This publication is one of three in a series that covers the basics of developing a nutritional program for producing container-grown plants in greenhouses. A complete nutrition program encompasses the fertilizers, media and water used. The first publication, Plant Nutrition and Fertilizers for Greenhouse Production (PB 1616), develops background information about plant nutrition and discusses the important characteristics of fertilizers used in greenhouse production. This publication examines the effect of water quality on a greenhouse nutritional program. The third publication, Growing Media for Greenhouse Production (PB 1618), describes the important physical and chemical properties of growing media, media testing procedures and interpretation of test results. The objective of this series of publications is to provide basic information that will allow greenhouse operators to develop a nutritional program for their specific business