Covering a greenhouse with plastic sheeting creates a controlled growing environment, offering protection from harsh weather and allowing for precise climate management. The plastic skin regulates temperature, humidity, and light transmission, making its selection and installation a foundational step in successful greenhouse operation. This guide provides a detailed process for selecting materials, preparing the frame, and executing installation to maximize the lifespan and effectiveness of your structure.
Selecting the Right Sheeting Material
The choice of covering material directly influences the durability of the greenhouse and the quality of light reaching your plants. Standard coverings are typically polyethylene (poly film), measured by thickness in “mils.” Six mil is the industry standard for longevity and strength, and this clear film is commonly treated with UV stabilizers to prevent premature degradation from sunlight exposure, which causes the plastic to become brittle and yellow.
For growers seeking maximum resilience, a woven polyethylene material offers exceptional puncture and tear resistance, making it suitable for areas prone to high winds or hail. Selecting a covering with anti-drip additives is also beneficial, as this treatment reduces the surface tension of condensation. This causes water vapor to run down the sides instead of dripping onto the plants, which helps minimize the risk of plant diseases.
The material’s thickness and composition also affect light transmission; for instance, a nine-mil or twelve-mil plastic offers greater strength but slightly reduced light penetration compared to a six-mil film. Furthermore, some films include infrared (IR) additives designed to trap heat inside the structure at night, significantly improving temperature stability during cooler periods. Making an informed material choice based on your regional climate and desired lifespan is the first step toward a functional greenhouse.
Preparing the Greenhouse Frame
Before unrolling any plastic, the frame must be meticulously prepared, as neglecting this step causes premature plastic failure. First, thoroughly inspect the entire structure for any sharp edges, protruding screws, or splinters; wooden frames must be sanded smooth. Metal surfaces should be cleaned of dirt, rust, or debris, ensuring all structural elements are secure and stable.
A crucial preparatory measure is applying anti-hot spot tape, also known as frame lagging tape, to all parts of the frame that will contact the plastic. This white, adhesive-backed foam or felt material reduces abrasion and prevents heat degradation. Metal and wood surfaces heat up significantly in direct sunlight, and this localized heat transfer can chemically break down the polyethylene, shortening the film’s lifespan.
The tape’s white color actively reflects light and heat away from the contact points, keeping the plastic cooler. If using a wooden frame, ensure it is treated with a non-oily preservative, as certain chemicals and resins from untreated wood can react poorly with the polyethylene film. Applying the tape to all intermediate hoops and end-wall edges ensures a protective barrier is in place before the cover goes on.
Step-by-Step Installation Process
Timing the installation correctly is paramount, requiring a calm day with minimal wind (ideally less than five miles per hour) and temperatures between 59 and 70 degrees Fahrenheit. Installing the plastic during warm weather is beneficial because the material is more pliable and will slightly expand, allowing it to be stretched tight. As the temperature drops, the plastic contracts, pulling the cover even tighter against the frame.
The process begins by unrolling the plastic film along the length of the greenhouse, often referred to as the “blanket” method, and centering it precisely over the structure. For larger greenhouses, the film is usually folded to facilitate unrolling; one end should be secured temporarily to act as an anchor point. Using ropes thrown over the peak or long push brooms to lift, the film is carefully pulled over the frame, ensuring it remains centered and does not drag across sharp ground surfaces.
Once the plastic is draped over the entire structure, a small crew should temporarily secure one end, often the baseboard of an end wall, using clamps or a short section of wooden batten. Moving to the opposite end, the crew must pull the plastic tightly to remove major wrinkles and achieve initial tension. It is best to focus on stretching the plastic lengthwise along the structure first, eliminating slack in that dimension before tackling the width.
The plastic should be pulled taut enough to remove all large wrinkles, preventing the film from flapping in the wind, which causes wear and tear. Avoid excessive over-stretching, however, as this can lead to tearing, especially in cold weather when the material shrinks. Use stable ladders or lifts when working at heights, and coordinate the pulling effort to maintain even tension across the entire surface.
Securing and Sealing Edges
With the plastic pulled tight, the next phase is the permanent attachment and sealing of the perimeter. A highly effective and reusable method involves a spring-lock system, which consists of an aluminum channel screwed to the frame and a bent, stainless steel “wiggle wire” that locks the plastic securely into the channel. This system allows for easy removal and reinstallation when replacement is needed.
Alternatively, a simple and cost-effective method is to secure the plastic using wooden battens or lath strips over the film, screwing them into the frame’s baseboards and end-wall studs. Regardless of the method, the plastic should be secured by working from the center of each side outward, maintaining constant tension to smooth out any remaining wrinkles. For end walls, the plastic is pulled tight, and the excess is trimmed after permanent attachment.
A tight seal is necessary for maintaining the internal climate and preventing drafts, which negate the insulating properties of the plastic. Corners and gables should be sealed by folding the plastic neatly and securing it tightly into the channel or under the batten. Use silicone sealant or heavy-duty tape to close any small gaps. Finally, openings for vents and doors require a clean cut and a secure seal around the perimeter of the frame to prevent air leakage while ensuring accessibility.