Light Deprivation Greenhouses
If you are cultivating short-day crops that depend on light exposure times to signal growth stage changes, your crops greatly benefit from the use of light deprivation. Light deprived greenhouses allow cultivators to grow these types of crops all year round because they are not restricted by seasonal light availability. Light deprivation greenhouses (also called "light dep greenhouses" or "blackout greenhouses") are greenhouses that are equipped with black greenhouse plastic that is opaque. To ensure the greenhouse is 100% light-proof takes a little more accessorizing. Making sure that light dep plastic is pulled at the correct time is another challenge.
Roll-to-Peak Light Deprivation Greenhouses
There are a few different styles of light deprivation greenhouses. The first is the roll-to-peak light dep system that pulls tarps over the outside of the greenhouse, meeting at the peak of the roof and extending down the sides of the structure. This is also called external light deprivation because the blackout tarps are applied over the outside of the greenhouse. This does mean that light dep plastic is exposed to the elements and needs to be inspected for punctures, light leaks, and replaced when it is no longer reliable. External light deprivation systems can be retrofit to existing greenhouses. They are cheaper than internal light dep systems because they have fewer components.
Manual light deprivation greenhouse kits are the lowest in cost but are labor-intensive. Greenhouse staff needs to precisely and reliably pull the light dep plastic at the same time every day. If you have reliable staff that can make sure this is done correctly at the same time every day, manual light dep can be just as effective as automated light dep. However, manual light deprivation systems are best for smaller greenhouses. For large greenhouses, automated light dep will be significantly less labor-intensive.
When it comes to ventilating manual light dep greenhouses, you will need to manage your roll-up sides so that when they are up to allow ventilation they do not leak any light into the greenhouse. This means that you have to pull tarps to achieve a 12-hour dark cycle but remove the tarps after sunset so you can roll up the sides of the greenhouse to allow for ventilation. That means pulling light dep tarps four times per day instead of twice. It is critical for plants to have ventilation during the dark cycle or they can suffer from the stress of excess heat, too much CO2 accumulation, too much humidity, and a high risk for mold.
Automated light deprivation greenhouse kits allow you to put your light and dark cycles on timers and reduce associated labor dramatically. These greenhouse kits also come with automated ventilation that allows for superior climate management without the risk of light leaks that can damage plants. Since automated roll-to-peak light deprivation systems are motorized and placed on a controller, you get precise light dep timing and the ability to schedule light and dark cycles with significantly less labor. Unlike the manual light dep system, your automated blackout plastic is only pulled twice per day and it is done using motors on roll bars. The automated ventilation assures that heat, humidity, and CO2 does not build up during the dark cycle and reduces the risk of mold.
Internal Light Deprivation Greenhouses
The next style of light deprivation is the internal light dep greenhouse. Internal light deprivation greenhouse kits are the most expensive option but are also the highest quality and longest lasting. That is because you are building a greenhouse inside a greenhouse. The outer greenhouse is covered with clear greenhouse plastic, and the inner greenhouse has removable light deprivation plastic. The outer greenhouse plastic protects the light dep plastic from the elements so it has better longevity.
Internal automated light deprivation greenhouse kits by Hortitech Direct are motorized and controller operated for reduced labor. They feature automated ventilation to ensure plants stay cool and get enough fresh air, and are ideal for all-season greenhouses that operate year-round. If your location gets very cold and experiences snow in the winter, you can add on a greenhouse heater. Since these are more expensive light deprivation systems, most growers will want to operate them year-round to see the highest returns on their investment.
Lighting for Light Deprivation Greenhouses
Year-round greenhouse cultivation allows you to get the biggest return on your investment in a light deprivation greenhouse. This means that you may also wish to invest in greenhouse lighting. Using photosynthetically active lighting ("PAR lighting") like metal halide lamps, high-pressure sodium lamps, or LED grow lights means that your plants will get the light they need even when weather is cloudy, sunsets are early, or sunrises are late. Sometimes this type of lighting is referred to as "supplemental lighting." If you are going to operate your light deprived greenhouse year-round, grow lights will ensure that you can successfully mimic the sun. You won’t need to run grow lights as frequently as in an indoor grow and you’ll still be able to take advantage of natural sunlight. However, you will not be restricted to growing according to seasonal sun exposure.
Light Dep Greenhouse Climate Control
Another consideration to keep in mind is that while a light deprived greenhouse needs to be 100% light-proof, it still needs to have sufficient ventilation. It can get very hot and humid underneath blackout tarps, so it is a good idea to invest in automated ventilation. During the dark cycle, plants let out CO2 which accumulates around the canopy. Circulatory airflow ensures that air gets mixed and dispersed so heat, humidity, and CO2 do not create stressful conditions that encourage mold and pests. The cost of automated ventilation is really not that cumbersome if you consider the increased risks of crop failure that come with poor ventilation. Light traps are used to ensure that ventilation does not leak light. This offers more reliable light proofing than roll-up sides and manual light dep operation.
Light Deprivation Plastic for Greenhouses
One more thing to consider is what you will cover your light dep greenhouse with. Light dep plastic (also called “panda film,” “blackout tarps,” or “blackout cloth”) comes in a variety of thicknesses. Panda Film or 5 mil Black/White Greenhouse Film from Berry Plastics will be the cheapest option. However, these are thinner blackout cloths that will likely need to be replaced annually. The best light dep tarp material is 12 mil Woven Black/White Greenhouse Plastic by BTL liners. This thick and durable plastic will last for multiple years and be more resistant to tears, punctures, and weather exposure. It is the best and most durable light dep plastic which is why we pre-configure our light dep greenhouse kits with that option.
Final Thoughts on Light Dep Greenhouse Kits
If you are growing a high-value short day crop, a light deprivation greenhouse kit will allow you to grow more crop cycles in a year and permit you to grow year-round. While you will yield more plants this way, you will also benefit from investing in a higher quality greenhouse kit with automation. Light deprivation systems can do more harm than good if they are not properly installed and operated, so if you are not prepared to take on this investment it may be best to stick with a simpler seasonal greenhouse than jump into light deprivation systems. However, if you decide to grow year-round and invest more upfront, you will definitely be pleased with the increased earning potential of an all-season light dep greenhouse.