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Greenhouse Materials

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This is part 2 of 4 in the series Greenhouses in Alberta

When setting up a greenhouse in Alberta’s Zone 3, choosing the right materials is important for both your budget and the success of your plants. This post explores the pros and cons of common framing and covering materials, then dives into why hoop houses are a top choice for low-cost setups. Finally, we’ll look at insulation and ventilation—two vital factors for keeping your greenhouse functional in harsh climates.


Framing Materials

an image of a greenhouse and garden by owlcreek.caWood

Wooden frames are a traditional choice among greenhouse enthusiasts, and for good reason:

  • Pros
    • Insulative: Wood provides some natural insulation, helping to retain heat in cooler temperatures.
    • Readily Available: Lumber is easy to find at local hardware stores, often with a range of price points.
    • Aesthetic Appeal: Many gardeners appreciate the rustic or classic look of a wooden greenhouse.
  • Cons
    • Maintenance: Wood must be treated or sealed to prevent rot or insect damage. Over time, you may need to repaint or re-stain.
    • Susceptible to Rot: If it’s not properly treated or if your greenhouse is in a damp area, the wood frame can degrade.
    • Heavier Build: While not as heavy as some metals, wood is still bulkier than PVC and requires a sturdy foundation.

Tips:

  • Choose rot-resistant species like cedar or pressure-treated lumber if possible.
  • Inspect your wood frame each season for any signs of warping or rot, and re-seal as needed.

Metal (Aluminum/Steel)

Metal frames—most commonly aluminum or galvanized steel materials—are a durable option:

  • Pros
    • Durable: Both aluminum and steel can withstand significant wind, snow, and temperature swings.
    • Lightweight (Aluminum): Aluminum frames are lighter and easier to handle than steel.
    • Low Maintenance: Metal frames generally won’t rot or require painting, making them a set-it-and-forget-it choice.
  • Cons
    • Higher Cost: Quality metal framing can be more expensive than wood or PVC.
    • Less Insulative: Metal conducts heat away more quickly, so you may need additional insulation strategies in Zone 3.
    • Potential Corrosion: Although often galvanized or coated, steel can rust if coatings are damaged.

Tips:

  • If opting for a metal frame, consider adding foam or rubber washers where metal contacts polycarbonate or glass to reduce heat loss.
  • Check the frame occasionally for loose bolts or any signs of rust, especially around joints.

an image of a greenhouse and garden by owlcreek.caPVC

PVC frames are popular materials for hobby greenhouses or temporary structures:

  • Pros
    • Lightweight: Easy to transport and assemble, making PVC ideal for smaller DIY or seasonal greenhouses.
    • Cost-Effective: Lower initial investment compared to most wood or metal frames.
    • Flexible: Great for hoop-shaped designs, which naturally shed snow and rain.
  • Cons
    • Less Sturdy: PVC can bend or buckle under heavy snow loads or strong winds if not reinforced.
    • UV Degradation: Over time, UV radiation can make PVC brittle, leading to cracks or breaks.
    • Temperature Sensitivity: Extreme cold can make PVC more prone to cracking, so check regularly.

Tips:

  • Use UV-resistant PVC or paint your PVC frame to extend its lifespan.
  • Reinforce hoops with cross-supports if you expect heavy snow.

Covering Materials

an image of a greenhouse and garden by owlcreek.caPolycarbonate or Acrylic Panels/Sheets

Rigid plastic panels are becoming increasingly popular:

  • Pros
    • Lightweight: Much easier to install and handle compared to glass.
    • Better Insulation: Multi-layer polycarbonate can trap air, helping keep temperatures stable in cold climates.
    • Increased impact-resistance, compared to glass: More resistant to hail or falling branches than glass.
  • Cons
    • More Expensive than Plastic Film: Though cheaper than high-quality glass, polycarbonate panels are pricier than polyethylene film.
    • Condensation: If not properly sealed or vented, moisture can build up in the channels, reducing light transmission over time.
    • Often brittle: Can allow hail to puncture right through, creating holes and causing cracks.

Tips:

  • Opt for double- or triple-walled polycarbonate for improved insulation.
  • Clean panels yearly to prevent algae or dust buildup in channels.
  • Look for hail/puncture resistant sheets.

Plastic Film (Polyethylene)

For gardeners on a budget, plastic film is often the first choice, but it’s beneficial in more ways than affordability:

  • Pros
    • Most Affordable: Easy on the wallet, making it perfect for hobbyists or trial greenhouses.
    • Easy to Install: Can be stretched over PVC hoops or wooden frames with clips or staples.
    • Versatile: Comes in various thicknesses and grades, including UV-stabilized film.
    • Can be puncture resistant: 10-14mm plastic can often withstand large hail and damage from whipper snippers.
  • Cons
    • Often limited durability: Thinner plastic is prone to tearing or punctures; high winds or animal interference can shorten its lifespan.
    • Frequent Replacement: May need to be replaced every few seasons, especially in harsh climates.
    • Heat Retention: Provides some insulation, but not nearly as effective as multi-wall polycarbonate.

Tips:

  • Use UV-treated greenhouse plastic to extend its lifespan.
  • Patch small tears promptly with greenhouse repair tape.

Glass

Glass is a timeless greenhouse material covering, known for its crystal-clear appearance:

  • Pros
    • Excellent Light Transmission: Glass allows the full spectrum of sunlight to enter, which is ideal for plant growth.
    • Longevity: Quality tempered glass can last for decades if properly maintained.
  • Cons
    • Heavy: A stronger (and often more expensive) frame is needed to support the weight.
    • Costly: Glass can be pricier upfront than other coverings.
    • Fragile: In regions with hail or heavy snow, glass can crack or break if not reinforced or if the structure is neglected.

Tips:

  • Consider safety or tempered glass to reduce the risk of shattering.
  • Check roof panels for cracks, especially after storms.

an image of a greenhouse and garden by owlcreek.caHoop Houses: Affordable, simple materials

A hoop house typically consists of a series of PVC or metal hoops covered with a plastic film. The materials and these structures are prized for their simplicity, affordability, and flexibility.

Designing a Hoop House for Zone 3

  • Frame Strength: Consider using metal conduit or thick-walled PVC for increased durability.
  • Anchoring: Securely anchor the hoops to the ground to resist strong winter winds.
  • Extra Supports: Install ridge poles or cross braces along the top to handle snow loads.

Reinforcement Ideas

  • Support Braces: Additional wooden or metal brackets can help distribute weight evenly.
  • Double-Layer Plastic: Some gardeners inflate a gap between two layers of plastic, adding insulation and reducing heat loss.

Pros and Cons

  • Pros
    • Low Cost: Generally more budget-friendly than rigid-panel or glass greenhouses.
    • Versatile: Easy to expand or reduce in size; suitable for seasonal use.
    • Quick Setup: Many hoop houses can be built in a weekend with basic tools.
  • Cons
    • Less Weather-Resistant: Strong winds or heavy snowfall can damage a poorly built hoop house.
    • Shorter Lifespan: Plastic film may require frequent replacement, and PVC frames can degrade in UV light.

an image of a greenhouse and garden by owlcreek.caInsulation and Ventilation

In Alberta’s Zone 3, winter temperatures can remain brutally cold for extended periods. While greenhouses can be heated and insulated to allow for some cold-weather cultivation, they are most efficiently used for extending the growing season into early spring and late fall, rather than attempting to grow through the entire winter. The cost of heating a greenhouse during the coldest months can be prohibitive, and many gardeners find it more practical to focus on maximizing shoulder-season production.

Why Insulation and Ventilation Matter

  1. Temperature Regulation
    • Extended Growing Window: Insulation keeps the greenhouse warmer in the spring and fall, allowing you to start plants earlier and continue harvesting later.
    • Prevent Overheating: Even in cool climates, sunny days can quickly raise greenhouse temperatures to plant-damaging levels. Proper ventilation releases excess heat.
  2. Protecting Plants
    • Frost Protection: Insulated walls and roof coverings help retain heat, reducing the chance of frost damage during cold nights.
    • Reducing Disease: Good ventilation keeps humidity in check, minimizing fungal and bacterial problems.
  3. Energy Efficiency
    • Lower Heating Costs: If you do choose to heat your greenhouse during cooler weeks, insulation prevents heat from escaping too quickly.
    • Sustainable Gardening: By balancing insulation with natural ventilation, you reduce energy consumption and maintain a more eco-friendly setup.

Insulation Solutions and Techniques

  • Horticultural Bubble Wrap: Applying bubble wrap inside the greenhouse can significantly reduce heat loss through windows or panels, especially at night.
  • Row Covers Within the Greenhouse: Covering individual crops or rows with lightweight fabric creates a second layer of protection—essentially a “greenhouse within a greenhouse.”
  • Straw Bales: Placing straw bales along the greenhouse’s perimeter acts as natural insulation, blocking drafts and helping to stabilize internal temperatures.

Ventilation Techniques and Tools

  • Roof Vents and Louvered Side Vents: Manually operated or automatic vents at the roof and along the sides let out hot air and bring in cooler air.
  • Fans: Circulation fans help move air evenly throughout the greenhouse, preventing hot or cold pockets and reducing excess humidity.
  • Roll-Up Sides (for Hoop Houses): Simply rolling up the plastic sides on warm days allows cross-breezes to cool the interior.
  • Thermostatically Controlled Systems: More advanced greenhouses use thermostats and sensors to open vents or run fans automatically, maintaining stable temperatures without constant monitoring.

By combining these insulation strategies with proper ventilation, you can extend your growing season well beyond the usual limits of Alberta’s Zone 3. While fully heating a greenhouse throughout winter may not be cost-effective for everyone, focusing on spring and fall production can be a game-changer for gardeners looking to enjoy fresher, home-grown produce for more of the year.


Key Takeaways for Greenhouse Materials

  • Choose the Right Frame: Wood, metal, and PVC each have strengths and weaknesses. Consider durability, cost, and how much maintenance you’re willing to do.
  • Cover Wisely: Glass, polycarbonate, and plastic film offer different balances between cost, insulation, and longevity.
  • Go Hoop (If You’re on a Budget): Hoop houses provide an excellent option for zone 3 gardeners looking for a quick, low-cost solution, but keep an eye on reinforcement and lifespan.
  • Insulate and Vent: Good insulation retains heat during frosty nights, while effective ventilation prevents overheating and promotes healthy plant growth.

With a well-chosen combination of framing and covering materials—and a smart approach to insulation and ventilation—you can create a greenhouse that stands up to Alberta’s tough winters without breaking the bank. In the next part of this series, we’ll explore how to set up your greenhouse beds, from in-ground planting to raised beds and containers, and discuss the benefits each approach offers in a cold-climate greenhouse.

Amy
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