Building or buying a greenhouse is an exciting project for any gardener. A greenhouse allows you to grow plants year-round and protect delicate seedlings and flowers from harsh weather.
When constructing or purchasing a greenhouse, one of the most important decisions is choosing the right covering material. Greenhouse plastic is the most common glazing option for home greenhouses. The plastic forms a transparent or translucent barrier that allows sunlight to enter while trapping heat inside.
There are several types of greenhouse plastic to consider. The main options are polyethylene film, polycarbonate panels, and acrylic sheets. Each material has advantages and disadvantages. This article will discuss the key factors to help you determine the best plastic for a greenhouse in your climate and for your gardening needs.
What to Look for in Greenhouse Plastic
Durability
First, assess the durability of the plastic. Greenhouse covers must withstand exposure to sun, wind, rain, snow, and hail. Durability equates to longevity. More durable plastics will last longer before needing replacement.
- Polyethylene films – These thin plastic sheets are inexpensive but less durable than rigid panels. Lifespans range from 1 to 4 years.
- Polycarbonate panels – Extruded or multi-wall polycarbonate sheets last 4 to 10 years. Polycarbonate is naturally UV resistant.
- Acrylic sheets – Acrylic is the most durable option, lasting up to 15 years. Acrylic resists yellowing from UV exposure.
Strength and Impact Resistance
The covering also needs to be strong and impact-resistant. Falling tree limbs, hail, and snow loads can damage weaker films.
- Polyethylene films sustain punctures and tears more easily than polycarbonate or acrylic.
- Polycarbonate panels are 200 times stronger than glass. This makes them very hail-resistant.
- Acrylic sheets are 10 times stronger than glass. Acrylic withstands heavy snow loads.
Light Transmission
Greenhouse plastic needs to allow sufficient light transmission for plant growth. Different plastics transmit light differently.
- Polyethylene films diffuse light well. Models are available with anti-condensate coatings to reduce water droplets.
- Polycarbonate panels lose some intensity but still transmit around 80% of light. The layered construction helps insulate.
- Acrylic sheets have the highest light transmission at over 90% transparency. This is closest to glass.
Insulation Value
The plastic glazing plays a vital role in insulating the greenhouse. The insulation value determines how well it traps heat.
- Polyethylene film has little inherent insulation value. Multiple layers can be used to improve heat retention.
- Polycarbonate panels have excellent insulation properties thanks to their multi-wall channels. The air gaps retain heat.
- Acrylic sheets have moderate insulation capacity. Acrylic with an aerogel layer boosts thermal performance.
Clarity and Light Diffusion
The appearance of the plastic is another consideration. Clarity determines how clearly you can see through the material. Light diffusion indicates how smoothly it transmits light.
- Polyethylene films often appear cloudy or frosted rather than crystal clear.
- Polycarbonate panels are reasonably transparent but disperse light somewhat.
- Acrylic sheets offer the greatest clarity and sharpest light transmission. Visibility is very clear.
Affordability
Finally, compare costs. Greenhouse plastic prices vary greatly.
- Polyethylene films are the most economical, starting around $0.15 per square foot.
- Polycarbonate panels cost $1 to $2 per square foot. Twin-wall polycarbonate is moderately priced.
- Acrylic sheets range from $2 to $4 per square foot. Extruded acrylic is more affordable. Cast acrylic runs up to $6 per square foot.
Other Material Differences
- Polyethylene sheets are flexible films. Polycarbonate and acrylic are rigid panels.
- Polyethylene and polycarbonate can be corrugated or pleated for added durability.
- Polycarbonate is available in a wide range of tints, colors, and diffusions. Acrylic and polyethylene come in fewer options.
- Acrylic can be bent and formed into domes and barrel vault shapes to suit some greenhouse designs. The other plastics do not bend.
Recommendations by Climate
The ideal greenhouse plastic depends partly on your climate conditions.
Cool Climates
In cool climates, insulation and heat retention are vital. Polycarbonate panels are often the best plastic choice for greenhouses in cold regions. The multi-wall construction provides excellent insulation. Polycarbonate also withstands heavy snow loads.
Acrylic sheets are another cold-climate option. While they don’t insulate quite as well, their high light transmission improves growth. Adding an interior thermal blanket can enhance heat retention in an acrylic glazed greenhouse. Avoid single layer polyethylene films.
Warm Climates
In warm regions, heat protection in summer is a priority. Acrylic sheets are a top recommendation due to their superior light transmission. This maximizes growth while preventing overheating. Their durability also resists damage from summer storms.
Polyethylene films work sufficiently well for short-term greenhouses in warm areas. Opt for UV stabilized, 6 mil films for 1 to 2 year longevity. Add shade paint or shade cloths to reduce temperatures during hot spells.
High Wind Regions
In zones with frequent heavy winds, impact resistance is paramount. Polycarbonate panels stand up best under pressure and provide excellent protection. If opting for less rugged polyethylene films, install sheets loosely so wind can blow through rather than rattling the structure. Sturdy greenhouse construction is also essential in high wind regions.
High Hail Areas
Hail-prone areas demand ultra-strong covers. Polycarbonate panels and acrylic sheets offer the greatest hail resistance. Polyethylene films will likely sustain major damage from large hail. Install polycarbonate or acrylic panels over a hail-proof framework and avoid glass options to limit damage.
High Sun Regions
For maximum light in predominantly sunny southern zones, acrylic glazing makes a top choice. Avoid heavily tinted or frosted polyethylene and polycarbonate films that further reduce light. Control heat in high sun with exhaust fans, shade cloths, and proper ventilation. Leave space between panels to enhance airflow.
High Humidity and Rainfall Areas
In humid climates, condensation control is important. Opt for polycarbonate or acrylic panels with specialized coatings that cause water droplets to sheet down the glazing. Improve airflow with vents and fans. Polyethylene films are prone to sagging and condensation buildup in wet environments.
Other Considerations
- Building codes – Some areas regulate plastic glazing. Check local ordinances before installing greenhouse covers.
- DIY vs professional installation – Rigid panels often require expert installation, while you can apply poly films yourself. Acrylic in particular may need pro help.
- Appearance – Polycarbonate offers a modern, sleek look. Acrylic appears glass-like. Poly films look more makeshift.
- Fire safety – Check codes for fire rating requirements. Polycarbonate is self-extinguishing while acrylic can burn.
- Chemical resistance – Acrylic withstands some chemicals, cleaners, and fertilizers that can degrade other plastics.
- Recycling – Look for recycled content and recyclability. Polycarbonate and acrylic sheets can often be recycled.
- Warranties – Opt for reliable brands and products that offer at least 10 year warranties.
Conclusion
The ideal greenhouse plastic improves plant growth while withstanding the elements. Seek sufficient durability, light transmission, insulation, and protection from impacts. Polyethylene films suit temporary structures. Polycarbonate excels in cold climates and resists hail. Acrylic provides the clearest light and best warmth in hot sunny regions. With the right glazing material, your greenhouse can thrive for many seasons to come. Consider your climate, budget, and needs when deciding on the best plastic for your greenhouse.
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