Cool temperatures encourage tillering and more extensive root development prior to entering the reproductive stage. Large head size and higher yield potential is also encouraged by cool temperatures during early development. Frost damage to small grains is highly dependant on the stage of the crop, the temperature and duration of the low temperature, and environmental conditions that existed before the frost occurred. Small grains are among the most frost tolerant of crops. When temperatures fall below 50 o F for several days before a frost, the crop goes through a hardening process and develops more tolerance.
Drought stress can also cause hardening.
Up to jointing small grains can easily withstand temperatures of 25 o F. After jointing the growing point moves above the soil surface and is more susceptible to frost damage. Small grains are most susceptible to frost from the late boot through flowering. F. This is the stage when reproductive tissue development is occurring. Anthers, the pollen producing structures are easily damaged preventing or severely reducing pollen production. Barley is more susceptible to frost injury during the boot stage because it flowers while still in the boot.