Greenhouse plastic, or glazing material, transmits light necessary for plant growth while trapping solar energy to maintain warmth inside the structure. The lifespan of this covering is highly variable, depending on the type of polymer used and the specific environmental conditions it faces. Understanding these materials and the forces that cause them to break down is important for planning a long-term gardening structure.
Common Materials and Their Durability
Polyethylene (PE) film is the most frequently used material for greenhouse coverings, valued for its low cost and flexibility. Untreated, standard PE film is highly susceptible to ultraviolet (UV) light degradation and may only last one to two years before becoming brittle. To combat this rapid deterioration, most modern greenhouse-grade PE is UV-stabilized, extending its service life to a typical range of four to six years.
UV-stabilized polyethylene often uses a multi-layer co-extrusion process, incorporating additives to improve performance characteristics like light diffusion and anti-condensation properties. While PE is the most affordable option, its flexibility makes it more prone to tears and punctures over time compared to more rigid alternatives.
Polyvinyl Chloride (PVC) film offers a moderate lifespan, typically lasting five to seven years when properly UV-stabilized. PVC is naturally more durable than PE and provides good heat retention. However, it tends to become opaque or yellow over its service life, reducing the amount of usable light reaching the plants.
For the longest lifespan, polycarbonate is the standard choice, often used in rigid, multi-wall panels. These panels are highly resistant to impact and can maintain structural integrity for ten to fifteen years, with premium options lasting up to twenty years. The higher initial cost is justified by its superior insulation and durability, reducing the need for frequent replacement and supplemental heating.
Environmental Factors That Shorten Plastic Life
Ultraviolet (UV) radiation is the single most destructive environmental factor affecting the longevity of all plastic coverings. High-energy UV light breaks down the long polymer chains, a process known as photodegradation. This breakdown causes the material to lose elasticity, leading to yellowing, cloudiness, and eventually, embrittlement and failure.
The constant cycle of heating and cooling stresses the material, a process called thermodegradation. Temperature extremes, particularly intense heat build-up inside a closed greenhouse, cause the plastic to repeatedly expand and contract. This thermal cycling weakens the film over time, making it more susceptible to cracking, tearing, and mechanical failure.
Chemical exposure from common agricultural practices can rapidly reduce the expected lifespan of UV-stabilized films. Agrochemicals, particularly sulfur used for pest and disease control, react negatively with the embedded UV stabilizers. This reaction neutralizes the protective stabilizers, leaving the polymer vulnerable to photodegradation and causing a significant loss in mechanical strength and elasticity.
Chlorine-based cleaning agents or pesticides containing halogen compounds are extremely aggressive toward many types of plastic film. Even physical stress from wind, snow loads, or abrasion against the greenhouse frame can also compromise the covering. Wind flap constantly rubs the plastic against the frame, creating weak points that lead to premature tearing.
Maximizing the Lifespan of Your Covering
Proper installation techniques are fundamental to ensuring the plastic covering reaches its maximum potential lifespan. The film must be tensioned correctly to prevent excessive movement or “flapping” in the wind, which causes structural fatigue and abrasion. It is also important to ensure the plastic does not contact sharp edges, rough surfaces, or untreated wooden framing, as these elements accelerate wear and introduce chemical degradation.
Regular, gentle maintenance helps preserve the material’s light transmission and overall integrity. Cleaning should be done with mild soap and water, avoiding harsh chemical cleaners that contain chlorine or abrasive compounds that could damage UV-protective additives. Maintaining proper ventilation is also important to manage internal humidity and reduce chemical residues condensing on the film’s inner surface.
The covering signals the end of its useful life through several visual and physical changes. Growers should watch for visible yellowing or cloudiness, which indicates that UV stabilizers are breaking down and light transmission is compromised. A loss of elasticity, making the film feel stiff or brittle, is a physical sign that the polymer chains have degraded and the plastic is prone to tearing. Replacing the covering once these signs appear prevents catastrophic failure and maintains optimal light conditions for plants.