasized that whatever the coating or diffusion, "The base glass should always be low iron."

Shading and energy screens are typically triple-layered, placed at the top, middle, and lower levels of the greenhouse. This allows for flexible control of blackout, shading, and energy retention, with the ability to steer each function independently. Sidewalls can be built with fixed insulation panels or with glass/polycarbonate and movable wall screens. The choice affects upfront investment and operational flexibility.

Heating options include floor heating and monorail pipes. Coordination with air tubes is important to ensure heat transfer into the moving air. CO₂ can also be injected through the air system. Ronald warned not to overestimate heat transfer through the tubes: "Air in the tube loses heat as it travels, so we recommend using air that's just one or two degrees warmer than the greenhouse to maintain an even climate."

Water quality management
Water quality management is often underestimated. Ronald outlined a standard approach for drain water filtration: organic filters (cloth or tunnel), carbon filters to remove chemical residues, and ozone treatment to neutralize pathogens. Maintaining water at around 10°C and shielding storage from sunlight are basic requirements. Nano-oxygenation is also being adopted to stabilize water quality.

Lighting levels for leafy greens are increasing. For baby and teen leaves, intensities above 300 µmol/m²/s are becoming standard. LED installations must be dimmable and programmable with shifting red-blue ratios depending on cultivation stage. Maintenance infrastructure—glass lifts, internal service cars, roof platforms—should not be overlooked. "Maintenance doesn't make you money, but it prevents loss," Ronald noted.

In conclusion, unfortunately, there is no universal blueprint. "There's not one best solution. It depends on growing goals, location, energy strategy, and how much flexibility the grower wants," said Ronald. Growers are achieving stable production through various methods, and the main task is to align technical solutions with agronomic and business objectives from the start.