Greenhouses 101


Are You Ready To Buy A Greenhouse?

Majority farmers are buying greenhouses for the first time, and they have many questions about both the use of the greenhouse and the choice of products.First Timers find the process to be somewhat challenging when they see the variety of products offered and when encountering so much detail & so much at once.

The most important step you can take as you prepare to select your greenhouse is to decide what size you’ll need. Once you move in and start growing it won’t be long before your success will overflow the place. Plan to buy the largest greenhouse your space and budget will allow. you can answer the questions below, you are ready to buy a Greenhouse.


Greenhouses on today’s market can be built from a great variety of materials and in several different shapes & styles. After working with our customers and helping them to wade through all the choices and questions that arise, we at the Yard works present the following facts that should help to make an informed decision on the Greenhouse that will best meet you needs for quality, performance and budget!


The clear part of the greenhouse is referred to as glazing. You will find greenhouses using poly film, polycarbonate (Lexan or Macrolon, or polygal.etc.) acrylic, glass or fiberglass. Any material used to glaze the greenhouse should have the highest possible light transmission for optimum plant growth and be resistant to UV damage. The thermal factor of the glazing is also a big consideration when choosing a greenhouse. The chart below is a comparison of the most commonly used materials. Thermal benefit, light diffusion properties, durability, safety etc. are all things that one should consider when choosing a greenhouse.

Glazing Comparison Chart

Glazing Materials


Glass Poly Film Polycarbonate






Breakable YES NO  NO  NO  NO NO
Light Transmission 91% 81 86% 86% 86% 90% (INITIALLY)*
Thermal insulation NONE NONE 40%  R1.40 54%  R1.54 60%  R1.60 NONE
Light Diffusion NO NO YES YES YES YES
  • Fiberglass will support growth of organisms such as algae, and therefore looses light transmission quickly.


Framework of the greenhouse can be made from an assortment of materials such as wood, steel, plastic pipe, aluminum (painted & unpainted).

Wood: Wood frames are easy to construct and wood is a very strong product to use for the greenhouse frame. Among woods, redwood is the best choice since it contains natural resins making it insect resistant. Beautiful when new, Redwood & cedar will gray in color. Some owners like this natural patina. Others prefer to stain or paint the wood with a latex based stain. If neither of these things appeal to you then you may want to consider another frame material.

Aluminum: Aluminum is light weight and will never rust. It is however not as visually appealing to some gardeners who prefer a natural look or a more finished frame. Unpainted aluminum will oxidize over time, but will not support growth of algae or organisms. Painted aluminum is more expensive, but will retain its good appearance virtually forever. The strength and quality of the aluminum is key to the overall strength of the greenhouse frame.

It is easy to bend thin aluminum, so be sure the frame is strong enough to support a snow load on the greenhouse. Some aluminum frames molds have gaskets around each glazing panel. This also a plus on the thermal energy factor, preventing heat & cold collected by the frame from transmitting through the glazing. It’s also a good protection against leaking of rain around the glazing.

PVC Pipe used in greenhouse frame construction is usually bent or curve, and joined together by T and L fitting, much like the plumbing system in you home. It is inexpensive material, but not usually UV treated for long term exposure to the sun. Ask before you buy. This material is not a long term investment, but is usually used for temporary or portable small shelters. Warm weather may cause the pipe to flex a bit (sagging) , and cold temps (freezing) will make it brittle.

Galvanized steel is used mostly in commercial greenhouses or hoop style building. Not real glamorous, but very strong. Over time can rust. Not used often in hobby houses.

Venting Methods

Venting the greenhouse is the job of the builder or designer. If done improperly, trouble with overheating can result. When buying a greenhouse kit, be certain that the venting will do an aequate job of allowing excess heat to escape.If building from scratch, be a bit of a scientist before you start cutting and hammering, making sure that you venting will perform properly.

Hatch style roof vents with low intake . (Can be opened by hand, but are usually fitted with non electric solar vent openers.)Cross ventilation: Exhaust vent placed high in the greenhouse(outbound ) low intake shutters.

A fan takes air out of the greenhouse through an opening in the wall and shutters on the opposite side open th allow air to ve drawn into and through the greenhouse by cnegative air pressure. An electric theermostat is needed to turn the fan and shutters on and to close them, according to the temperature of the air inside. This is used by more growers with warm temperature requirements for the plants such as orchids and tropicals.

Note: Even a properly vented greenhouse may at times need some additional cooling measures. Shade cloth, misting systems and humidifiers can be used to assist in cooling.

Venting Formula: Square footage of the Glazing x .25= vent area. (door may be included).


A fan should be operating inside the greenhouse at all times.Air must move around inside so the plants can get carbon dioxide. This also keeps moisture from sitting on the leave and surfaces and strengthens plants. No matter what venting technique is used in your greenhouse (see above) you must still have fans working inside even when the vents are closed. This will also assist the air in moving out of the greenhouse when the vents are open, helping with the cooling process in warm weather. If the greenhouse has an the automated shutter/fan system you STILL need the interior circulation fan. Several small fans make it easy to distribute air movement, rather than having it very breezy in one area such as a large fan would do. If there is no acess to elcetricty for your greenohosue, be certain you can open and shut the door to allow fresh air movement on a daily basis, or you’ll run the risk of stagnant air and starving plants. Maybe also some organizm growth like mold or algae!

Not every Greenhouse grower will need a lot of complicated devices to have a successful greenhouse operation. If you cover the basices by purchasing a quality structure with adequate ventilation and good thermal properties, the rest can be played by ear and addressed as Mother Nature orchestrates her symphony of Seasons!


Not all greenhouse gardening requires heating. You may be interested in using a heater in the greenhouse, particularily for winter growing. The type and size of the heater depends on these facts: Greenhouse Size, thermal rating of the glazing material, your fueling options, your expected lowest temperature for your region, and the desired heat needed by the plants you intend to grow.

In most areas gas is less costly than electricity, however not always available to everyone.Propane is usually easy to acquire and a rental tank with refill service is a good option for a large greenhouse.

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