How Low Can Plants Go?

Arctic air is here, and we’re in the throes of a winter cold blast. Below zero stings the skin and I find myself hurrying a bit more quickly outdoors. Wind-chill makes me hustle even faster.

Luckily plants don’t feel wind-chill. Most of the trees, shrubs and perennials in our landscapes are hardy lots; the non-adapted get weeded out as winter separates the wheat from the chaff.

But even our well-adapted plants have their limits. How low can they go?

North Dakota and Minnesota are located in USDA Hardiness Zones 3 and 4, and most gardeners respectfully shop for plants suited to their zone. These zone numbers are easy to remember; less easily remembered are the temperature extremes they’re based upon. 

USDA Hardiness Zones are based on the average minimum winter temperatures that a region receives. If temperatures dip below those points, plants can be injured or killed.

Here are the minimum winter temperatures upon which our zones are based:

  • zone 3a = -40 degrees F.
  • zone 3b = -35 degrees F.
  • zone 4a = -30 degrees F.
  • zone 4b = -25 degrees F.

Whether or not plants survive at these temperatures (or even temps not as cold) depends greatly on the amount of snow that is insulating the ground. If snow is scarce, plants can be injured at less extreme temperatures, as cold penetrates more severely into poorly protected soil.