There are hundreds of varieties of wheat produced in the United States, all of which fall into one of six recognized classes: Hard Red Winter, Hard Red Spring, Hard White, Soft White, Durum, and Soft Red Winter. California grows all of the U.S. wheat classes except Soft Red Winter.
Wheat has two distinct growing seasons. Winter wheat is sown in the fall or winter and harvested in the spring or summer; spring wheat is planted in the spring and harvested in late summer or early fall. Most varieties grown in California are genetically spring wheat varieties, i.e. do not require vernalization, however because the majority of California wheat-growing regions have very mild winter temperatures, spring wheat can be sown in the fall or early winter. Since market classifications typically refer to the season of production, not growth habit, California's red wheat production is referred to as Hard Red Winter wheat.
Wheat classes are determined not only by the time of year they are planted and harvested, but also by their hardness, color and the shape of their kernels. Each class of wheat has similar family characteristics, especially as related to milling and baking or other food use.