How Do Floating Row Covers Protect Plants From Frost?

By on February 21, 2013

Heat radiates from the soil at night & floating row covers hold the heat in.

When it comes to protecting your plants from frosts and freezes it’s important to understand where the heat is coming from.

Soil absorbs heat during the day and radiates it back at night. Our Agribon floating row covers work by trapping the heat that rises from the soil. That’s why you need to drape row cover to the ground, to keep the heat from seeping out.

In our video and article we teach you how to make low tunnels to protect your crops from frosts.

Did you know frosts and freezes are two different things?

A radiation frost happens when the weather is clear and the wind is still. The sun warms the soil during the day and there is no cloud cover to stop the heat in the soil (and the plants, for that matter) from escaping higher into the atmosphere. Row covers work well in frosts.

An advective freeze happens when it is windy and a mass of cold air brings freezing temperatures. When a freeze comes you need more help to keep the soil and plants warm. Tricia demonstrates these extra steps in our video.

Put down a layer of plastic mulch right on the soil.

Plug in traditional (not LED) Christmas tree lights to generate heat.

Get some passive solar heat with water—it’s a great heat reservoir, even better than soil. In addition, there is a latent heat release when water freezes.

If an advective freeze is forecast, fill milk jugs or five gallon buckets with water and place them in the tunnel near your plants.

wall o water
Following the same principle, give your plants extra protection with a “mini-greenhouse” Wall-O-Water around each plant.

Use row covers for typical frosts—but if a freeze is in the offing, take extra precautions.

For more information about frosts and freezes we recommend articles by North Carolina State University and Texas A&M.

  Comments (4)


Posted by on Nov. 01, 2013 at 11:01:15 AM


I would be careful about using water to trap/release heat.  It takes twice as much energy to warm water as it does to cool it.  There is some scientific study that indicates jugs of water placed in low tunnels actually has a cooling effect overall.  You may want to research this.

Posted by norm on Sep. 18, 2014 at 5:25:54 PM


Thanks for posting this!  I’ve been trying to figure out the best ways to protect my plants and it seems to vary by region.

Posted by Jeanie on Nov. 16, 2014 at 10:13:37 PM


Here is the scientific explanation about using jugs of water in tunnels:
Water releases energy (‘heat”) to freeze.
Water needs energy (“heat”) to unfreeze.

In other words, place the jugs in the tunnel for the night and the water will even give off heat as it freezes.
Remove the frozen jugs in the morning as the outside air temperature returns to over 32 degrees F.  Otherwise the ice will absorb heat from the bed under the tunnel until it is water. And the bed, therefore, remains cold during that time.

Posted by Bettina Hughes on Dec. 08, 2016 at 6:02:59 AM

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