This book provides a detailed description of cytokinins, and their potential for use as plant growth regulator on ornamental crops. A historical view of plant growth regulator use on commercial ornamental plant production in the United States is provided. Then, a detailed description of cytokinins is given, including the physical properties of cytokinins, their effects on plants, their potential for use as a plant growth regulator on ornamental crops, and the various methods by which cytokinins may be applied to plants. This is followed by reference tables that summarize most of the research done with cytokinins on horticultural crops since 1955. The tables are divided by crop type; herbaceous ornamental crops, cut flowers, woody ornamental crops, and non-ornamental horticultural crops.