Which is Better for a Greenhouse: Glass or Polycarbonate?

Choosing the right material for your greenhouse is crucial to creating a thriving environment for your plants. In New Zealand, where weather conditions can vary widely, selecting the most suitable material—glass or polycarbonate—can make a significant difference in the performance and longevity of your greenhouse.

 

Overview of Glass and Polycarbonate

Glass has been the traditional material for greenhouses for many years. Its clear appearance and high light transmission make it a popular choice for gardeners who want a classic look.

Polycarbonate, a more modern alternative, is a type of plastic known for its durability, insulation properties, and impact resistance. It is becoming increasingly popular among greenhouse owners who want a practical, cost-effective solution.

 

Advantages of Glass for Greenhouses

  1. High Light Transmission: Glass provides excellent light transmission, allowing up to 90-95% of sunlight to reach your plants. This is particularly beneficial in areas with lower light levels or during shorter winter days.
  2. Aesthetic Appeal: A glass greenhouse has a timeless, elegant look that many gardeners find appealing. Its clear panels blend well with garden settings and add a classic charm to your backyard.
  3. Durability Against UV Degradation: Glass does not degrade or yellow over time when exposed to UV rays, maintaining its clear appearance for many years with minimal maintenance.

 

Disadvantages of Glass for Greenhouses

  1. Fragility: Despite its durability, glass can break or shatter under impact from hail, falling branches, or accidents. This fragility can pose safety risks, especially in areas prone to severe weather or if you have children playing nearby.
  2. Poor Insulation: Glass offers limited thermal insulation, which can result in higher heating costs to maintain a stable growing environment during New Zealand's colder months. The poor insulation can also lead to temperature fluctuations that may stress plants.
  3. Heavy and Expensive: Glass is heavy, requiring a stronger frame and support structure, which can significantly increase the cost of building and maintaining a glass greenhouse.

 

Advantages of Polycarbonate for Greenhouses

  1. Superior Insulation: Polycarbonate panels provide excellent thermal insulation, retaining heat more effectively than glass. This helps maintain a consistent internal temperature, reducing heating costs and creating a more stable environment for your plants.
  2. Impact Resistance and Durability: Polycarbonate is virtually unbreakable, making it highly resistant to impacts from hail, branches, or other debris. This durability makes it a safer option, especially in areas with unpredictable weather patterns.
  3. Light Diffusion for Better Plant Growth: Unlike glass, which allows direct sunlight, polycarbonate diffuses light, distributing it more evenly throughout the greenhouse. This diffused light reduces the risk of scorching plants and promotes uniform growth, especially for sensitive plants.
  4. Lightweight and Easy to Install: Polycarbonate is much lighter than glass, which means it requires a less robust frame and is easier and quicker to install. This reduces both the initial construction costs and ongoing maintenance efforts.
  5. Cost-Effective: Generally, polycarbonate greenhouses are more affordable than their glass counterparts. The reduced need for a heavy-duty frame and the material’s durability make it a cost-effective choice for both hobbyist and professional gardeners.

 

Disadvantages of Polycarbonate for Greenhouses

  1. Reduced Light Transmission: While polycarbonate allows sufficient light for plant growth, its light transmission rate (about 80-85%) is slightly lower than glass. This reduction is usually negligible for most plants but may affect very light-sensitive varieties.
  2. Aesthetic Considerations: Polycarbonate does not have the clear, classic look of glass. Over time, polycarbonate panels can become slightly discoloured or cloudy, which may not appeal to gardeners who prioritise aesthetics.
  3. Potential for UV Degradation: Although most polycarbonate panels come with UV-resistant coatings, prolonged exposure to the sun can eventually cause yellowing or degradation, requiring replacement after several years.

 

Glass vs Polycarbonate: A Comparison Table

Feature Glass Polycarbonate
 Light Transmission  90-95%  80-85%
 Durability  High (but can shatter)  Very high (virtually unbreakable)
 Weight  Heavy  Lightweight
 Insulation  Low  High
 Cost  High (material and frame costs)  Moderate to Low

 

Key Considerations When Choosing Between Glass and Polycarbonate

  1. Climate Suitability: In New Zealand, where temperatures can range from hot summers to cold winters, polycarbonate’s superior insulation is a significant advantage. It helps keep the greenhouse warm in winter and cooler in summer, providing a stable growing environment year-round.
  2. Budget Constraints: For those looking for a more budget-friendly option, polycarbonate offers significant savings not only in material costs but also in installation and maintenance. It requires a less sturdy frame, reducing the overall cost of the structure.
  3. Safety and Durability: In areas prone to severe weather, polycarbonate’s impact resistance is a crucial factor. Its ability to withstand strong winds, hail, and debris without breaking makes it a safer and more reliable choice.
  4. Plant Needs: If you grow plants that prefer diffused light and stable temperatures, polycarbonate is a better option. Its ability to evenly distribute light and maintain consistent temperatures can lead to healthier and more robust plant growth.
  5. Long-Term Considerations: While glass offers a classic appearance and high light transmission, its drawbacks in terms of fragility, insulation, and cost make it less practical for most modern greenhouses, especially for those seeking low maintenance and high durability.

 

Conclusion

While both glass and polycarbonate have their merits, polycarbonate stands out as the superior choice for most gardeners, particularly in New Zealand's varied climate. Its combination of excellent insulation, durability, and cost-effectiveness makes it ideal for creating a stable, efficient, and safe greenhouse environment.

Polycarbonate’s lightweight nature and ease of installation make it a practical option for both new and experienced gardeners. Its impact resistance ensures longevity and safety, reducing the need for frequent repairs or replacements.

For those looking to maximise the benefits of their greenhouse with minimal drawbacks, polycarbonate is the recommended choice. It offers the best balance between performance, cost, and practicality, ensuring your plants thrive in a well-regulated environment year-round.