Regardless of whether you need to cover an entire purpose-built structure or just a small enclosure inside a greenhouse, you’ll need a light deprivation cover you can trust. If the material fails or breaks down in the middle of a cycle, the crop inside could be damaged or lost entirely. Bedding plants, in particular, are very sensitive to fluctuations in light levels from low quality covers that let more lumens through than expected. Choose a cover material that truly controls light transmission and provides years of reliable service with these tips and hints.
Amount of Light Blocking
Not all light dep covers and tarps are designed to actually block light completely. Many are better categorized as deep shade cloths because they only block 70% to 80% of light transmission at most. 100% light transmission blocking is challenging to achieve with a woven material, but non-woven materials can definitely provide this kind of light control. These kinds of tarps are commonly referred to as total black out light deprivation covers. This refers to a total control of light transmission for true night extension rather than just growth control through irradiance limitation. If you need to do more than just reduce the intensity of the light, make sure you’re buying a cover designed for black out use.
Moisture and Air Circulation
Greenhouses already suffer from high moisture levels and sluggish air circulation, and unfortunately adding a layer of light dep cover doesn’t help much. When building small enclosures within a larger greenhouse, it’s particularly easy for the space to become extremely humid and encourage plant diseases. Breathable light deprivation covers are recommended for this kind of application. However, these woven and porous materials can’t be used on the exterior of a full greenhouse because they’re too absorbent and prone to tearing. Keep the breathable light-blocking covers for interior use and stick to more durable materials when covering a section of the exterior or a whole greenhouse at a time.
Heat Accumulation
Any time you enclose a greenhouse or a smaller section in a thick layer of dark colored material, you’re sure to increase the heat. Since greenhouses already accumulate a lot of heat, the extra thermal effect of a light dep cover can push the envelope and damage sensitive plants. Using light deprivation covers in winter only could help. Yet, that only works well in the Southern hemisphere since nights are already long in the Northern hemisphere during that time of year. Look for materials designed to minimize heat gain through the use of reflective or white outer surfaces, venting slits, or texture to reduce heat absorption. Increasing ventilation may be all you need to compensate for the extra heat.
Woven vs Non-Woven
Woven light deprivation covers are popular because they’re inexpensive to produce, lightweight, and flexible for easy removal. However, the woven material is naturally weak for the very purpose of light deprivation since each woven piece is prone to moving to create gaps that let light through. Non-woven materials, made with calendaring and other related techniques, are the only ones that can truly claim to achieve 100% black out conditions. When photoperiod control is essential to triggering flowering or a harvest, stick with the more durable and reliable non-woven cover materials only.
Reinforcement
Regardless of the specific cover you choose for light deprivation, look for a material that features a reinforced design. Reinforced greenhouse covers include a special layer of scrim tape designed to keep the material from tearing, folding, or bunching as you move it back and forth. Since most light deprivation covers are removed and replaced repeatedly, over the course of a cycle, crack and tear resistance is essential for these materials. Don’t settle for non-reinforced light deprivation covers when reinforced products are available from BTL Liners.
Material Options
The single most important decision you’ll make when selecting a light deprivation cover is its material. Some materials can handle daily exposure to intense sunlight and constant movement back and forth, while others simply break down and crack within a few months of use. Your options rated from best to worst include:
- Reinforced polyethylene (RPE), the material that offers the best combination of UV resistance, wear and tear durability, and light transmission control. It’s a non-woven material that can actually provide 100% total black out conditions, and it’s going to last the longest in a challenging situation such as covering over a greenhouse exterior.
- Low density polyethylene (LDPE), which isn’t as durable as RPE but at least has the flexibility to withstand constant removal and replacement over the greenhouse. It’s prone to UV damage over time, even when treated to resist sun damage.
- High density polyethylene (HDPE), which is too stiff and hard to fold to easily use as a light deprivation cover. The heaviness of this material also increases the chance of damage as it’s dragged over a greenhouse multiple times a day. However, it does offer slightly better UV resistance and longevity than some other materials.
- Polyvinyl chloride (PVC), a common material used for all sorts of flexible polymer sheets. It’s weaker than any kind of polyethylene when it comes to UV resistance, and PVC that’s treated for sun exposure may leech out chemicals that interfere with plant growth. While this material is flexible, it’s weak against wear and tear that comes with moving a light dep cover around all the time.
- Ethylene propylene diene terpolymer (EPDM), a thick and stiff rubber material that is simply too heavy to consider putting on top of a greenhouse. Even if the structure can handle the extra weight, it’s too stiff to conform to a curved or angled shape and provide useful light blocking. Leave the EPDM for other purposes like roofing and stick to RPE when choosing a material for light dep covers.
If all these considerations are a little overwhelming, BTL Liners is happy to help make the process even easier. Simply call us to discuss your needs for a light deprivation greenhouse and we’ll guide you to the right products. If you haven’t built the greenhouse yet, we can provide both the light transmitting clear glazing cover and light deprivation tarps to give you complete control over the day length inside the structure.
