<u’ve been out in the Arb prairies at all during the past few weeks, you might have noticed that the lush grass and flowers of September are now gradually rusting away into an autumnal copper. Familiar prairie plants such as Virginia Mountain Mint and Blazing Star are already beginning to look ghostly. In the past few weeks, we have also had our first freeze, so our prairies are responding to the falling temperatures.
Late and early freezes in particular can be damaging to plants, especially crops and garden plants less fit to weather the Minnesota climate. The main hazard of frost to plants is not the cold temperatures themselves, but rather the state change of water. Frost damage can occur in plants as a result of ice forming inside the cell, which can harm the cell membrane and result in cell death. An adaptation that some plants have developed in response to this is extracellular freezing. As temperatures drop, plant cells simply release water so that it freezes in the plant tissue rather than the interior of the cell. But because of water loss, this extracellular freezing can still lead to such hazards as cell dehydration and anoxia if plants are unprotected from the cold.
In Minnesota, where temperatures fall well below freezing every winter, many prairie plants are not dying, but simply going into a state of dormancy. These plants withdraw water and metabolic activity from their above-ground stems, leaves, and flowers, and living tissue retreats to the roots. Typically only the topmost layers of soil freeze during the Minnesota winter, so deep roots can continue to grow and assimilate nutrients throughout the winter.
Now that you know a little bit about the bullets they’re dodging, take a moment to appreciate the Minnesota prairie’s preparations for winter. Such seasonal adaptations may be less obvious than squirrels gathering walnuts or roves of warblers on their way south, but they are surely just as worthy of our admiration.