Light-deprivation greenhouses have revolutionized crop cultivation, giving growers unprecedented control over their plants’ growth cycle. By blocking out or manipulating the amount of light plants receive, growers can extend or shorten vegetative and flowering stages, allowing for multiple harvests in a single season. This technique especially benefits short-day crops that rely on specific dark times to trigger growth stage changes.
The Benefits of Light Deprivation
Light deprivation in greenhouse cultivation offers several advantages over traditional growing methods. Here are some key benefits:
Increased Yield: Light deprivation allows for multiple harvests in a single season, resulting in higher yield.
Controlled Growth Cycle: By manipulating the cycle of light and darkness, growers can control their plants’ vegetative and flowering stages, leading to more predictable and consistent growth.
Season Extension: Light-deprivation greenhouses enable growers to extend the growing season by creating the ideal light conditions regardless of the outside environment.
Pest and Disease Management: By controlling light exposure, growers can reduce the risk of pests and diseases that thrive in specific light conditions.
Higher Quality Crops: Light deprivation can enhance the quality of crops by influencing plant metabolism, which affects essential characteristics such as color, aroma, and flavor.
Internal vs External Light Deprivation Systems
Internal Systems
Internal light-deprivation systems are installed inside the greenhouse structure, providing a more streamlined and integrated approach to light control. These systems typically consist of blackout curtains or shutters mounted on tracks or rollers. While internal light-dep systems are more expensive to install than external systems, they are also more effective at blocking out light.
Here are some key characteristics of internal systems:
Custom Integration: Depending on the size and shape of your greenhouse, internal systems can be retrofitted into existing structures with relative ease. Small glass or rigid plastic greenhouses are typically easier to retrofit with internal light-dep systems.
Better Light Control: Internal light-dep systems reduce light reflection and refraction, making them more effective at blocking light. Growers can adjust specialized curtains or shades to optimize light intensity and wavelength.
Energy Efficiency: Internal light-dep systems can help to reduce energy consumption by trapping heat inside the greenhouse. Cold climate operations can benefit significantly from this effect.
Protection from External Factors: The greenhouse structure protects internal systems against external factors such as wind, hail, and extreme weather conditions.
External Systems
External light-deprivation systems are installed outside the greenhouse structure and involve blackout tarps or covers placed over the greenhouse and attached to the outside of walls and roof. External light-dep systems are less expensive to install than internal light-dep systems. Still, they can be less effective at blocking out light.
Here are some key characteristics of external systems:
Versatility: External systems can be used on many greenhouse structures, including hoop houses and custom-built greenhouses.
Affordability: External light-dep systems do not require modifications to the greenhouse structure, so they’re less expensive to install than internal light-dep systems. These cost savings make them popular for small-scale operations or growers on a budget.
Flexibility: External systems can be easily adjusted or removed to allow for natural light exposure during desired periods.
Potential for light leaks: Because external systems can be damaged by high winds, hail, and blowing debris, external light-dep systems are more prone to light leaks than internal light-dep systems.
Manual vs. Automatic Light Deprivation
Manual Systems
Manual light-deprivation systems require growers to manually open and close the blackout curtains or tarps to control light exposure. Manual light-dep systems are less expensive to install and maintain than automatic light-dep systems but are also more labor-intensive.
Here are some key characteristics of manual systems:
Cost-Effective: Manual systems are typically more affordable than automatic systems, making them a viable option for growers on a budget.
Flexibility: Manual systems allow growers more control over light exposure, as they can easily adjust the curtains or tarps according to their specific needs.
Labor-Intensive: Manually opening and closing curtains can be time-consuming and labor-intensive, especially for large-scale operations.
Inconsistency: Manual systems may not be as consistent as automatic systems, as they rely on human intervention to maintain the desired light cycles.
Automatic Systems
Automatic light-deprivation systems use sensors or timers to control the opening and closing of blackout curtains or shutters. Automated systems are more expensive to install and maintain than manual ones but require less labor.
Here are some key characteristics of automatic systems:
Time-Saving: Automatic systems eliminate the need for manual intervention, saving growers time and labor. This labor savings is especially valuable in large operations.
Consistency: Automatic systems can ensure more consistent light cycles, as they rely on sensors or timers to accurately control the opening and closing of curtains or tarps.
Higher Cost: Automatic systems are more expensive than manual systems, primarily due to the additional equipment and technology required.
Technical Complexity: Automatic systems may require more technical expertise to install and maintain, especially when integrating sensors and timers.
Greenhouse Design for Light Deprivation
There are many structure options to choose from for a light-dep greenhouse. The structure choice will depend on budget, space availability, and the specific requirements of the selected crops.
Here are three typical structure types for light-deprivation greenhouses:
Hoop houses:
Also known as high tunnels, hoop houses are a popular and cost-effective option for light-deprivation. These structures are typically made of metal hoops covered with greenhouse plastic.
Hoop houses offer flexibility in terms of size and can be easily customized to accommodate various crops. They are especially suitable for small-scale growers or those with limited space. Still, there are important considerations when evaluating this style for different types of light-dep systems.
Size: The size of the hoop house is an essential factor to consider when choosing a light-dep system. Smaller hoop houses are easier to equip with light-dep systems than larger ones.
Construction: The construction of the hoop house can also be a factor to consider. Hoop houses constructed with glass or rigid plastic can support more weight than fabric or other lightweight materials.
Location: The location of the hoop house can also affect the suitability of different types of light-dep systems. Hoop houses located in windy areas may require additional reinforcement to support the weight of the light-dep system. External systems may also need additional anchoring and tie-downs to keep covers in place.
Custom-Built Greenhouses
Custom-built greenhouses allow growers to design a structure that meets their needs and requirements. These greenhouses can be tailored during the design stage to accommodate light-deprivation systems. However, custom-built greenhouses with irregular shapes and configurations may require costly made-to-order systems.
Retrofitting Existing Structures
For growers who already have existing greenhouse structures in place, retrofitting them for light-deprivation can be particularly challenging; however, the economic benefits of an effective light-dep system may outweigh the extra expense.
Cost: Retrofitting a greenhouse with a light-dep system can be expensive, especially if you are installing an internal system.
Installation: Installing a light-dep system can be complex and time-consuming, especially in a large or complex greenhouse.
Greenhouse construction: Greenhouses constructed from lightweight materials may not be sturdy enough to support the weight of a light-dep system. A retrofit may require additional support beams for the greenhouse’s roof, walls, and foundation to help evenly distribute the weight of a light-dep system. In some cases, thicker materials for the frame and walls may provide enough support to prevent the greenhouse from sagging or collapsing, especially under snow loads, but an engineer should be consulted when evaluating reinforcement options.
