On average, with average gardening skills and productivity, it is possible to produce around 2.5 pounds of fresh food per square foot of a Greenhouse every year. This is supported by the U.S. Department of Agriculture, which cites a figure of 420.1 pounds for U.S. per capita, based on efficient and satisfactory growth results. Depending on the type of produce grown, yields can vary greatly. For example, if you grow tomatoes in your greenhouse, you can expect to yield around 50 pounds for every 100 square feet. Additionally, cucumbers can yield around 60 pounds per 100 square feet, and peppers can yield bushels per 100 square feet. To meet the needs of a family of four, it is recommended to space rows between 4-6 feet apart in order to achieve the best yields.