Types of Greenhouses: Pros & Cons

When most people think of a greenhouse, they think of an enclosed structure that raises the temperature inside for plant growth. And greenhouses do provide the home gardener and commercial grower the opportunity to alter their climate zone and increase the growing season throughout the year. But they also do much more. There are three basic categories of greenhouses that provide the gardener with different environments to extend their growing season or alter their climate zone:

The Hot House: Hot greenhouses are for plants or trees from tropical climates, or exotics such as mangoes or orchids. The hot greenhouse keeps a temperature above 65 degrees Fahrenheit and maintains a moist, humid environment in which plants may grow and prosper. Depending on your climate zone, this may require adding grow lights or an additional heating system.

The Warm House: Warm greenhouses are kept at 50 to 55 degrees Fahrenheit and are an acceptable environment for flowers, fruits and vegetables that are usually grown in warmer months. The most conspicuous benefit of the warm greenhouse is its ability to extend your growing season into the fall and winter months and to get a head start on the spring planting season. In colder latitudes, this may also require grow lights or an additional heating system.

The Cool House: Cool greenhouses are set up to maintain interior temperatures of 40 to 45 degrees Fahrenheit. These are used for starting your plants from seeds or hardening off seedlings before moving them to larger containers or into planting beds. The cool greenhouse is particularly useful for cool weather crops, such as beets, chard, leafy greens, peas and winter vegetables.

Cool House

Warm House

Shapes and Structures

Your greenhouse can share an existing wall of your house or garage. By attaching the greenhouse to an exterior wall of your house, you need only build three additional walls and the roof to complete the greenhouse. Look for an east- or west-facing wall to keep your greenhouse's longest side and roof facing south, where it can receive maximum sunlight. A freestanding (detached) greenhouse is an independent structure in your garden. This may provide you with more options on where to place the greenhouse.
Either attached or detached structures can have a concrete or brick foundation. Some greenhouses that are supplied with an integral frame can be anchored directly to the ground.

• The lean-to is usually found in home or hobby gardens. Because of the limited interior space, they are seldom used for commercial enterprises.
• The Quonset is the most common structure found in commercial enterprises. They are built from curved or arched rafters and feature solid walls for support.
• Gable greenhouses lend themselves to heavy-duty coverings, such as glass and fiberglass. Curved arch greenhouses tend to be covered with lighter materials such as polyethylene or polycarbonate based materials.
• Gutter-connected greenhouses are found in a variety of shapes and construction technique. Arch, gothic arch, cable-connected or gutter-connected, models are available in 12-foot increments, with or without roof vents.

Lean-to Greenhouse

Gable Greenhouse

Whatever the shape, greenhouses can be constructed from a variety of materials. Frames can be aluminum, PVC, steel or wood. Your choice will depend on a number of factors. How important is the look of your greenhouse? What is your budget? How much time do you want to spend on maintenance?

Covers

Glass is the most traditional covering for greenhouses. It can be used for slanted sides, straight sides, roofs and eaves. Aluminum-framed greenhouses with glass covers provide a low-maintenance solution and a weather-tight structure. The only downside is that glass easily breaks and is costlier than plastic alternatives.
Fiberglass greenhouses are light, strong and hail-resistant. Be aware that lower-quality fiberglass will discolor over time and reduce the penetration of sunlight. Look for high-quality fiberglass and avoid colored versions.
Plastic greenhouses are gaining in popularity. They offer a low-cost alternative to glass, absorb sufficient heat and produce the same quality fruits and vegetables as glass does.
Polyethylene is lightweight and inexpensive. It performs well during fall, winter and spring, but tends to deteriorate during the summer when it gets more extreme exposure to the sun. Ultraviolet rays are the culprit. Deterioration begins first along the rafters and along the creases. There is also UV-inhibited polyethylene, which is available in 2- and 6-mL thickness but it is more expensive.

Plastic Cover 

Glass Cover

Frames

The greenhouse frame can be made of aluminum, PVC, galvanized steel or wood. Each has its own advantages and disadvantages.

Timber Frames
Advantages

• Traditional material
• Attractive appearance
• Hardwoods such as cedar retain their color well, do not warp easily and are rot-resistant

Disadvantages

• Expensive
• Heavier during constructing
• Timber, other than hardwoods, must be pressure-treated with preservative and painted regularly to prevent dry rot

Aluminum Alloy Frames
Advantages

• Maintenance-free metal alloy
• Requires narrower frames than wood-framed greenhouses, allowing for larger panes of glass and better light penetration

Disadvantages

• May be considered less attractive than wood-framed greenhouses
• Slightly reduced retention of heat when compared to wood frames

Aluminum Alloy Greenhouse

Galvanized Steel Greenhouse

Galvanized Steel Frames
Advantages

• Light and easy to build
• Very strong and ridged material
• Cheaper than timber or aluminum frames
• Narrower frames than wood-framed greenhouses, allowing for larger panes of glass and better light penetration

Disadvantages

• May be considered less attractive than wood-framed greenhouses
• Slightly reduced retention of heat compared with wood frames
• Must be painted regularly to prevent rust

Greenhouse Glazing

Horticultural Glass
Advantages

• Lighter and less expensive than window glass
• Excellent light penetration
• Improved heat retention
• Easy to clean
• Will not discolor

Disadvantages

• More fragile than plastic
• Cracked or broken panes must be replaced immediately to prevent heat loss

Plastic Pane

Glass Pane

Plastic Panes
Advantages

• Less expensive than glass
• Easy to shape for curved structures

Disadvantages

• Shorter lifespan than glass
• Easy to scratch
• Discolors over time, reducing the amount of light in greenhouse
• Condensation forms on its surface far more readily than on glass

Rigid Polycarbonate Panes
Advantages

• Less expensive than glass
• Easy to cut from sheets with simple tools
• Good insulating material

Disadvantages

• Shorter lifespan than glass
• Easy to scratch
• More opaque than glass or other plastics, reducing the amount of light in the greenhouse

Your greenhouse's performance and your satisfaction will depend largely on the type of materials you decide to use. Ridge and furrow greenhouses offer the greatest use of space in gardening and crop production. Aluminum is the most durable and is commonly used as framing material for commercial greenhouse structures. Glazing will always be a tradeoff: expense vs. lifespan. Understanding your needs, such as space, budget and environment, will be the foundation to your satisfaction with whatever greenhouse you choose.