One of the cheapest greenhouses are plastic greenhouses. They can be constructed in minutes or hours instead of days, and can easily be dismantled in an even shorter amount of time. They make excellent temporary greenhouses that can be set up in early spring to allow sprouts to get started and then dismantled after the threat of frost has passed to allow the plants to grow in the sun.
Plastic greenhouses are most often constructed of PVC pipes and fittings and then wrapped in a thick, clear plastic sheet, often polyurethane. Some plastic is clear allowing good light transmission, but it will often yellow over time. Other plastic coverings are white which provides uniform light transmission, making sure no plant gets scorched from excessive sun.
Plastic greenhouses do not last nearly as long as a glass greenhouse, but they are only a fraction of the cost. The materials will need to be replaced every couple of years, so if a long term greenhouse is envisioned a plastic greenhouse may not be the best idea, but they both work in the same way.
