Instead, water outside the cell freezes, thereby causing water from inside the cell to move to move outside the cell to form more ice, he explained. The water moving out of the cell reduces the amount of freezable water within the cell. Inside plant cells, sugars and other things then become more concentrated, forming natural antifreeze. The development of hardiness in the fall and early winter is a slow, gradual process. The loss of hardiness in late winter and early spring is dependent of temperature.
Plants lose hardiness faster with warmer temperatures.
Once growth begins in the spring, plants lose their ability to acclimate and become susceptible to freezing temperatures. Roots are less hardy than stem or above ground tissues because they are exposed to less cold under the soil, he said. And in general, tissues or organs that are actively growing are least hardy.