What makes winter wheat a winter wheat?
For most of us wheat is a wheat; however, there is a distinct difference between spring and winter wheat, even though the vegetative characteristics of two wheat types are very similar. Winter wheat can withstand freezing temperatures for extended periods of time during early vegetative stage and requires exposure to freezing or near freezing temperatures (vernalization) to trigger reproductive stage. In other words, if winter wheat doesn’t go through a period of cold temperature, then it wouldn’t produce seed. Two things needed for winter wheat to perform at optimum level and produce good yield are- Cold Acclimation and Vernalization.
New emerged winter wheat seedlings in early fall are no different than spring wheat seedlings. In order to survive through cold winters with subfreezing temperatures, winter wheat has to be exposed to series of cooler temperatures early in the growth stage, which is called ‘cold acclimation’ or simply ‘hardening’. The acclimation is possible due to gradual decrease in daily temperature in the fall after the wheat has been emerged. Winter wheat plants adapt to rapidly decreasing temperatures in late fall or winter by lowering moisture content of the ‘crown’ (the growing point at the base of the shoot), decreasing the accumulation of carbohydrates, and slowing down the overall growth process. This helps in great deal to resist frost and other winter conditions that a winter wheat plant has to go through in its life cycle. Cold acclimation generally starts when the temperature starts falling below 50F.
Once the cold acclimation is achieved, winter wheat requires to go through extended period of below 40F temperatures to trigger reproductive phase the next spring. Amount of time and range of temperature required varies among varieties. Winter wheat varieties that are adapted to northern climate are usually more tolerant to extended subfreezing temperatures than the ones adapted to southern environment. The most winter hardy varieties can withstand crown temperatures as low as -15F.
Better winter survival is achieved when winter wheat is seeded into crop stubble (or no-tilled) and plants are 3-4 tiller stage in the fall when going into winter. Crop stubble helps catch snow throughout the winter and form insulating blanket, increasing chances of winter survival significantly. Snow also plays a major role in providing moisture need the following spring.