No type of agriculture can be establish ed profitably in a region unless the risk of loss to that type o f agriculture from unfavorable weather conditions is more than balanced by the profits of other times. The farmer should know the risk involved in raising a given crop at a given time. One of these weather risks is minimum temperatures. Minimum temperatures are important at all times of the year, but at certain times, the occurrence of especially critical temperatures is of extreme importance. A killing freeze is often a factor limiting production. Killing freezes may occur in the spring to damage perennial crops that start growth early in the season, o r annual plants that get an early start and are then injured by a late spring freeze . Killing freezes may also occur in the fall and terminate the growing season. In either case , severe damage can be caused and heavy losses incurred . Injury may also occur to perennial crop s from sub zero winter temperatures, but that type of freezing weather will not be covered in this report.