fbpx
Home Agriculture Glass Greenhouses vs. Polycarbonate: Choosing the Right Covering for Commercial Greenhouses

Glass Greenhouses vs. Polycarbonate: Choosing the Right Covering for Commercial Greenhouses

Boosting yields and cutting costs are critical for any commercial greenhouse operation. A key factor in achieving this is selecting the optimal covering material. This guide provides a comprehensive comparison of glass greenhouses and polycarbonate greenhouses, empowering you to make an informed decision.

Commercial glass greenhouses

Light Transmission and Diffusion

Sunlight is the engine of plant growth, and your greenhouse covering significantly influences the amount and quality of light reaching your crops.

  • Glass greenhouses excel at light transmission, allowing maximum sunlight penetration – often exceeding 90% . This is especially valuable in regions with limited sunlight or for crops with high light demands. 
  • Large Polycarbonate greenhouses offers good light transmission, typically around 80-85% depending on the thickness and structure, but with a focus on diffusion. This creates a more even distribution of light, reducing shadows and potentially benefiting plants that thrive in less intense, indirect light. 

Why is Light Diffusion Important?

Light diffusion ensures that light reaches all parts of the plant, promoting even growth and preventing leaf scorch. Polycarbonate’s diffusive properties can be particularly beneficial for crops that are sensitive to intense direct sunlight.

Durability and Impact Resistance

Greenhouses are exposed to the elements, so durability is a key factor.

  • Polycarbonate is incredibly strong and impact-resistant, withstanding hail, strong winds, and accidental impacts without shattering . This makes it a durable and safe option, especially in areas with harsh weather conditions.  
  • Glass greenhouses, while traditionally known for their elegance, can be more susceptible to breakage. However, modern tempered glass offers significantly improved impact resistance, withstanding pressures of up to 200 psi , making it a more viable option for commercial growers concerned about breakage.  

Large Glass Greenhouse can expose to danger to snowfall

Is Tempered Glass Greenhouses Worth the Investment?

Tempered glass is more expensive than standard glass, but its increased strength and safety can be worth the investment, especially in areas prone to hail or strong winds.

Insulation and Heat Retention

Maintaining optimal temperatures within the greenhouse is crucial for plant growth and energy efficiency.

  • Polycarbonate, particularly multi-wall panels with their insulating air pockets, offers excellent insulation . This can lead to significant energy savings – up to 25% of operational costs – and more stable temperatures for your crops. An 8mm thickness is recommended for sidewalls and 10mm for the roof . 
  • Glass greenhouses generally have lower insulation values than polycarbonate, potentially leading to higher heating costs in colder climates. However, advancements in glass technology, such as double glazing, can improve insulation and reduce heat loss.

How to Keep a Large Glass Greenhouse Warm in the Winter

Supplemental heating systems are often necessary to keep a glass greenhouse warm in the winter. These can include forced-air heaters, radiant heaters, or even geothermal heating systems. Proper ventilation and insulation are also crucial to minimize heat loss and maintain a consistent temperature.

Learn more – read “Choosing the Right Greenhouse Heater: A Comprehensive Guide for All Growers”

Polycarbonate Plastic and Glass Cost and Maintenance for Greenhouses

Budget is always a factor in commercial greenhouse operations.

  • Large polycarbonate greenhouses typically have lower upfront costs than large glass greenhouses . Polycarbonate panels are generally less expensive than glass (around $0.12 per square foot compared to $2-$2.50 for glass), and installation can be easier and less labor-intensive due to the lighter weight of the material.
  • Glass greenhouses have a higher initial investment, but they can be more cost-effective in the long run due to their longer lifespan (40-50 years for glass vs. 10-25 years for polycarbonate) and lower maintenance requirements.

Cost-Effective Glass Replacement Options

While replacing broken glass panels can be expensive, there are cost-effective options available. Salvaged glass from demolished buildings or old windows can be a viable alternative, offering significant cost savings compared to purchasing new glass panels.

UV Protection

UV radiation can have both beneficial and harmful effects on plants.

  • Polycarbonate generally blocks most harmful UV rays, protecting plants from potential damage while still allowing sufficient light for photosynthesis. 
  • Glass greenhouses allow some UV transmission, which can be beneficial for certain plants that require higher UV levels for optimal growth . However, for UV-sensitive plants, additional shading or UV-filtering coatings may be necessary. 

What Type of Glass is Best for Large Greenhouses?

Horticultural glass is a specialized type of glass designed for greenhouse use. It typically offers high light transmission and may have properties that enhance plant growth, such as increased diffusion or specific spectral qualities.

Aesthetics and Design

The visual appeal of your greenhouse can be an important consideration, especially if it’s located in a visible area.

  • Glass greenhouses offer a classic and aesthetically pleasing look. The transparency of glass creates a sense of openness and allows for clear views of the plants inside.
  • Polycarbonate greenhouses can sometimes appear less aesthetically pleasing than glass due to the slightly opaque nature of the material. However, advancements in polycarbonate technology have led to clearer panels with improved aesthetics.

Specific Commercial Greenhouse Crop Needs

The choice between polycarbonate plastic for greenhouse and glass can also depend on the specific crops you’re growing.

  • For crops that require high light intensity and benefit from direct sunlight, large glass greenhouses may be more suitable.
  • For crops that thrive in diffused light or are sensitive to excessive heat, poly greenhouses may be a better option.

Factors to Consider for Crop Selection

The choice between polycarbonate and glass can significantly impact your crop yield and quality. Here’s a breakdown of factors to consider when selecting the best covering material for your specific crops:

1. Light Requirements

  • High-Light Crops: Crops like tomatoes, peppers, and cucumbers thrive in high-light environments. Large Glass greenhouses are often preferred for these crops due to their superior light transmission, allowing maximum sunlight to reach the plants.
  • Low-Light Crops: Some crops, such as lettuce and herbs, can tolerate or even prefer lower light levels. Polycarbonate plastic for greenhouse, with it light diffusion properties, can create a more even distribution of light, preventing leaf scorch and promoting healthy growth.

2. Temperature Sensitivity

  • Warm-Season Crops: Crops like melons and squash require warm temperatures for optimal growth. Polycarbonate greenhouses offer better insulation, helping to maintain warmer temperatures and extend the growing season, especially in cooler climates.
  • Cool-Season Crops: Crops like spinach and kale prefer cooler temperatures. Glass in greenhouse can be more suitable for these crops in hot climates, as they allow for better ventilation and heat dissipation.

3. Growth Habits

  • Vining Crops: For vining crops like tomatoes and cucumbers, consider the height and support requirements. Glass materials with their higher ceilings can accommodate taller vining crops more easily.
  • Compact Crops: For compact crops like lettuce and herbs, space optimization is crucial. Polycarbonate greenhouses can be more flexible in terms of design and layout, allowing for efficient use of space.

4. Other Factors

  • CO2 Requirements: Some crops have higher CO2 requirements for optimal growth. Glass can be more effectively sealed to maintain higher CO2 levels.
  • Pest and Disease Control: Consider the susceptibility of your crops to pests and diseases. Poly greenhouses can offer better protection from pests and diseases due to their tighter seals and reduced air infiltration.
  • Specific Cultivar Needs: Different cultivars within the same crop species may have varying light and temperature requirements. Research the specific needs of your chosen cultivars to make the best material selection.

Examples

  • Leafy Greens: Lettuce, spinach, and kale often benefit from the diffused light and insulation of poly greenhouses.
  • Tomatoes: While tomatoes generally prefer high light, some cultivars may benefit from the diffused light and heat retention of polycarbonate in hot climates.
  • Ornamental Flowers: Light-loving flowers like roses and orchids often thrive in glass greenhouses with maximum light transmission.

Climate Considerations

Your local climate plays a crucial role in material selection. Here’s a deeper dive into how different climates influence your choice between glass and polycarbonate:

Harsh Winters: The Polycarbonate Advantage

In regions with harsh winters, like the northern US and Canada, the superior insulation of polycarbonate greenhouses can be a major advantage. The multi-wall panels with their insulating air pockets help reduce heating costs significantly and maintain stable temperatures even in sub-zero conditions. This is particularly important for commercial growers in states like Alaska, Montana, and North Dakota, where temperatures can plummet to -50°F (-45°C) or lower.

Key Considerations for Cold Climates:

  • Snow Load: Choose polycarbonate panels with a high snow load capacity to withstand heavy snowfall.
  • Wind Resistance: Ensure your greenhouse structure is designed to withstand strong winter winds.
  • Heating Efficiency: Invest in energy-efficient heating systems to minimize operational costs.

Hot Climates: The Glass Greenhouses Challenge

In hot climates, such as those found in the southern US and parts of California, glass greenhouses may be more prone to overheating. The high light transmission of glass can lead to excessive heat buildup inside the greenhouse, potentially stressing plants and increasing cooling costs. However, proper ventilation and shading can help mitigate this issue.

Key Considerations for Hot Climates:

  • Ventilation: Maximize airflow with adequate ventilation systems, such as roof vents and sidewall vents.
  • Shading: Use shade cloth or other shading methods to reduce light intensity during peak hours.
  • Cooling Systems: Consider installing evaporative cooling systems or other cooling measures to maintain optimal temperatures.
Feature Glass Greenhouses Polycarbonate Greenhouses
Light Transmission Excellent (over 90%) Good (80-85%)
Light Diffusion Lower Higher, more even light distribution
Durability Can be prone to breakage, but tempered glass offers high impact resistance (up to 200 psi) Very high impact resistance, virtually unbreakable
Insulation Lower, potentially higher heating costs Excellent, especially multi-wall panels (R-value of 1.54 per inch)
Cost Higher initial investment ($2-$2.50 per square foot) Lower upfront cost ($0.12 per square foot)
Maintenance Lower, longer lifespan (40-50 years) Can require more frequent replacement (10-25 years)
UV Protection Allows some UV transmission, may require shading for some crops Blocks most harmful UV rays
Aesthetics Classic, aesthetically pleasing Can appear less aesthetically pleasing, but newer options offer improved clarity
Weight Heavy, requires stronger framing Lightweight, easier to handle and install
Recommended Thickness 4mm for roof, 5mm for side walls [51] 8mm for sidewalls, 10mm for roof
Other Considerations Can be more prone to overheating in hot climates Can trap moisture between layers, potentially leading to algae growth

Regional Trends and Statistics

Interestingly, regional trends in greenhouse material usage often reflect climate considerations. For example, in Canada, where winters are long and harsh, polycarbonate greenhouses are increasingly popular, especially in provinces like Alberta and Saskatchewan. Conversely, in warmer regions like California, glass greenhouses are still prevalent, particularly for crops that require high light levels. 

Key Climate Factors

When making your decision, consider these key climate factors:

  • Average Temperatures: Evaluate the average temperatures throughout the year, including minimum and maximum extremes.
  • Wind Speeds: Assess the typical wind speeds in your area, especially during storm seasons.
  • Hail Frequency: Determine the likelihood of hailstorms and the potential for damage to your greenhouse covering.
  • Snowfall: If you live in an area with snowfall, consider the average snowfall amount and the weight it can place on your greenhouse structure.

Conclusion

Both glass greenhouses and polycarbonate greenhouses offer unique advantages and disadvantages for commercial growers. The best choice depends on a careful evaluation of your specific needs and priorities, including:

  • Light transmission and diffusion
  • Durability and impact resistance
  • Insulation and heat retention
  • Cost and maintenance
  • UV protection
  • Aesthetics and design
  • Specific crop needs
  • Climate considerations

By carefully considering these factors, you can select the covering material that will optimize your greenhouse environment, promote healthy plant growth, and contribute to the success of your commercial operation.

Further Resources:

Start Saving Time & Money:
Get a Free Demo

Get Started Today
GrowDirector
Open chat
Ask us anything 👋
Scan the code
Chat with GrowDirector
Welcome! 🤝
Chat here for personalized recommendations 🥬🥦