Where You Live
Geographical location is the most pertinent factor to consider when picking out a greenhouse frame. Researching and understanding the environment that you plan to grow in is the first step in the process of picking a frame that will best suit your needs within your location.
If you live in an area that gets annual snowfall, choosing a frame style that has a steep pitch will help snow shed during the winter months and allow for ease of removal after a large storm. Choosing the greenhouse steel tubing outside diameter (OD) is the next important factor to consider. We offer our greenhouse frames with two different options. 1 ⅞ OD steel which is strong enough for environments that get snowfall during the winter or 2 ⅜ OD for areas that get severe winters.
Your sidewall spacing is also a major factor to consider relative to the environment. 4’ spacing will be the strongest option for greenhouses, 5’ is average and the most common option, and 6’ spacing is the weakest and is generally only used in mild environments with minimal weather. Optional V-Truss packages are available on all frame styles and will strengthen the greenhouse as well as keep the greenhouse steel from flexing in windy and snowy conditions, minimizing the stress load on the steel.
What You’re Growing
For larger operations, you will likely want either a Gothic frame as it is the strongest freestanding frame or a Semi-Gable as it has the largest interior volume per square foot equating to the most usable grow space.
For smaller operations a Quonset frame can be a great option, especially when starting out. The Quonset is economical and quick to assemble.
Longevity of the Structure
The Gothic frame is the most structurally integral frame and withstands the strongest wind gusts and largest snow loads. The shape of the structure allows the wind to roll over it while the steep pitch enables snow to slide off before building up and causing strain on the structure.
Cultivator & Harvester Quonset Frame
Also known as a high tunnel greenhouse, the quonset frame type has a lower peak height making it more efficient and economical to heat. The quonset frame types are the least visually intrusive frame type as the peak height starts at only 13 feet. Hortitech offers high tunnels in either a 20' Harvester or a 26' Cultivator. The Harvester is a great greenhouse if you are new to growing indoors as it is economical, has low material use, and is quick to assemble.
Storm Semi-Gable Frame
The semi-gable frame type has taller sidewalls and reaches a higher peak than the quonset frame type. The pitch is steep to allow for better snow shed. The Storm Semi-Gable greenhouse type accommodates advanced lighting systems as it has the largest interior volume per square foot. The peak height and large volume enable the most usable grow space and best ease of access.
Night Hawk Gothic Frame
The gothic frame type can handle the most snow load due to its tall peak height and steep structural shape. This design is also the most aerodynamic and is recommended for areas with moderate to high wind conditions. The steep continuous bend rises sharply to maximize vertical space.
Here at Hortitech we’ve focused on creating the most efficient and resilient greenhouses at the most competitive prices. We use high grade steel so that our models can stand up to high winds, heavy snow, and help all of our clients rest easy knowing their plants are safe. Don’t hesitate to give us a call at (541) 480-9392 or send us a message here if you have any questions.
Read on for more information on greenhouse frames, climate controls, plastics, greenhouse irrigation, and more.
Greenhouse Structure Types
Micro-tunnels are long half-cylinder shaped plastic coverings that are small in size(7). These tunnels are too small for people to work in from the inside, about one meter high and one meter wide. They fit over outdoor crops planted in containers or in the ground and are removed when the plants are ready to grow beyond the height of the tunnel.
Macro-tunnels are larger and taller versions of microtunnels(7). They are 4-5 meters wide and 2-3 meters tall. They are easy to construct like microtunnels but due to the smaller volume do not retain as much heat as greenhouses.
Shade houses are tall (3-5 meter high) mesh covers that protect large areas of commercial crops that are grown in the ground or in hydroponic systems(7). Shade houses help protect plants in dry climates with potentially excessive solar radiation, but allow rainfall to pass through.
Greenhouses are constructed from metal frames and covered with translucent plastic film that provide full enclosure and can be equipped with vents, shades, irrigation systems, and lighting(7). Greenhouses can deliver highly controlled optimal growing conditions for plants and protect them from the environmental hazards or inhospitable conditions outside. Greenhouse crops may be grown in containers, benches, or in soil if there is no foundation(5).
Glasshouses are older and very permanent versions of greenhouses that were conceived in 1824 when Jean Baptiste Joseph Fourier observed the greenhouse effect7. He noticed that the surface of plants were overheating when grown outside but grew well and were protected when grown in old glass buildings. The plants continued to flourish even when they were outside of their natural growing season and would die from excessive cold or heat if cultivated outdoors.
Greenhouse Shapes & Styles
Greenhouses come in a variety of shapes and sizes. Greenhouse shape and orientation are important features that influence crop success and operational efficiency(3). Greenhouses that have a shape that follows the slope of the surrounding area also have reduced heating needs. Asymmetric and pitched roof shapes allow for greenhouses to simulate surrounding geography. Less heating is required for east-west facing greenhouses than for north-south facing ones. Latitude has an effect on how much energy reduction is realized. High latitudes show less effect from orientation than lower latitudes. Light exposure and distribution and also be influenced by latitude and orientation so it is important to research a greenhouse site thoroughly.
Gabled greenhouses have straight walls and a triangular peaked roof(9). They are easy to manage and have a good general space construct and layout. Roofs with multiple triangular gables spanning the length of the roof are called ridge and furrow greenhouses. Sawtooth style roofs are similar but the peaks are angled on one side then straight on the other side. The straight side is built oriented towards the most prevalent wind direction. The flow of air from the wind allows for passive ventilation. A skillion style roof is shaped like one large sawtooth. This allows for passive ventilation and transmits the least amount of light in the morning and evenings. Uneven style greenhouse roofs are like a skillion roof with two unequally slanted sides. Uneven roofs are ideal if a location is at high latitude or on uneven land.
Curved and Peaked-Roofed Greenhouses
Flat Arched greenhouse roofs have straight walls and a shallow length spanning arched roof(9). Flat arched greenhouses require active ventilation but have more stable temperature maintenance than gabled greenhouses. Domed roofs are taller arched roofs that can withstand high winds, they provide highly stable environments but are very costly to build and heat. Tunnels are single aches that provide basic temporary protection.
A hybrid between triangular and curved greenhouse roofs is the gothic style greenhouse. The walls of a gothic greenhouse are slanted and the roof comes to a point. A quonset greenhouse is a shorter and less peaked version of a gothic greenhouse(3). Gothic greenhouses have been found to use less energy than gable and quonset shapes greenhouses. The high peak of the gothic design is also best in climates where snow accumulation is of concern.
Commercial greenhouses may be freestanding or gutter connected or mutispan(5). Free standing greenhouses are single structures. Gutter connected greenhouses are linked at gutter level with a series of trusses.
Gutter connected greenhouses are more cost effective in very large areas over 20,000 square feet, can reduce heating and ventilation costs, and use less land. Gutter connected greenhouses may have difficulties with ventilation and even temperature distribution(9). Freestanding greenhouses are easier for maintaining individualized controlled environments. They can better withstand snow and are better suited for land that isn’t level. Freestanding greenhouses are also able to be shut down for periods when not in use.
Greenhouses are a solution to the many challenges facing conventional outdoor agriculture(7). Success of crops is difficult to predict in the face of the limited amounts of land that is capable of supporting crops, unpredictable weather resulting from climate change, and the growing need for agricultural products. Some plants are difficult to grow or require a highly controlled environment to ensure quality for medical products. Greenhouses offer a variety of designs and features that can meet those needs.
Greenhouses are especially popular for cultivation of cannabis. Cannabis quality and life cycle can be highly controlled in greenhouse environments which increases crop success. The high degree of security and control that is attainable through greenhouse propagation is especially important to the medicinal cannabis industry which is subject to high standards for quality and regulation.
Solar radiation passes through the plastic film covering a greenhouse making heat exchange possible(7), The film protects plants from rain and wind. Greenhouses can be simple small enclosures or large automated industrial facilities. Irrigation, ventilation, and supplemental light through times of short daylight must be provided to the plants.
Greenhouse Framing & Covering
Greenhouses can be framed with a variety of materials like aluminum, steel, PVC/plastic, or a combination of materials(9). Steel is typically the strongest and longest lasting material. Floors may be soil, gravel, concrete, or a combination of materials(5).
Glazing is stretched over the frame and comes in a variety of materials(9). Lighting and temperature inside the greenhouse are dependant on the type of material used. Radiation from the sun passes through the greenhouse covering to transmit heat and light to plants(6). The greenhouse covering, called glazing, greenhouse fabric, plastic, or poly lets short waves of light through and blocks long waves that can be damaging.
Clear coverings do not provide light filtration to the extent that opaque plastics do; the amount of light diffused depends highly on the material used. At all latitudes, east-west oriented greenhouses provide the best year round light exposure. Polyethylene or polycarbonate glazing may discolor over time from UV exposure and eventually will need to be replaced but are typically resistant to potential environmental damage from weather(9). Glazing with higher R-values has better insulation.
General Overview of Glazing
|Glazing Material||R-Value||Light Diffusion||Lifespan|
|Glass||0.95 (single pane)||No diffusion||Impact and scratch resistant, lasts 30 years or more|
|Fiberglass||0.85||Moderate||Resists corrosion and chemicals, warping, thermal expansion, may yellow with UV exposure over several years|
|Polyethylene Film||0.85 (single pane)||Semi-diffused||Inexpensive, easy to replace, good for large greenhouses, needs replacement every few years|
|Polyethylene Sheeting||2.1-2.3||Diffused||Lightweight, stiffer than film and better insulation, UV resistant|
|Polycarbonate||1.43-1.89 (2 ply) 2.0-2.1 (3 ply)||Diffused||Light but durable, light transmission degrades from UV discoloration, lasts 15+ years, difficult to use with curved designs|
Modern greenhouse fabric options are endless and customizable. Soft polyethylene or stiff polycarbonate glazings are commonly used and offer a variety of features such as different types of light filtration and diffusion, and flame resistance. Building codes, climate, and intended crop will play a large role in determining what poly to use.
Ventilation can be naturally provided in a greenhouse through roll up curtains on the sides and roof. Air flow through curtains increases when structures are taller. Exhaust fans, shutters and air circulators can be installed to provide forced ventilation. Shutters are important when fans are used and must be appropriately sized to the fan, open when it is running, and closed when it is off. Shutters and fans can be automated. Scrubbers are a type of ventilation that may be installed to diffuse odors. Ventilation and shades keep spaces from overheating and for regulating humidity and temperature. Ventilation is critical if a heat generating light source is being used due to the fumes.
Greenhouse Heat and Light
If you live in a geographic location that experiences seasons and want to grow year round, heating will be a necessary consideration. Heat pumps and convection tubes are two methods of heating a greenhouse. Propane burning heaters have an added benefit of increasing CO2 in the greenhouse, which stimulates plant growth. Use of night curtains and insulation on the north wall of a greenhouse can reduce heating requirements significantly during the day and night(3). For more on greenhouse heating visit our heating page In the instance of growing cannabis, in general it does not tolerate cold so it is important to maintain a warm environment(10).
Greenhouse lighting can be hung inside to ensure that plants receive consistent levels throughout the year. Lighting may also be utilized to control plant growth cycles and is especially important to control when cultivating cannabis(8). If natural light is too intense, shades and screens can be used to add protection. Blackout shades or shutters ensure that light pollution does not damage crops like cannabis that are very sensitive to the timing of light exposure.
Types of lighting(9)
|Bulb Type||Light Color||Use||Lifespan|
|Metal Halide||Blue, 450-470 nm||Primary Lighting, Leafy Plants||~10,000 hours|
|High Pressure Sodium||Orange-Red, 590-650 nm Full Spectrum Available||Secondary Lighting, Budding and Flowering||~18,000 hours|
|Fluorescent (CFL or T5)||2700k-3000k: High Red 5000k: Full Spectrum 6500k: Blue||Vegetative or Flowering (depending on type), Low Heat||~20,000 hours|
|Incandescent||White Light/Daylight, Some Red||Inefficient, Supplement Lighting||~750-2500 hours|
|LED||Customizable||Primary Lighting, High Efficiency, Low Heat, Dimmable||~50,000 hours|
More on Growing Cannabis
Cannabis is a short day plant that thrives in ample light and will begin flowering when exposed to a threshold level of red light(2). Naturally this is a cue that days are shortening and dusk is coming sooner, which tells the plant it is time to flower(1). 70 watts per meter PAR (photosynthetically active radiation) minimum should be maintained 18-24 hours a day to keep cannabis plants in a vegetative state(2). Dropping light exposure to 12 hours of light and 12 hours of dark will trigger budding so lighting control is vital to successful greenhouse cultivation of cannabis.
Humidity and Temperature
Wet walls and misters are used to keep the environment in the greenhouse humid(7). Humidity helps plants cool themselves, not unlike sweating for humans(8). For growing cannabis, 75% relative humidity in the juvenile stage and 55-60% during active vegetative and floral growth is ideal(2). 25-30°C is the ideal temperature for growth. Humidity is relevant to temperature, so humidity recommendations generally assume the temperature will be around 25°C. Even slight increases in temperature such as 28°C can increase potential for pests and pathogens8. While cannabis thrives at temperatures up to 35°C, such high temperatures are hazardous for workers and encourage pest and pathogen growth(2).
Water and Irrigation
Water based hydroponic growing systems may be utilized in greenhouses(7). Drip irrigation is a common method of water delivery. Flood tables or floodable floors are also commonly used(5).
Types of Irrigation(9)
|Drip Tape||Delivers water in small amounts directly to roots via flat polyethylene hose with perforations||Convenient for stationary plants and delivering fertilizer|
|Drippers||Similar to drip tape but tape is buried, direct delivery of water to roots||Convenient for stationary plants and delivering fertilizer|
|Sprayers and Misters||Hoses connect to nozzles that produce a fine mist of water over plants, produces significant waste water||Useful for multiple zoned greenhouses and semi-automation|
|Manual Watering||Water delivered by hand through hoses or watering cans, labor intensive||Allows for direct oversight|
|Capillary Mats||Mats that fill with water, water is pulled up into the soil to the roots||Low waste and avoids overwatering|
|Hydroponic Systems||Plants are grown in non-soil medium that secure the plant in place in a container circulated with water and nutrient solution||No additional irrigation needed|
Carbon Dioxide in Greenhouses
Injectors or combustion heaters can be used to increase CO2 levels inside the greenhouse(7). Many plants respond very well to elevated CO2 environments and produce higher yields(4). Cannabis especially responds well to CO2 enrichment. ~750 ppm carbon dioxide, double the normal concentration, can increase photosynthesis rates in cannabis by 38-48%(2).
Automatic controls and computerization allow limits to be set for conditions and the necessary controls to activate or deactivate when limits are reached(7). These systems can collect usage data that can be analyzed to optimize environmental control systems and optimize yields and efficiency. Greenhouses with partially or fully automated controls are expensive but provide many benefits.
Benefits of Automated Greenhouses(7)
- Production quality is ensured to high standards when technology is properly utilized.
- Crop yields are greatly increased, especially in hydroponic automated greenhouses, and crops are able to be grown on land that otherwise would not sustain agriculture. Social concerns of land and food scarcity can be mitigated by high yield indoor cultivation.
- Quality standards are more easily maintained and deviations can be traced allowing for easier regulatory compliance.
- Production calendars can be controlled and manipulated regardless of season in automated environments.
- Automated controls are optimized to reduce waste and energy use and reduce operating costs.
- Low-skilled labor at this time is more scarce than skilled-labor so having fewer skilled laborers may make more sense than having several low-skilled laborers working traditional outdoor fields.
Choosing a reputable greenhouse supplier with experience and knowledge will ensure your greenhouse is built right. Growers should look for companies that offer good customer service and can guide them long term if challenges arise. Greenhouses can be utilized for a large variety of crops, so if a grower is cultivating a particular plant it is wise to look for a greenhouse supplier with experience with that crop. This is especially important for plants like cannabis that are very dependant on proper environmental conditions.
Growers looking to build a greenhouse should carefully consider and research the following factors:
- Site Selection
- Engineered Plans
- Climate Controls
- Environmental Control
- Water Management and Irrigation
- Nutrient Management
- Pesticide Use
- Insect, Mite, and Disease Management
- Waste Management
- Energy Conservation
- Building Code and Local Ordinances
For further guidance The National Greenhouse Manufacturers Association (https://www.ngma.com/) can be contacted for specific building standards(9).
- Chamovitz, D. 2012. What a plant sees. In What a plant knows (9-26). Ne7w York, NY: Scientific American/Farrar, Straus and Giroux.
- Chandra, S., Lata, H., ElSohly, M.A., Walker, L.A., & Potter, D. (2017). Cannabis cultivation: Methodological issues for obtaining medical-grade product. Epilepsy & Behavior, 70, 302-312. DOI: 10.1016/j.yebeh.2016.11.029. Retrieved from http://www.epilepsybehavior.com/article/S1525-5050(16)30588-1/abstract
- Gupta, M. J., & Chandra, P. (2002). Effect of greenhouse design parameters on conservation of energy for greenhouse environmental control. Energy, 27(8), 777-794. Retrieved from https://www.sciencedirect.com/science/article/pii/S0360544202000300
- Kimball, B.A. (1983). Carbon dioxide and agricultural yield: An assemblage and analysis of 430 prior observations 1. Agronomy Journal, 75(5), 779-788. DOI: 10.2134/agronj1983.00021962007500050014x. Retrieved from https://pubag.nal.usda.gov/pubag/downloadPDF.xhtml?id=53689&content=PDF
- Lopes, P, and Smith, T (Eds.). (2010). Massachusetts greenhouse Industry best management practices guide. Amherst, MA: UMass Extension and Massachusetts Department of Natural Resources. Retrieved from https://ag.umass.edu/sites/ag.umass.edu/files/book/pdf/greenhousebmpfb.pdf
- Odesola, I.F., & Ezekwem, C. (2012). The effect of shape and orientation on a greenhouse: a review. AFRREV STECH: An International Journal of Science and Technology, 1(1), 122-130. Retrieved from https://www.ajol.info/index.php/stech/article/view/108059
- Ponce, P., Molina, A., Cepeda, P., Lugo, E., & MacCleery, B. (2014). Chapter 1: Introduction. In Greenhouse design and control (1-28). Leiden, Netherlands: CRC Press. Retrieved from https://books.google.com/books?hl=en&lr=&id=IuisBAAAQBAJ&oi=fnd&pg=PP1&dq=greenhouse+design+and+control&ots=WnnqS9j2sn&sig=azOkuIlqVWjP-sXhPSGqvPSsRKg#v=onepage&q=greenhouse%20design%20and%20control&f=false
- Potter, D.J. Chapter 4: Horticulture. (2016) In Pertwee, G (ed.) Handbook of Cannabis. Oxfored, UK: Oxford University Press, 65-88. Retrieve from https://books.google.com/books?id=hPVwBAAAQBAJ&lpg=PP1&dq=cannabis&pg=PR13#v=onepage&q=cannabis&f=false
- Research and Commercial Greenhouses Information. (n.d.). Engineering 360, IEEE Global Spec. Retrieved from https://www.globalspec.com/learnmore/building_construction_under_construction/building_systems/commercial_research_greenhouses Small, E. (2017). Cannabis: a complete guide. Boca Raton, FL: CRC Press. Retrieved from [https://books.google.com/books?id=oo2KDQAAQBAJ&printsec=frontcover&dq=cannabis&hl=en&sa=X&ved=0ahUKEwibjLSNsdXZAhXm7YMKHYHPCgkQ6AEILjAB#v=onepage&q=soil&f=false