Greenhouse Structures By Tony Watkins For Horticulture

What are the common greenhouse designs? A greenhouse is a structure enclosed by glass or plastic that allows light transmission for the growth of plants. There are four basic styles of greenhouse design.

Lean-to greenhouse The lean-to greenhouse shares a wall with a building and relies on the building structure to provide some support for the greenhouse roof.

Even-span greenhouse Even-span greenhouse structures are single houses that have roofs with an even pitch and an even width. A common even-span greenhouse that uses arching pipes for the framework is called a hoop house.

Uneven-span greenhouses Uneven-span greenhouses have unequal pitches and widths. Use of this style is limited to hillsides. Modern greenhouses are built on level ground. Therefore uneven span greenhouses are rarely built.

Ridge-and-furrow greenhouse (Gutter Connect) Ridge-and-furrow greenhouse structures consist of a number of greenhouses connected along the length of the house. The shared interior walls reduce energy costs and allow for large interior spaces. Ridge-and-furrow greenhouses are best oriented north and south to reduce permanent shadows on the crops created by the gutters.

What are the parts of a Greenhouse? The greenhouse framework supports the greenhouse covering material. Ideally, the framework should be strong, yet allow the maximum amount of light to reach the plants. It is best if it requires little maintenance. Although costly, aluminum and aluminum/steel combination frameworks are popular because they are long lasting and considered to be low maintenance. Other framework materials include wood, galvanized steel, and angle iron.

What materials are used for greenhouse glazing? The covering of the greenhouse is referred to as the glazing. Considerations in choosing a glazing material include durability, light transmission, cost, and affects on heating costs. Flexible sheets of polyethylene are stretched over the greenhouse framework. It is not very durable, but it is inexpensive.

Structured sheets, including polycarbonate, acrylic, and fiberglass materials have grown in popularity. Sheets made with double walls offer good insulation. Polycarbonate structured sheets are most widely used because they have good light transmission, they resist hail damage, and they are easy to work with. Acrylic structured sheets have high light transmission, but they cost more than polycarbonate sheets, are prone to hail damage, and are less flexible. Fiberglass has dropped in popularity. It discolors after 7 to 10 years, is flammable, and provides poor insulation.

Glass is considered to be the best material for crop production Glass is considered to be the best material for crop production. It has the highest light transmission. The fact that it is very long lasting can make it less costly than other glazing materials in the long run.

What are the functions of the headhouse? Many of the tasks that support the production of greenhouse crops takes place in a structure attached to the greenhouse, known as a headhouse. The headhouse might be used as a storage area, a potting area, an office, and/or a shipping area.

What are the advantages of retractable-roof greenhouses? Retractable-roof greenhouse designs allow the roof to be opened and closed. The grower can open the roof when weather conditions are favorable to plant growth and close the roof when the crops need protection. When open, they provide plants with increased light levels and fresh air. Retractable-roof greenhouses can be used to prepare outdoor crops for the elements before leaving the greenhouse. Other advantages include reduced disease problems because of better ventilation, reduced irrigation due to rainfall, and more effective temperature control.

Retractable roof greenhouses

Greenhouse bench options The greenhouse bench is the structure that holds the plants above the ground. Materials used for benches include expanded galvanized steel, aluminum, plastic, and rot resistant wood.

A new type of bench system is called the “ebb and flow” bench which allows water to enter the bottom of the plant by flooding the table. (Right) Benches are arranged in the greenhouse with aisle space and growing space in mind.

Bench Layouts Common layouts include conventional arrangements, peninsular arrangements, and movable benches.

Movable Bench Systems

Controlling Greenhouse Temperature The ability to heat greenhouses is important on cold, cloudy days and at night. Solar energy on sunny days is often enough to keep a greenhouse warm, even in cold weather. There are several different methods used to heat greenhouses. Most plants desire a growing temperature of 55-75° F

Types of Greenhouse Heating Hot water heating systems are the trend in modern greenhouses. A hot water heat system involves heating water in a boiler and pumping the hot water through pipes located in the greenhouse. The pipes are often placed under the benches. These systems have low maintenance and deliver even heat.

Steam heat involves boilers that bring water to a boil and the resulting steam flows through pipes in the greenhouse. Steam heat is not as even as hot water heat.

Small greenhouses are often heated by unit heaters Small greenhouses are often heated by unit heaters. Unit heaters heat air within the unit, then blow the air throughout the greenhouse. Polyethylene tubes attached to the unit help to evenly distribute the airflow. Unit heaters are inexpensive, but cost more to operate than other systems. Unit heaters are commonly used as backup systems.

Greenhouse lighting Greenhouses during particular times of the year must be lit. The most desirable light for greenhouses are high output low energy lights. Examples include: Incandescent, Florescent, High Pressures Sodium Metal Halide

Greenhouse shading Greenhouses, according to crops, must be shaded. Shade cloths come in varies in percentages of shading from 33% to 80%. Modern greenhouses may use retractable shade cloths to control heat and light.

Greenhouse cooling The most common way to cool a greenhouse is with ventilation fans. Fans are used to circulate the air through and inside the house

In addition to ventilation is evaporative cooling In addition to ventilation is evaporative cooling. Cooling pads (cool cell) made of a paper-like material is continually soaked with circulating water. As the fans draw the air through the cell the water cools the air temp as much as 10-20 degrees

Gas environment As energy cost go up greenhouses become tighter and more insulated. Inside air is circulated with heat exchangers which remove the heat from the air and warm fresh air A new and important addition to insulated houses is a CO2 generators, which enrich the inside air with carbon dioxide.