Chapter 1

Greenhouse Structures and Design

Greenhouse Site Selection

The greenhouse structure represents both the barrier to direct contact to the external environment and the containment of the internal environment to be controlled. The greenhouse has to protect plants against extreme temperatures, wind, snow, rain, hail, birds, and insects. The efficiency and productivity of a greenhouse operation is largely dependent on the type of growing structure used. Since there are many designs to select from, it is important to become familiar with the advantages and disadvantages of each. The following is a discussion of commercial greenhouses and their structural components.

Microclimate

Climatic conditions have dictated worldwide geographical shift in horticulture. Such forces are also at work within local regions. The primary limiting factor to crop production in greenhouses is low light intensity during the winter. Areas having frequent fog, inclement weather, or shadows cast by trees or tall mountains are poor for crops in general.

Water Availability and Quality

Water is one of the most frequently overlooked resources in the establishment of a greenhouse business. A sufficient quantity of high quality water is extremely important for the production of greenhouse crops. The need for frequent irrigation requires careful planning and management, to ensure that operations have sufficient water to maintain adequate supplies for crop production. Although water is usually obtained from deep wells, generally municipal systems can also supply water of adequate quality for greenhouse production.

Physical Site Requirements

The topography of the site affects where a growing structure is built. (Topography refers to the shape of the land, e.g., hilly, steep, rocky, flat.) The surface of the ground should be level. A 0 to 5 percent slope is recommended. Placing a growing structure on a flat surface is efficient because it facilitates easy adjustments to various mechanical controls in the greenhouse, which is economical. A level surface provides good drainage and reduces the cost of grading the land. Normally, on steep terrains, it is recommended to build several separate greenhouses with axes parallel to contour lines. Provisions must be made for the evacuation of rainfall water, and greenhouses should not be situated in hollow lands.

Room for Expansion

A parcel of land larger than the grower's immediate needs should be acquired. The ultimate size of the range should be predicted. Area should then be added to this predicted figure to accommodate service buildings, storage, access drives, and a parking lot. Additionally, extra space should be allotted to cover unforeseen needs. To meet the environmental codes of some municipalities, it is necessary to use holding ponds for water effluent from the range in order to reduce nutrient release into streams. Doubling the area covered by greenhouses would constitute a bare minimum land requirement.

Availability of Labor

Present and future labor needs should be assessed and should be in accord with the labor supply in the area. Procurement of a labor supply has been a perennial problem in the horticulture industry. While the solution has appeared to rest on locating close to an urban area, this brings on a problem of higher wages. The greenhouse owner must also determine if labor is available to perform both routine and harvest-time duties.

Infrastructures

Proximity to transport networks (e.g. roads, railway), access to communication systems (e.g. telephone, internet) and availability of energy (e.g. gas, electricity) must all be considered. Greenhouses also need convenient access to materials for growing plants (growing media, fertilizers, pesticides, etc.). Transportation requirements to the greenhouse site relate directly to the intended operation's size and marketing arrangements.

Legal Considerations

Site selection involves various legal considerations. Permits, licenses, and zoning regulations govern where a greenhouse may be built and often even dictate what type of building materials may be used. Selecting an appropriate site also involves how the greenhouse operation affects its neighbors. If the proposed site is near a school, hospital, or residential community, the greenhouse must cooperate with the zoning rules of these entities. If water from the site drains into parks, farms, or ecological areas, the land may be subject to various state and federal regulations. Some states require the owner to obtain certification to purchase restricted-use pesticides. In addition, the greenhouse owner must also be aware of relevant mandates from the Occupational Safety and Health Administration that ensure employee safety.

Greenhouse Orientation

Quite possibly the largest design consideration when planning a winter or year-round greenhouse is determining the orientation and angle of glazing for the structure. In general, growers optimizing for winter growing should orient their free-standing greenhouse in an east-west orientation, meaning that the longer, glazed side of the greenhouse should face south, with the shorter ends facing east and west. This orientation allows low angle light from the winter sun to enter from the side where it will not be blocked by ribs of the frame. In the orientation of multi-bay greenhouses structural components come into play.

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