The alfalfa (Medicaqo sativa L.) seedling develops into a mature plant by differentiation of several stems which form the primary crown. The initial four stems are the primary stem, two stems differentiating from the axils of the cotyledons and a stem from the axil of the unifoliolate leaf. Establishment of the primary crown is dependent on the development of these initial stems and the degree to which contractile growth occurs. Allof these processes are influenced by soil temperature, and to a lesser extent, by photoperiod. We have determined optimum temperatures for alfalfa seedling development to be in the range of 68 to 72 degrees fahrenheit depending on the dormancy classification of the cultivar. Using this information and climatic information for a given area in California it may be possible to predict the most desirable time to plant alfalfa in that area.