If you have a greenhouse and are interested in growing your own food, a method that is definitely worth looking into is hydroponics. Hydroponics is a method of growing plants (a very wide variety of them) through the use of mineral solutions and water, i.e no soil. This may sound pretty drastic and maybe even unnatural, but there are clear benefits to a well managed hydroponics garden.
Hydroponics systems generally allow for a more precise management system than a soil based growing method. This is because you can decide precisely how much nutrients they get and also the temperature of the roots can be easily maintained. They tend to grow more quickly as a result.
Typically hydroponics are used to grow certain fruit a vegetables which adapt well to the unique environment, including things like lettuce, spinach, melon and more. You can also grow a number of plants purely for their aesthetics.