Selecting a proper site for your greenhouse is just as important as selecting your construction materials, seeds, plant nutrients, and countless other components needed to ensure success. As many aspects should be considered when choosing a site, what follows are 12 factors to take into account before you make this important decision.
These site selection tips are from a presentation made by Pat Rorabaugh, a professor in the School of Plant Sciences/Controlled Environment Agriculture Center (CEAC) at the University of Arizona, at the Greenhouse Crop Production & Engineering Design Short Course that was held in Arizona in April.
1 Solar radiation: Since plants require light for photosynthesis, it’s critical to determine how the sunlight will reach them. Low light reduces photosynthesis and causes slow growth and fruit and flower abortion. The result is a low yield and minimal financial return. The location of your greenhouse and the time of year make a big difference in photosynthesis; locations that don’t receive enough solar radiation in the winter will need supplemental lighting.
2 Water: About 1 gallon of water mixed with nutrients is needed daily to supply each plant in addition to the water needed for evaporative cooling, which is about 10,000 to 15,000 gallons an acre each day. You can recycle nutrient water to increase your water use efficiency, but be wary of salt build-up. An initial water analysis should be done to assess salt and pH levels. pH levels should be adjusted to around 5.8 to 6.5 for tomatoes and if the source water is basic, as in more than 7 parts per million, add acids such as nitric, phosphoric, and sulfuric. If the source water is acidic, as in less than 7, add a base.
3 Elevation: Elevation affects high summer and low winter temperatures and will affect your cooling and heating costs, as well. For example, tomatoes function best between temperatures of 59°F to 86°F. If you happen to be at a higher altitude, here are several tips on how to control the temperature:
● Place plastic jugs of water around the plants when it’s cold. The water will garner heat during the day, and hold it during the night when the temperature drops.
● Place a temperature alarm in the greenhouse during colder months to alert you when the temperature drops. If necessary, you can place a ceramic heater in the house to increase temperature.
● If you have a rigid structure, use an automatic vent opener to control the heat, and if you have a soft structure greenhouse, you can open a flap to
permit heat reduction.
● During the summer use an automatic water system, possibly one that includes misters. During the winter disconnect all hoses to prevent pipes freezing up and water instead by hand.
4 Microclimate: There are many different factors that can affect your environment including latitude. Sea level at the poles will always be colder than sea level at the equator, and large bodies of water will heat up and cool down much slower than land masses. For example, San Diego, which is next to the Pacific Ocean, has much smaller fluctuations between day and night temperature than does the Sonoran desert, which is not close to a large body of water and whose temperatures can fluctuate.
Take trees, mountains, and other obstructions that could possibly cast a shadow on the greenhouse into consideration, especially in the morning. Mountains also have the ability to affect wind and storm patterns. Other environmental considerations include: clouds and fog, which can gather at certain times of the day in specific areas and reduce sunlight and photosynthesis; high wind that can cause structural damage and suck heat away from the greenhouse; blowing dust and sand which can braze the greenhouse glazing; and lastly, snow.
5 Pest pressure: Make sure to either choose a site that is far away from other agricultural production areas, or create a buffer zone between your operation and other production areas to prevent pest infestation.
6 Level and stable ground: Be aware of the stability of the ground on which you construct your greenhouse; it should not be subject to shifting. The ground must also be graded for water draining (a 6 inch drop in 100 feet). Additionally, the ground must be compacted so that it won’t begin to settle after the greenhouse is built.
7 Utilities: Make sure that you have the following utilities at your disposal:
● Telephone service
● Three-phase electricity
● Fuel for heating/CO2 generation: natural gas, propane, fuel oil, electricity. Alternatives include solar, compost, woodchips, nut hulls, etc.
8 Roads: Access to good roads is a must. For example, if roads are unpaved, when you transport your harvest, the fruit will be subject to all of the rocky movement of the vehicle which could lead to bruising, crushing, and other major damages for your fruit.
9 North-South orientation: The greenhouse as well as the plants inside the greenhouse should be oriented north-south, especially in southern latitudes to maximize the amount of light that enters, and to create the best ventilation possible.
10 Capability of expansion: It’s advisable to purchase more land than you initially need so that you have the possibility of expanding later.
11 Availability of labor: The owner or manager of the operation will need two different types of labor forces:
● Trainable laborers as a retainable workforce. These laborers will take care of the plant and fruit harvesting and packing.
● Specialty laborers. This includes growers, plant production managers, plant nutrition specialists, plant protection specialists, office/computer specialists, labor/management specialists, and marketing specialists.
12 Management Residence: Growers and managers should all live relatively close to the greenhouse in the event of an emergency.
Go to the next page for information on how to get data for potential site locations.
To get information on the location you plan to construct your greenhouse, look into a “community profile.” These profiles can include information on elevation, weather, growth indicators, transportation, utilities, property tax information, labor force info, etc. The information is usually available at the local chamber of commerce or online.