Sometimes
plants do die in such cold weather as we are having in Arkansas this
week. Most die when people push their luck and try to grow something
that isn't hardy in their area, or when winter becomes extraordinarily
cold for an extended period or shows up too early. But under normal
circumstances, plants don't just sit there wishing they could go
inside-they acclimate in stages.
As
summer days grow shorter, plants begin "freezing acclimation" by
producing
hormones that slow growth and induce dormancy. By the first hard frost,
they are ready for freezing temperatures, and for beginning the second
stage of their preparation.
The
year's first below-freezing temperatures freeze the water found between
plant cells. Since there is now more liquid water inside the cell than
outside, osmotic pressure draws some of the water out of the cell,
where falling temperatures cause it to freeze as well. Inside the
cells, the concentration of cell parts increases as more water is drawn
out. The more concentrated
the cell parts, the lower the freezing point. So down to a particular
temperature, different for each species, the cells themselves won't
freeze, and the plant will survive. Below that temperature, the plant
will suffer die back, starting in its branch tips because they are
thinner and more exposed to the cold. But branches are expendable.
The soil and any snow cover insulate the roots somewhat; if the roots
survive, so will the plant.
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