A greenhouse may be used for many purposes throughout a year. You may produce vegetable crops, grow vegetable transplants for vegetable producers, produce ornamentals, and flower production. Many greenhouse operators have very little time when a crop is not being produced. This helps with their cash flow as they can sell almost year-around. According to the United States Department of Agriculture's (USDA) National Agricultural Statistics Service (NASS), in 2012 Pennsylvania's greenhouses generated $9.5M in sales of crops excluding tomatoes.
Greenhouses may be constructed at least two ways. Some greenhouses are covered with hard plastic panels and tend to withstand snow loads during winter storms. Others are covered with a double layer of plastic with an air space between the two layers. This method may be cheaper to install but the plastic may need to be replaced after three to five years. Some high tunnels have both ends covered with both heat and ventilation installed but normally have only one layer of plastic covering.
Because the greenhouse is a totally enclosed structure, you control the application of water, temperature, and the ventilation. There are several methods of greenhouse production but many greenhouses produce crops traditionally produced in the soil by building wooden benches where the crops are produced. This makes production somewhat easier because the crops are off the ground and bending over is not required.
You will need access to an adequate supply of water to make sure the crops are growing well. Most greenhouses use trickle irrigation so fertigation, which many crops will require, is possible. Trickle irrigation also conserves water and reduces disease pressure because there is no wetting of the crops which reduces fungal diseases. During extreme temperature spikes, overhead misting may be required to minimize the severe temperatures.
Pesticide applications require additional safety precautions because you are working in a closed environment. Respirators or self-contained breathing apparatuses are required for many pesticides used. Read all pesticide labels as greenhouse applications are not the same as pesticides applied to the same crops being produced in the field. This is especially true for Re-entry Intervals (REI) included on the pesticide label.
You will need a heat source for winter production. During the late spring to early fall, the sun usually produces enough heat for most crop production however; this is not true for colder months. The heat will also allow for off-season crop production when prices for local vegetables or other crops should command higher prices. You will need the higher prices to offset the increase in production costs.
During the months when heat is not required, the ventilation system will help maintain a more constant temperature so crops are not damaged by high temperatures. Most ventilation systems are electronically controlled so constant monitoring is not required.
Because greenhouses rely on heat and ventilation, an uninterrupted supply of electricity is critical. You may wish to include a back-up generator in your planning process. The additional cost will probably be offset by not having a major crop loss during a winter snow storm or summer thunder storm.
Before erecting a greenhouse, conduct your market research to determine what crops you may wish to produce. Greenhouse production will require more management than producing the same crops in the field. They may provide a more consistent income from a small space so consider what crops you may wish to produce during the off-seasons.
There are companies that sell and construct greenhouses that can be easily found on the Internet. You should conduct your research into these companies to determine which best suit your needs.