Frost, Freeze, Hard Freeze

What is the real difference between a frost and a freeze?  When water vapor condenses and freezes without first becoming dew, a thin layer of ice crystals form – this is frost.  It generally has to be below 36 degrees to frost and include clear skies, moisture present and little wind.  Plant tissue can be impacted, but not as severely as a freeze.

When the surface air temperature falls to 32 degrees or below, you have a freeze.  Generally, if it is above 29 degrees, it is a light freeze that can kill most tender plants.  If it is below 28 degrees, then it is considered a killing freeze or hard freeze – this freeze kills annuals and initiates shutdown of hardy perennials.  After three hard freezes, most winter hardy perennial forages are dormant. Once dormant, they can be grazed with less harm to energy reserves.

There are times or situations when grazing prior to dormancy or a killing freeze is what is needed.  If you want to suppress spring growth, then grazing hard prior to dormancy can be beneficial.  If you are frost-seeding clover into the field later this winter, this suppression of the grasses in the spring provides a longer window for the clover to grow and become established due to reducing the competition of the existing perennial grasses.  I’ve also found fields that have become dominantly grass, especially a monoculture of tall fescue, can be grazed hard prior to early fall pre-dormancy and, if a good seed bank is present, you can have increased diversity – more clover the following year. 

Utilize less freeze tolerant forages first.  Orchardgrass loses value fairly quickly after several heavy frosts and literally falls apart after several hard freezes.  Tall fescues hold their value a long time and are the easiest and most ideal for long term stockpiling so save them for last. ~ Excerpt from Victor Shelton’s Grazing Bites Newsletter. Past issues available at https://www.nrcs.