There is no official USDA or Federal definition of a greenhouse tomato. Here, we define greenhouse tomatoes as those grown in fixed structures, as opposed to open fields or temporary structures, such as shade houses. Both shade houses and greenhouses are referred to as protected culture, offering advantages relative to open-field production. A shade house is a temporary structure that supports shade cloth, a type of screen that provides some passive environmental control, such as shading the plants from excessive sunlight and wind. Growers using fixed structures can choose the degree of environmental control to adopt and whether to grow in soil or use hydroponics, a production system where plants are grown in a nutrient solution with an artificial medium to provide mechanical support to the root system. Active environmental control could include heating, cooling, humidity control, and use of carbon dioxide to boost yields. Growers select technologies based on environmental and economic considerations.

All the large commercial greenhouses in the United States and Canada use active climate control and hydroponics, and many U.S. and Canadian growers would like to define a greenhouse tomato as one grown in that type of greenhouse. Although some greenhouse growers in Mexico have similar technology levels, others produce in greenhouses with lower technology systems, perhaps without fully active climate control, hydroponics, or both. Lower technology systems are less costly than high-technology greenhouses, but they produce lower yields and a less consistent product. However, this article uses a broader definition of greenhouses (not requiring active control and hydroponics) in order not to exclude expanding production volumes in Mexico. While this definition excludes shade houses, in reality all of protected culture will impact the North American fresh tomato industry, since shade houses are becoming more common in Mexican export-oriented field production regions, and it is becoming increasingly difficult to distinguish greenhouse and shade house production in the marketplace.