Greenhouses: Structures Designed for Plant Growth

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Norman Howard
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Greenhouses: Structures Designed for Plant Growth Audience and Scope This document is intended for use in an introductory horticulture course or for individuals looking to gain a better understanding

1 Greenhouses: Structures Designed for Plant Growth Audience and Scope This document is intended for use in an introductory horticulture course or for individuals looking to gain a better understanding of greenhouses. It could be used in a textbook or as a resource for a company who builds greenhouses to give to potential clients. Very little prior knowledge about greenhouses was assumed when writing this document. The purpose of this document is to provide the reader with an understanding of what a greenhouse is and the different components. It also describes the main types of greenhouses that are used. Through reading this document the reader will learn the basic structure of greenhouses and general knowledge about greenhouses. Also, this is not an instructional guide to building a greenhouse.

Introduction Early Egyptian and Roman civilizations used greenhouse structures during the winter months to help protect tender fruits and vegetables.

2 Introduction Early Egyptian and Roman civilizations used greenhouse structures during the winter months to help protect tender fruits and vegetables. Today greenhouses are used to not only for food crops but also for ornamental plant production, crop research and general plant production by horticulturists. A greenhouse is a structure covered with transparent material and designed to provide plants with the proper conditions to grow. Greenhouses are made up of many different components and there are also a variety of types and styles. Components of a greenhouse There are many pieces that come together to build a greenhouse. First there is the base and flooring. Depending on the use of the greenhouse and budget of the builder, the base could simply be bare ground or gravel. However, more expensive greenhouses have concrete floors, which contain a heating source to help regulate the temperature with the structure. The base can also depend on the size of the greenhouse, as very large structures require a more stable base such as concrete while small greenhouses do not. Moving up from the base, the next pieces are the sidewalls. The sidewalls are attached to the base and are what support the roof of the structure. For this reason the sidewalls must be strong yet not create too much shade with large support beams. This is not as much a problem today with the use of aluminum and other strong but light weight metals. Trusses run between the two sidewalls to connect them and support the roof. Again the trusses and roof must create as little shade as possible. Running the length of the greenhouse, connecting all the trusses, is the ridge. This is the highest point of the greenhouse and helps provide support for the roof. These four components, the base, sidewalls, trusses, and ridge, are the main pieces that create the basic structure of the greenhouse. There also other parts of a greenhouse, which help regulate the conditions within the structure. The four basic structural components of a greenhouse are shown in Figure 1 below. D C A Figure 1. Shows the basic structure of a greenhouse. A: ase : Sidewalls C: Truss D: Ridge The conditions in the greenhouse are critical for optimal plant growth. To control the environment in the greenhouse, several mechanisms are used. For temperature regulation, greenhouses use heaters, cooling fans and ventilators. Various heaters are used to help keep the structure warm during the winter. To help cool the greenhouse

3 cooling fans located on the sidewalls draw in air from outside the structure, while ventilators along the roof allow warm air to escape. Heaters, fans, and ventilators keep the structure at the optimal temperature for the plants. Greenhouses are begun to become more sophisticated and include mechanisms to control moisture, carbon dioxide levels and the amount of sunlight. These mechanisms are used mainly in very large commercial greenhouses and are not necessary for basic greenhouse function. Greenhouse Covering One of the most crucial components of a greenhouse is the covering. The covering on the structure is what allows the conditions in the greenhouse to be controlled and changed. There are many different types of covering materials but they must be transparent to allow sunlight to penetrate the greenhouse. The first type of covering is glass, which is one of the oldest kinds of greenhouse covers. Glass provides the best light transmission of any covering material and also UV light does not reduce light transmission through glass over time as it does with other materials. However, glass is expensive to build with and is easily cracked or broken. A newer type of greenhouse cover is plastic film. Plastic film coverings are lightweight and can be easily adapted to a wide variety of greenhouse designs. Plastic film is becoming more popular because it is inexpensive however; it does not last as long. It needs to be replaced every three year because UV light over time reduces the amount of light that passes through the film. Fiberglass-reinforced plastic coverings are semi-rigid with similar transmission rates as glass. The fiberglass creates a more uniform transmission of light as well. Fiberglass-reinforced plastic has become less popular in recent years because it is very susceptible to Figure 2. These are several of the many styles of greenhouses. degradation and it is also flammable. Replacing fiberglass-reinforced plastic coverings in popularity are acrylic and polycarbonate coverings. These are rigid plastic materials and resemble glass panels. Acrylic can be used up to 25 years while polycarbonate can be used between years. They are both very lightweight yet very strong and can be easily installed. The only drawback to acrylic and polycarbonate is that they are flammable like fiberglassreinforced plastic coverings. The material used to cover a greenhouse is very important to its proper function. Each of the covering materials has advantages and disadvantages to its use.

Types of Greenhouses There are three basic types of greenhouses attached, detached, and connected.

Attached greenhouses are connected to a building that is not another greenhouse. In Figure 3A a greenhouse is attached to a school building.

A small attached greenhouse can be mounted in a window of a home, which is very convenient for growing a few plants.

4 Types of Greenhouses There are three basic types of greenhouses attached, detached, and connected. Within each of these types there are different styles even span, uneven span, lean-to, Quonset, Gothic arch and others which are shown in Figure 2. Attached greenhouses are connected to a building that is not another greenhouse. In Figure 3A a greenhouse is attached to a school building. Homeowners often use this type because they are inexpensive to build as they rely on the existing building for support. A small attached greenhouse can be mounted in a window of a home, which is very convenient for growing a few plants. Detached greenhouses, also known as freestanding, are separate from other buildings. The most common style of detached is the even span as seen in Figure 3C. Detached greenhouses are popular because the environmental conditions within the structure are more easily controlled and regulated. Connected greenhouses are actually several greenhouses joined together, shown in Figure 3. They are often used in large commercial settings because the overall cost is less than building several detached greenhouses. It costs less because they require less land and less energy to maintain the environmental conditions within them. A Figure 3. A. Attached. Connected. C. Detached C Conclusion Greenhouses are structures that come in a variety of sizes, types, and styles but all are built to provide plants with optimal conditions for growth. There are many components that go into creating these structures so that plants can properly grow within them. Greenhouses have been around for a very long time but modern technology has allowed us to develop larger and more advanced greenhouses.

5 Works Cited Title Page Imagine Flickr. August 7, March 27, < Figure 1. (labels added) Greenhouse Structure. Drawing. Greenhouse Farming March 27, < Figure 2 & 3 Greenhouse styles. & Connected Greenhouse. Drawing & Photo. Greenhouse Types and Structures March 27, < ures/greenhouse_types_and_structures_print.html> Figure 3A. (unmodified) Attached Greenhouse. Photo. Windsor Greenhouses March 27, < Figure 3C. (unmodified) Detached greenhouse. Photo. United Greenhouse Systems March 27, <

Greenhouse Structures: More than a high tunnel

Greenhouse Structures: More than a high tunnel Steven E. Ph.D., A.A.F. Extension Greenhouse Crops Specialist and Professor of Floriculture Horticulture and Landscape Architecture Colorado State University