Growing season length
Most grape varieties need a growing season of at least 165 days defined by the number of days between the date of the last freezing temperatures (0 Celsius or 32 Fahrenheit, or lower) in the spring and the first freezing temperatures in the following fall season. (Note: August 1st is arbitrarily set as the first day of the fall season.) This map illustrates patterns in growing season length across the state, with maximum values in the southwestern and southeastern corners of the Lower Peninsula and minimum values in interior areas of the northern Lower Peninsula and western Upper Peninsula . Specific sites in the region will have longer or shorter growing seasons based on micro- and mesoclimate. (See Extension Bulletin, Vineyard Establishment I E-2644 - view text, ordering information)