As the nights grow colder, the harsh winter temperature is a critical factor in not only how we feel, but our plants as well. A hard freeze is more than just a cold night, it’s a stretch of temperatures cold enough, and long enough, to cause real damage.

In meteorology, a hard freeze typically means temperatures falling to 28 degrees Fahrenheit or colder, lasting for usually at least 1 to 3 hours. That duration matters, because it allows the cold to penetrate deeper into soil, plants, and infrastructure rather than just nipping the surface.

Hard freezes are especially impactful because they can kill or severely damage vegetation, including crops and landscaping that might otherwise survive a brief frost. Once temperatures dip below that 28 degree threshold, the water inside plant cells can freeze and expand, rupturing the cell walls. That’s why a hard freeze often marks the true end of a growing season, even in places accustomed to chilly nights.

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Beyond plants, hard freezes can affect people and communities. Exposed pipes are more likely to burst, road surfaces can develop new cracks, and untreated bridges can turn slick. They also stress energy systems as heating demand spikes. This is why meteorologists carefully track hard freezes and cold weather warnings are issued if needed.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.