Surprisingly, light deprivation plays a major part in lots of greenhouses. This process is referred to as ‘light dep’, photoperiod manipulation, or photoperiodic control. This can be done through additional hours of darkness or manipulated by adding artificial lights when it would normally be dark. In light deprivation, blackout materials, like greenhouse covers, are used to simulate different environmental conditions. Simulating fall through shorter ‘daylight’ hours can convince plants to start producing flowers or fruits early. A greenhouse cover is pulled over across the building to block out the light and create a false nighttime. Alternating between more frequent periods and longer periods of dark is like the shorter days of fall. Accelerated flowering means that entire growing and harvesting periods can occur several times a year, rather than just in the fall.
Shorter days, and less light, stimulates hormone production in plants of the chemical called Apetala1. This hormone is what causes the production of flowers and fruits in plants.
A "short day" (long night) plant is one that needs a lot of darkness to grow. In the spring or fall, when the length of the day is less than 12 hours, short day plants produce blooms. Chrysanthemums, poinsettias, orchids, and strawberries are among the many spring and fall flowering plants that have short day lengths. Growers can mimic the light and darkness pattern of spring or fall by shortening the days by covering these plants with tarps like ArmorCover for at least 12 hours a day for many weeks over the late spring and early summer. This encourages summer blooming.
Numerous examined plant species have desirable responses to reduced light that have been meticulously documented. After purchasing this kind of equipment, you aren't constrained to only growing mums or poinsettias, either. Almost all plants that exhibit some sort of photoperiodic response may profit from light deprivation. A plant is unlikely to respond to any alteration of the photoperiod if it has been identified in several studies as being day neutral. Long-day plants typically require artificial illumination, but short-day plants, in particular, are likely to benefit from light deprivation.
You'll probably need to combine this technique with artificial illumination as well, unless a particular plant only requires a limited time of light deprivation to trigger flowering or growth. Many plants, such as poinsettias, require artificial illumination initially and then periods of darkness. Even while it may be more expensive to set up greenhouses to make use of both photoperiodic manipulation techniques, doing so is simpler than having to move substantial plant populations between various greenhouse configurations.
Light deprivation occurs for plants that need it as the day length changes naturally over the course of the year. If you need to control this process and make days seem shorter at random times instead, blocking out the light is the main method. This can be accomplished by:
Covering the entire greenhouse with a layer of light blocking tarp, shade cloth, or other materials
- Building smaller enclosures within the greenhouse
- Masking plants individually with small covers
- Shutting off artificial lighting
Light deprivation isn’t useful for every greenhouse crop, but it is widely used for annual bedding plants and seasonal decorations. Tricking plants into thinking it’s a specific time of year is a valuable tool for triggering all sorts of desirable behavior, like flowering.
Pre-existing greenhouses are fairly easy to convert into light dep structures. Metal and wood frames are secure enough to handle the weight of additional layers of light deprivation material. If extra structure is needed, additional internal posts can help bolster your greenhouse, allowing it to bear the weight of the new cover.
Tarps can be easily fabricated by BTL to fit any particular specification that fits your needs. See BTL’s ArmorCover and ArmorClear for more details.
Greenhouse covers can be manually put on and taken off, or automated to do so with the push of a button, or the setting of a timer. An automated system to pull out and draw back the cover will need its own structure to stand on if the original building is not strong enough for the additional weight. Automation requires some expense, but it's a safer way to move your cover, rather than removing and folding the material by hand. It also allows for exact timing, rather than relying on people and their unpredictable schedules. You’ll want a flexible material that is resistant to UV penetration and degradation. It needs to be durable in order to withstand frequent folding and unfolding.
To keep bugs out and promote natural airflow through the greenhouse, the entrance door and neighboring backdoor on either end of the green or hoop house are built of screen. There are also two exhaust fans set up, one at the far end drawing in fresh air and the other pushing air out. While being covered by our ArmorCover product might help to reduce humidity levels, don't overlook the need of airflow for ensuring optimum ventilation. Extra materials insulating the greenhouse will mean increased temperatures and more humid conditions, requiring increased ventilation.
As long as the roof has a smooth slope so that it won't catch the light dep cover when it is placed and removed, the greenhouse's frame can be made of wood. Doors may easily be cut out of the poly layer and attached to a wooden door frame with Velcro. The only parts of this design that need wood are the front and back ends. The hoops can be constructed of steel or PVC. Along the sidewalls of the greenhouse, a wood backing is also utilized to hold the hoop structure in place, but the use of bolted-down brackets that hold each individual hoop in makes for a simpler design. On top of leveled gravel, a weed-barrier geotextile is frequently used as the floor. Small circulation fans also move air within the greenhouse, and a dehumidifier keeps humidity low.
