<Tr> <Th> Introduced </Th> <Td> 1970 </Td> </Tr> <P> The Shamrock Shake is a seasonal green mint flavored milkshake dessert sold at select McDonald's during March to celebrate St. Patrick's Day . </P> <P> The Shamrock Shake was first introduced in 1970 . Rogers Merchandising in Chicago created the shake . Initially, the shake was lemon / lime flavored with vanilla ice cream, lemon / lime sherbet, and vanilla syrup . By 1973, the shake was merely a green colored vanilla shake, eliminating the lemon / lime sherbet . It is now mint flavored . </P> <P> Shamrock Shakes are sold at select U.S. and Canadian stores during the months of February and March, as well as in Ireland . </P>

When did mcdonald's start selling shamrock shakes