How Much Light Do I Need in a Small Greenhouse?

Natural Sunlight Requirements

• Whether growing vegetables, exotic tropicals or herbs, plants thrive with proper amounts of sunlight. According to the Iowa State University Extension service, most vegetables require at least six hours of full sun per day to produce a healthy crop. Cool-weather crops like lettuce, spinach and cabbage tolerate partial shade. Orchids and houseplants grow well under greenhouse conditions particularly because humidity levels can be controlled. Their light requirements vary according to the varieties selected. If natural sunlight cannot be optimized, artificial lighting can be utilized to supplement it.

Greenhouse Location

• Observe the movement of the sun and the shade lines it creates over several seasons. Locate the greenhouse where it is exposed to maximum sunlight in all seasons. Choose a location on the south side of a building or line of trees. Second-best is the southeastern side. Utilize deciduous shade trees, such as maple or fruit, if afternoon sun becomes too intense. These allow full light to penetrate during the dark winter months when the sun is at its lowest level. Long, morning sunshine is ideal for maximum plant synthesis.

Coverings

• Choosing the material used to cover the greenhouse requires evaluation of optimum light penetration, strength against weather conditions and budget considerations. Glass, film-plastic and high quality fiberglass coverings have a 90 percent light transmission. Double-layer resin sheets of rigid polycarbonate or acrylic transmit approximately 80 percent of the light. Some plastic materials are treated to block out harmful rays. Others hold heat inside, mimicking glass, and save on heating costs. A product may cost five times as much as another, but may last five times longer. If permanence is not required, choose the least expensive film coverings.